Manpages - cmake-policies.7

NAME
INTRODUCTION
POLICIES INTRODUCED BY CMAKE 3.22
- CMP0128
- CMP0127
POLICIES INTRODUCED BY CMAKE 3.21
- CMP0126
- CMP0125
- CMP0124
- CMP0123
- CMP0122
- CMP0121
POLICIES INTRODUCED BY CMAKE 3.20
- CMP0120
- CMP0119
- CMP0118
- CMP0117
- CMP0116
- CMP0115
POLICIES INTRODUCED BY CMAKE 3.19
- CMP0114
- CMP0113
- CMP0112
- CMP0111
- CMP0110
- CMP0109
POLICIES INTRODUCED BY CMAKE 3.18
- CMP0108
- CMP0107
- CMP0106
- CMP0105
- CMP0104
- Examples
- CMP0103
POLICIES INTRODUCED BY CMAKE 3.17
- CMP0102
- CMP0101
- CMP0100
- CMP0099
- CMP0098
POLICIES INTRODUCED BY CMAKE 3.16
- CMP0097
- CMP0096
- CMP0095
POLICIES INTRODUCED BY CMAKE 3.15
- CMP0094
- CMP0093
- CMP0092
- CMP0091
- CMP0090
- CMP0089
POLICIES INTRODUCED BY CMAKE 3.14
- CMP0088
- CMP0087
- CMP0086
- CMP0085
- CMP0084
- CMP0083
- Examples
- CMP0082
POLICIES INTRODUCED BY CMAKE 3.13
- CMP0081
- CMP0080
- CMP0079
- CMP0078
- CMP0077
- CMP0076
POLICIES INTRODUCED BY CMAKE 3.12
- CMP0075
- CMP0074
- CMP0073
POLICIES INTRODUCED BY CMAKE 3.11
- CMP0072
POLICIES INTRODUCED BY CMAKE 3.10
- CMP0071
- CMP0070
POLICIES INTRODUCED BY CMAKE 3.9
- CMP0069
- Examples
- CMP0068
POLICIES INTRODUCED BY CMAKE 3.8
- CMP0067
POLICIES INTRODUCED BY CMAKE 3.7
- CMP0066
POLICIES INTRODUCED BY CMAKE 3.4
- CMP0065
- CMP0064
POLICIES INTRODUCED BY CMAKE 3.3
- CMP0063
- CMP0062
- CMP0061
- CMP0060
- CMP0059
- CMP0058
- CMP0057
POLICIES INTRODUCED BY CMAKE 3.2
- CMP0056
- CMP0055
POLICIES INTRODUCED BY CMAKE 3.1
- CMP0054
- CMP0053
- CMP0052
- CMP0051
POLICIES INTRODUCED BY CMAKE 3.0
- CMP0050
- CMP0049
- CMP0048
- CMP0047
- CMP0046
- CMP0045
- CMP0044
- CMP0043
- CMP0042
- CMP0041
- CMP0040
- CMP0039
- CMP0038
- CMP0037
- CMP0036
- CMP0035
- CMP0034
- CMP0033
- CMP0032
- CMP0031
- CMP0030
- CMP0029
- CMP0028
- CMP0027
- CMP0026
- CMP0025
- CMP0024
POLICIES INTRODUCED BY CMAKE 2.8
- CMP0023
- CMP0022
- CMP0021
- CMP0020
- CMP0019
- CMP0018
- CMP0017
- CMP0016
- CMP0015
- CMP0014
- CMP0013
- CMP0012
POLICIES INTRODUCED BY CMAKE 2.6
- CMP0011
- CMP0010
- CMP0009
- CMP0008
- CMP0007
- CMP0006
- CMP0005
- CMP0004
- CMP0003
- CMP0002
- CMP0001
- CMP0000
COPYRIGHT

NAME

cmake-policies - CMake Policies Reference

INTRODUCTION

Policies in CMake are used to preserve backward compatible behavior across multiple releases. When a new policy is introduced, newer CMake versions will begin to warn about the backward compatible behavior. It is possible to disable the warning by explicitly requesting the OLD, or backward compatible behavior using the cmake_policy() command. It is also possible to request NEW, or non-backward compatible behavior for a policy, also avoiding the warning. Each policy can also be set to either NEW or OLD behavior explicitly on the command line with the CMAKE_POLICY_DEFAULT_CMP<NNNN> variable.

A policy is a deprecation mechanism and not a reliable feature toggle. A policy should almost never be set to OLD, except to silence warnings in an otherwise frozen or stable codebase, or temporarily as part of a larger migration path. The OLD behavior of each policy is undesirable and will be replaced with an error condition in a future release.

The cmake_minimum_required() command does more than report an error if a too-old version of CMake is used to build a project. It also sets all policies introduced in that CMake version or earlier to NEW behavior. To manage policies without increasing the minimum required CMake version, the if(POLICY) command may be used:

#+begin_quote

      if(POLICY CMP0990)
        cmake_policy(SET CMP0990 NEW)
      endif()

#+end_quote

This has the effect of using the NEW behavior with newer CMake releases which users may be using and not issuing a compatibility warning.

The setting of a policy is confined in some cases to not propagate to the parent scope. For example, if the files read by the include() command or the find_package() command contain a use of cmake_policy(), that policy setting will not affect the caller by default. Both commands accept an optional NO_POLICY_SCOPE keyword to control this behavior.

The CMAKE_MINIMUM_REQUIRED_VERSION variable may also be used to determine whether to report an error on use of deprecated macros or functions.

POLICIES INTRODUCED BY CMAKE 3.22

CMP0128

New in version 3.22.

When this policy is set to NEW:

The OLD behavior:

Code may need to be updated for the NEW behavior in the following cases:

If extensions were disabled without <LANG>_STANDARD being set CMake previously wouldn’t actually disable extensions.

Such code should be updated to not disable extensions if they are required.

If extensions were enabled/disabled when <LANG>_STANDARD was satisfied by the compiler’s default CMake previously wouldn’t actually enable/disable extensions.

Such code should be updated to set the correct extensions mode. #+end_quote

If compiler flags affecting the standard mode are used during compiler detection (for example in a toolchain file using CMAKE_<LANG>_FLAGS_INIT) then they will affect the detected default standard and extensions.

Unlike many policies, CMake version 3.22.1 does not warn when the policy is not set and simply uses the OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly. See documentation of the CMAKE_POLICY_WARNING_CMP0128 variable to control the warning.

NOTE:

#+end_quote

CMP0127

New in version 3.22.

cmake_dependent_option() supports full Condition Syntax.

The <depends> parameter accepts a semicolon-separated list of conditions. CMake 3.21 and lower evaluates each condition as if(${condition}), which does not properly handle conditions with nested paren groups. CMake 3.22 and above instead prefer to evaluate each condition as if(<condition>), where <condition> is re-parsed as if literally written in a call to if(). This allows expressions like:

#+begin_quote

      "A AND (B OR C)"

#+end_quote

but requires expressions like:

#+begin_quote

      "FOO MATCHES (UPPER|lower)"

#+end_quote

to be re-written as:

#+begin_quote

      "FOO MATCHES \"(UPPER|lower)\""

#+end_quote

Policy CMP0127 provides compatibility for projects that have not been updated to expect the new behavior.

This policy was introduced in CMake version 3.22. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.21

CMP0126

New in version 3.21.

When this policy is set to NEW, the set(CACHE) command does not remove any normal variable of the same name from the current scope. The OLD behavior removes any normal variable of the same name from the current scope in the following situations:

Note that the NEW behavior has an important difference to the similar NEW behavior of policy CMP0077. The set(CACHE) command always sets the cache variable if it did not exist previously, regardless of the CMP0126 policy setting. The option() command will not set the cache variable if a non-cache variable of the same name already exists and CMP0077 is set to NEW.

Policy CMP0126 was introduced in CMake version 3.21. Use the cmake_policy() command to set it to OLD or NEW explicitly within a project. Use the CMAKE_POLICY_DEFAULT_CMP0126 variable to set the policy for a third-party project in a subdirectory without modifying it. Unlike many policies, CMake version 3.22.1 does not warn when the policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0126 variable to control the warning.

NOTE:

#+end_quote

CMP0125

New in version 3.21.

The find_file(), find_path(), find_library() and find_program() commands cache their result in the variable specified by their first argument. Prior to CMake 3.21, if a cache variable of that name already existed before the call but the cache variable had no type, any non-cache variable of the same name would be discarded and the cache variable was always used (see also CMP0126 for a different but similar behavior). This contradicts the convention that a non-cache variable should take precedence over a cache variable of the same name. Such a situation can arise if a user sets a cache variable on the command line without specifying a type, such as cmake -DMYVAR=blah … instead of cmake -DMYVAR:FILEPATH=blah.

Related to the above, if a cache variable of the specified name already exists and it does have a type, the various find_…() commands would return that value unchanged. In particular, if it contained a relative path, it would not be converted to an absolute path in this situation.

When policy CMP0125 is set to OLD or is unset, the behavior is as described above. When it is set to NEW, the behavior is as follows:

This policy was introduced in CMake version 3.21. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike many policies, CMake version 3.22.1 does not warn when the policy is not set and simply uses OLD behavior.

NOTE:

#+end_quote

CMP0124

New in version 3.21.

When this policy is set to NEW, the scope of loop variables defined by the foreach() command is restricted to the loop only. They will be unset at the end of the loop.

The OLD behavior for this policy still clears the loop variables at the end of the loop, but does not unset them. This leaves them as defined, but empty.

NOTE:

#+end_quote

CMP0123

New in version 3.21.

ARMClang cpu/arch compile and link flags must be set explicitly.

CMake 3.20 and lower automatically maps the CMAKE_SYSTEM_PROCESSOR variable and an undocumented CMAKE_SYSTEM_ARCH to compile and link options for ARMClang. For example, the -mcpu=cortex-m33 flag is added when CMAKE_SYSTEM_PROCESSOR equals cortex-m33. CMake requires projects to set either variable or it raises a fatal error. However, the project may need to additionally specify CPU features using e.g. -mcpu=cortex-m33+nodsp, conflicting with the -mcpu=cortex-m33 added by CMake. This results in either link errors or unusable binaries.

CMake 3.21 and above prefer instead to not add any cpu/arch compile and link flags automatically. Instead, projects must specify them explicitly. This policy provides compatibility for projects that have not been updated.

The OLD behavior of this policy requires projects that use ARMClang to set either CMAKE_SYSTEM_PROCESSOR or CMAKE_SYSTEM_ARCH and it automatically adds a compile option -mcpu= or -march= and a link option –cpu= based on those variables. The NEW behavior does not add compile or link options, and projects are responsible for setting correct options.

This policy was introduced in CMake version 3.21. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0122

New in version 3.21.

UseSWIG use library name conventions for CSharp language.

Starting with CMake 3.21, UseSWIG generates now a library using default naming conventions. This policy provides compatibility with projects that expect the legacy behavior.

NOTE:

#+end_quote

CMP0121

New in version 3.21.

The list() command now detects invalid indices.

Prior to CMake version 3.21, the list() command’s GET, INSERT, SUBLIST, and REMOVE_AT subcommands did not detect invalid index arguments.

The OLD behavior of this policy is for invalid indices to be treated as their integer value (if any) at the start of the string. For example, 2good4you is a 2 and not_an_integer is a 0. The NEW behavior is for invalid indices to trigger an error.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.20

CMP0120

New in version 3.20.

The WriteCompilerDetectionHeader module is removed.

CMake versions 3.1 through 3.19 provide this module to generate a C++ compatibility layer by re-using information from CMake’s table of preprocessor checks for cmake-compile-features(7). However:

For reasons including the above, CMake 3.20 and above prefer to not provide the WriteCompilerDetectionHeader module. This policy provides compatibility for projects that have not been ported away from it. Projects using the module should be updated to stop using it. Alternatives include:

The OLD behavior of this policy is for inclusion of the deprecated WriteCompilerDetectionHeader module to work. The NEW behavior is for inclusion of the module to fail as if it does not exist.

This policy was introduced in CMake version 3.20. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0119

New in version 3.20.

LANGUAGE source file property explicitly compiles as specified language.

The LANGUAGE source file property is documented to mean that the source file is written in the specified language. In CMake 3.19 and below, setting this property causes CMake to compile the source file using the compiler for the specified language. However, it only passes an explicit flag to tell the compiler to treat the source as the specified language for MSVC-like, XL, and Embarcadero compilers for the CXX language. CMake 3.20 and above prefer to also explicitly tell the compiler to use the specified language using a flag such as -x c on all compilers for which such flags are known.

This policy provides compatibility for projects that have not been updated to expect this behavior. For example, some projects were setting the LANGUAGE property to C on assembly-language .S source files in order to compile them using the C compiler. Such projects should be updated to use enable_language(ASM), for which CMake will often choose the C compiler as the assembler on relevant platforms anyway.

The OLD behavior for this policy is to interpret the LANGUAGE <LANG> property using its undocumented meaning to “use the <LANG> compiler”. The NEW behavior for this policy is to interpret the LANGUAGE <LANG> property using its documented meaning to “compile as a <LANG> source”.

NOTE:

#+end_quote

CMP0118

New in version 3.20.

The GENERATED source file property is now visible in all directories.

Whether or not a source file is generated is an all-or-nothing global property of the source. Consequently, the associated GENERATED property is now visible from any directory scope, not only from the scope for which it was set.

Additionally, the GENERATED property may now be set only to boolean values, and may not be turned off once turned on.

The OLD behavior of this policy is to only allow GENERATED to be visible from the directory scope for which it was set. The NEW behavior on the other hand allows it to be visible from any scope.

This policy was introduced in CMake version 3.20. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike many policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses OLD behavior with regard to visibility of the GENERATED property. However, CMake does warn about setting the GENERATED property to a non-boolean value.

CMP0117

New in version 3.20.

MSVC RTTI flag /GR is not added to CMAKE_CXX_FLAGS by default.

When using MSVC-like compilers in CMake 3.19 and below, the RTTI flag /GR is added to CMAKE_CXX_FLAGS by default. This behavior is left from support for MSVC versions from Visual Studio 2003 and below that did not enable RTTI by default. It is no longer necessary. Furthermore, it is problematic for projects that want to change to /GR- programmatically. In particular, it requires string editing of the CMAKE_CXX_FLAGS variable with knowledge of the CMake builtin default so it can be replaced.

CMake 3.20 and above prefer to leave out /GR from the value of CMAKE_CXX_FLAGS by default.

This policy provides compatibility with projects that have not been updated to expect the lack of the /GR flag. The policy setting takes effect as of the first project() or enable_language() command that initializes CMAKE_CXX_FLAGS.

NOTE:

#+end_quote

The OLD behavior for this policy is to place the MSVC /GR flag in the default CMAKE_CXX_FLAGS cache entry. The NEW behavior for this policy is to not place the MSVC /GR flag in the default cache entry.

NOTE:

#+end_quote

CMP0116

New in version 3.20.

Ninja generators transform DEPFILE s from add_custom_command().

In CMake 3.19 and below, files given to the DEPFILE argument of add_custom_command() were passed directly to Ninja’s depfile variable without any path resolution. This meant that if add_custom_command() was called from a subdirectory (created by add_subdirectory()), the DEPFILE argument would have to be either an absolute path or a path relative to CMAKE_BINARY_DIR, rather than CMAKE_CURRENT_BINARY_DIR. In addition, no transformation was done on the file listed in DEPFILE, which meant that the paths within the DEPFILE had the same restrictions.

Starting with CMake 3.20, the DEPFILE argument is relative to CMAKE_CURRENT_BINARY_DIR (unless it is absolute), and the paths in the DEPFILE are also relative to CMAKE_CURRENT_BINARY_DIR. CMake automatically transforms the paths in the DEPFILE (unless they are absolute) after the custom command is run. The file listed in DEPFILE is not modified in any way. Instead, CMake writes the transformation to its own internal file, and passes this internal file to Ninja’s depfile variable. This transformation happens regardless of whether or not DEPFILE is relative, and regardless of whether or not add_custom_command() is called from a subdirectory.

The OLD behavior for this policy is to pass the DEPFILE to Ninja unaltered. The NEW behavior for this policy is to transform the DEPFILE after running the custom command. The status of CMP0116 is recorded at the time of the custom command’s creation, and you can have custom commands in the same directory with different values for CMP0116 by setting the policy before each custom command.

This policy was introduced in CMake version 3.20. Unlike most policies, CMake version 3.22.1 does not warn by default when this policy is not set (unless DEPFILE is used in a subdirectory) and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0116 variable to control the warning.

CMP0115

New in version 3.20.

Source file extensions must be explicit.

In CMake 3.19 and below, if a source file could not be found by the name specified, it would append a list of known extensions to the name to see if the file with the extension could be found. For example, this would allow the user to run:

#+begin_quote

      add_executable(exe main)

#+end_quote

and put main.c in the executable without specifying the extension.

Starting in CMake 3.20, CMake prefers all source files to have their extensions explicitly listed:

#+begin_quote

      add_executable(exe main.c)

#+end_quote

The OLD behavior for this policy is to implicitly append known extensions to source files if they can’t be found. The NEW behavior of this policy is to not append known extensions and require them to be explicit.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.19

CMP0114

New in version 3.19.

ExternalProject step targets fully adopt their steps.

The ExternalProject_Add() STEP_TARGETS option, and the ExternalProject_Add_StepTargets() function, can be used to create build targets for individual steps of an external project.

In CMake 3.18 and below, step targets have some limitations:

In CMake 3.19 and above, the ExternalProject module prefers a revised design to address these problems:

Policy CMP0114 provides compatibility for projects that have not been updated to expect the new behavior. The OLD behavior for this policy is to use the above-documented behavior from 3.18 and below. The NEW behavior for this policy is to use the above-documented behavior preferred by 3.19 and above.

This policy was introduced in CMake version 3.19. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

CMP0113

New in version 3.19.

Makefile Generators do not repeat custom commands from target dependencies.

Consider a chain of custom commands split across two dependent targets:

#+begin_quote

      add_custom_command(OUTPUT output-not-created
        COMMAND ... DEPENDS ...)
      set_property(SOURCE output-not-created PROPERTY SYMBOLIC 1)
      add_custom_command(OUTPUT output-created
        COMMAND ... DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/output-not-created)
      add_custom_target(first DEPENDS output-not-created)
      add_custom_target(second DEPENDS output-created)
      add_dependencies(second first)

#+end_quote

In CMake 3.18 and lower, the Makefile generators put a copy of both custom commands in the Makefile for target second even though its dependency on target first ensures that the first custom command runs before the second. Running make second would cause the first custom command to run once in the first target and then again in the second target.

CMake 3.19 and above prefer to not duplicate custom commands in a target that are already generated in other targets on which the target depends (directly or indirectly). This policy provides compatibility for projects that have not been updated to expect the new behavior. In particular, projects that relied on the duplicate execution or that did not properly set the SYMBOLIC source file property may be affected.

The OLD behavior for this policy is to duplicate custom commands in dependent targets. The NEW behavior of this policy is to not duplicate custom commands in dependent targets.

This policy was introduced in CMake version 3.19. Unlike many policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses OLD behavior.

NOTE:

#+end_quote

CMP0112

New in version 3.19.

Target file component generator expressions do not add target dependencies.

The following target-based generator expressions that query for directory or file name components no longer add a dependency on the evaluated target.

#+end_quote #+end_quote

In CMake 3.18 and lower a dependency on the evaluated target of the above generator expressions would always be added. CMake 3.19 and above prefer to not add this dependency. This policy provides compatibility for projects that have not been updated to expect the new behavior.

The OLD behavior for this policy is to add a dependency on the evaluated target for the above generator expressions. The NEW behavior of this policy is to not add a dependency on the evaluated target for the above generator expressions.

This policy was introduced in CMake version 3.19. Unlike many policies, CMake version 3.22.1 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0112 variable to control the warning.

NOTE:

#+end_quote

CMP0111

New in version 3.19.

An imported target missing its location property fails during generation.

Imported Targets for library files and executables require that their location on disk is specified in a target property such as IMPORTED_LOCATION, IMPORTED_IMPLIB, or a per-configuration equivalent. If a needed location property is not set, CMake 3.18 and below generate the string <TARGET_NAME>-NOTFOUND in its place, which results in failures of the corresponding rules at build time. CMake 3.19 and above prefer instead to raise an error during generation. This policy provides compatibility for projects that have not been updated to expect the new behavior.

The OLD behavior of this policy is to generate the location of an imported unknown, static or shared library target as <TARGET_NAME>-NOTFOUND if not set. The NEW behavior is to raise an error.

NOTE:

#+end_quote

CMP0110

New in version 3.19.

add_test() supports arbitrary characters in test names.

add_test() can now (officially) create tests with whitespace and other special characters in its name. Before CMake version 3.19 that was not allowed, however, it was possible to work around this limitation by explicitly putting escaped quotes around the test’s name in the add_test command.

Although never officially supported several projects in the wild found and implemented this workaround. However, the new change which officially allows the add_test command to support whitespace and other special characters in test names now breaks that workaround. In order for these projects to work smoothly with newer CMake versions, this policy was introduced.

The OLD behavior of this policy is to still prevent add_test from handling whitespace and special characters properly (if not using the mentioned workaround). The NEW behavior on the other hand allows names with whitespace and special characters for tests created by add_test.

CMP0109

New in version 3.19.

find_program() requires permission to execute but not to read.

In CMake 3.18 and below, the find_program() command on UNIX would find files that are readable without requiring execute permission, and would not find files that are executable without read permission. In CMake 3.19 and above, find_program now prefers to require execute permission but not read permission. This policy provides compatibility with projects that have not been updated to expect the new behavior.

The OLD behavior for this policy is for find_program to require read permission but not execute permission. The NEW behavior for this policy is for find_program to require execute permission but not read permission.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.18

CMP0108

New in version 3.18.

A target is not allowed to link to itself even through an ALIAS target.

In CMake 3.17 and below, a target can link to a target aliased to itself.

The OLD behavior for this policy is to allow a target to link to a target aliased to itself.

The NEW behavior of this policy is to prevent a target to link to itself through an ALIAS target.

This policy was introduced in CMake version 3.17. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike many policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses OLD behavior.

NOTE:

#+end_quote

CMP0107

New in version 3.18.

It is not allowed to create an ALIAS target with the same name as an another target.

In CMake 3.17 and below, an ALIAS target can overwrite silently an existing target with the same name.

The OLD behavior for this policy is to allow target overwrite.

The NEW behavior of this policy is to prevent target overwriting.

NOTE:

#+end_quote

CMP0106

New in version 3.18.

The Documentation module is removed.

The Documentation was added as a support mechanism for the VTK project and was tuned for that project. Instead of CMake providing this module with (now old) VTK patterns for cache variables and required packages, the module is now deprecated by CMake itself.

The OLD behavior of this policy is for Documentation to add cache variables and find VTK documentation dependent packages. The NEW behavior is to act as an empty module.

This policy was introduced in CMake version 3.18. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0105

New in version 3.18.

LINK_OPTIONS and INTERFACE_LINK_OPTIONS target properties are now used for the device link step.

In CMake 3.17 and below, link options are not used by the device link step.

The OLD behavior for this policy is to ignore the link options.

The NEW behavior of this policy is to use the link options during the device link step.

NOTE:

#+end_quote

CMP0104

New in version 3.18.

Initialize CMAKE_CUDA_ARCHITECTURES when CMAKE_CUDA_COMPILER_ID is NVIDIA. Raise an error if CUDA_ARCHITECTURES is empty.

CMAKE_CUDA_ARCHITECTURES introduced in CMake 3.18 is used to initialize CUDA_ARCHITECTURES, which passes correct code generation flags to the CUDA compiler.

Previous to this users had to manually specify the code generation flags. This policy is for backwards compatibility with manually specifying code generation flags.

The OLD behavior for this policy is to not initialize CMAKE_CUDA_ARCHITECTURES when CMAKE_CUDA_COMPILER_ID is NVIDIA. Empty CUDA_ARCHITECTURES is allowed.

The NEW behavior of this policy is to initialize CMAKE_CUDA_ARCHITECTURES when CMAKE_CUDA_COMPILER_ID is NVIDIA and raise an error if CUDA_ARCHITECTURES is empty during generation.

If CUDA_ARCHITECTURES is set to a false value no architectures flags are passed to the compiler. This is intended to support packagers and the rare cases where full control over the passed flags is required.

NOTE:

#+end_quote

Examples

#+begin_quote

      set_target_properties(tgt PROPERTIES CUDA_ARCHITECTURES "35;50;72")

#+end_quote

Generates code for real and virtual architectures 30, 50 and 72.

#+begin_quote

      set_property(TARGET tgt PROPERTY CUDA_ARCHITECTURES 70-real 72-virtual)

#+end_quote

Generates code for real architecture 70 and virtual architecture 72.

#+begin_quote

      set_property(TARGET tgt PROPERTY CUDA_ARCHITECTURES OFF)

#+end_quote

CMake will not pass any architecture flags to the compiler.

CMP0103

New in version 3.18.

Multiple calls to export() command with same FILE without APPEND is no longer allowed.

In CMake 3.17 and below, multiple calls to export() command with the same FILE without APPEND are accepted silently but only the last occurrence is taken into account during the generation.

The NEW behavior of this policy is to raise an error on second call to export() command with same FILE without APPEND.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.17

CMP0102

New in version 3.17.

The mark_as_advanced() command no longer creates a cache entry if one does not already exist.

In CMake 3.16 and below, if a variable was not defined at all or just defined locally, the mark_as_advanced() command would create a new cache entry with an UNINITIALIZED type and no value. When a find_path() (or other similar find_ command) would next run, it would find this undefined cache entry and set it up with an empty string value. This process would end up deleting the local variable in the process (due to the way the cache works), effectively clearing any stored find_ results that were only available in the local scope.

The OLD behavior for this policy is to create the empty cache definition. The NEW behavior of this policy is to ignore variables which do not already exist in the cache.

NOTE:

#+end_quote

CMP0101

New in version 3.17.

target_compile_options() now honors BEFORE keyword in all scopes.

In CMake 3.16 and below the target_compile_options() ignores the BEFORE keyword in private scope. CMake 3.17 and later honors BEFORE keyword in all scopes. This policy provides compatibility for projects that have not been updated to expect the new behavior.

The OLD behavior for this policy is to not honor BEFORE keyword in private scope. The NEW behavior of this policy is to honor BEFORE keyword in all scopes.

NOTE:

#+end_quote

CMP0100

New in version 3.17.

Let AUTOMOC and AUTOUIC process header files that end with a .hh extension.

Since version 3.17, CMake processes header files that end with a .hh extension in AUTOMOC and AUTOUIC. In earlier CMake versions, these header files were ignored by AUTOMOC and AUTOUIC.

This policy affects how header files that end with a .hh extension get treated in AUTOMOC and AUTOUIC.

The OLD behavior for this policy is to ignore .hh header files in AUTOMOC and AUTOUIC.

The NEW behavior for this policy is to process .hh header files in AUTOMOC and AUTOUIC just like other header files.

NOTE:

#+end_quote #+end_quote #+end_quote

This policy was introduced in CMake version 3.17.0. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0099

New in version 3.17.

Target link properties INTERFACE_LINK_OPTIONS, INTERFACE_LINK_DIRECTORIES and INTERFACE_LINK_DEPENDS are now transitive over private dependencies of static libraries.

In CMake 3.16 and below the interface link properties attached to libraries are not propagated for private dependencies of static libraries. Only the libraries themselves are propagated to link the dependent binary. CMake 3.17 and later prefer to propagate all interface link properties. This policy provides compatibility for projects that have not been updated to expect the new behavior.

The OLD behavior for this policy is to not propagate interface link properties. The NEW behavior of this policy is to propagate interface link properties.

NOTE:

#+end_quote

CMP0098

New in version 3.17.

FindFLEX runs flex in directory CMAKE_CURRENT_BINARY_DIR when executing.

The module provides a FLEX_TARGET macro which generates FLEX output. In CMake 3.16 and below the macro would generate a custom command that runs flex in the current source directory. CMake 3.17 and later prefer to run it in the build directory and use CMAKE_CURRENT_BINARY_DIR as the WORKING_DIRECTORY of its add_custom_command() invocation. This ensures that any implicitly generated file is written relative to the build tree rather than the source tree, unless the generated file is provided as absolute path.

This policy provides compatibility for projects that have not been updated to expect the new behavior.

The OLD behavior for this policy is for FLEX_TARGET to use the current source directory for the WORKING_DIRECTORY and where to generate implicit files. The NEW behavior of this policy is to use the current binary directory for the WORKING_DIRECTORY relative to which implicit files are generated unless provided as absolute path.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.16

CMP0097

New in version 3.16.

ExternalProject_Add() with GIT_SUBMODULES “” initializes no submodules.

The module provides a GIT_SUBMODULES option which controls what submodules to initialize and update. Starting with CMake 3.16, explicitly setting GIT_SUBMODULES to an empty string means no submodules will be initialized or updated.

This policy provides compatibility for projects that have not been updated to expect the new behavior.

The OLD behavior for this policy is for GIT_SUBMODULES when set to an empty string to initialize and update all git submodules. The NEW behavior for this policy is for GIT_SUBMODULES when set to an empty string to initialize and update no git submodules.

This policy was introduced in CMake version 3.16. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike most policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses OLD behavior.

CMP0096

New in version 3.16.

The project() command preserves leading zeros in version components.

When a VERSION <major>[.<minor>[.<patch>[.<tweak>]]]] argument is given to the project() command, it stores the version string in the PROJECT_VERSION variable and stores individual integer version components in PROJECT_VERSION_{MAJOR,MINOR,PATCH,TWEAK} variables (see policy CMP0048). CMake 3.15 and below dropped leading zeros from each component. CMake 3.16 and higher prefer to preserve leading zeros. This policy provides compatibility for projects that have not been updated to expect the new behavior.

The OLD behavior of this policy drops leading zeros in all components, e.g. such that version 1.07.06 becomes 1.7.6. The NEW behavior of this policy preserves the leading zeros in all components, such that version 1.07.06 remains unchanged.

This policy was introduced in CMake version 3.16. Unlike many policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses the OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0095

New in version 3.16.

RPATH entries are properly escaped in the intermediary CMake install script.

In CMake 3.15 and earlier, RPATH entries set via CMAKE_INSTALL_RPATH or via INSTALL_RPATH have not been escaped before being inserted into the cmake_install.cmake script. Dynamic linkers on ELF-based systems (e.g. Linux and FreeBSD) allow certain keywords in RPATH entries, such as ${ORIGIN} (More details are available in the ld.so man pages on those systems). The syntax of these keywords can match CMake’s variable syntax. In order to not be substituted (usually to an empty string) already by the intermediary cmake_install.cmake script, the user had to double-escape such RPATH keywords, e.g. set(CMAKE_INSTALL_RPATH “\\\${ORIGIN}/../lib”). Since the intermediary cmake_install.cmake script is an implementation detail of CMake, CMake 3.16 and later will make sure RPATH entries are inserted literally by escaping any coincidental CMake syntax.

The OLD behavior of this policy is to not escape RPATH entries in the intermediary cmake_install.cmake script. The NEW behavior is to properly escape coincidental CMake syntax in RPATH entries when generating the intermediary cmake_install.cmake script.

This policy was introduced in CMake version 3.16. CMake version 3.22.1 warns when the policy is not set and detected usage of CMake-like syntax and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.15

CMP0094

New in version 3.15.

Modules FindPython3, FindPython2 and FindPython use LOCATION for lookup strategy.

Starting with CMake 3.15, Modules FindPython3, FindPython2 and FindPython set value LOCATION for, respectively, variables Python3_FIND_STRATEGY, Python2_FIND_STRATEGY and Python_FIND_STRATEGY. This policy provides compatibility with projects that expect the legacy behavior.

The OLD behavior for this policy set value VERSION for variables Python3_FIND_STRATEGY, Python2_FIND_STRATEGY and Python_FIND_STRATEGY.

This policy was introduced in CMake version 3.15. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike many policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses the OLD behavior.

NOTE:

#+end_quote

CMP0093

New in version 3.15.

FindBoost reports Boost_VERSION in x.y.z format.

In CMake 3.14 and below the module would report the Boost version number as specified in the preprocessor definition BOOST_VERSION in the boost/version.hpp file. In CMake 3.15 and later it is preferred that the reported version number matches the x.y.z format reported by the CMake package shipped with Boost 1.70.0 and later. The macro value is still reported in the Boost_VERSION_MACRO variable.

The OLD behavior for this policy is for FindBoost to report Boost_VERSION as specified in the preprocessor definition BOOST_VERSION in boost/version.hpp. The NEW behavior for this policy is for FindBoost to report Boost_VERSION in x.y.z format.

NOTE:

#+end_quote

CMP0092

New in version 3.15.

MSVC warning flags are not in CMAKE_<LANG>_FLAGS by default.

When using MSVC-like compilers in CMake 3.14 and below, warning flags like /W3 are added to CMAKE_<LANG>_FLAGS by default. This is problematic for projects that want to choose a different warning level programmatically. In particular, it requires string editing of the CMAKE_<LANG>_FLAGS variables with knowledge of the CMake builtin defaults so they can be replaced.

CMake 3.15 and above prefer to leave out warning flags from the value of CMAKE_<LANG>_FLAGS by default.

This policy provides compatibility with projects that have not been updated to expect the lack of warning flags. The policy setting takes effect as of the first project() or enable_language() command that initializes CMAKE_<LANG>_FLAGS for a given language <LANG>.

NOTE:

#+end_quote

The OLD behavior for this policy is to place MSVC warning flags in the default CMAKE_<LANG>_FLAGS cache entries. The NEW behavior for this policy is to not place MSVC warning flags in the default cache entries.

NOTE:

#+end_quote

CMP0091

New in version 3.15.

MSVC runtime library flags are selected by an abstraction.

Compilers targeting the MSVC ABI have flags to select the MSVC runtime library. Runtime library selection typically varies with build configuration because there is a separate runtime library for Debug builds.

In CMake 3.14 and below, MSVC runtime library selection flags are added to the default CMAKE_<LANG>_FLAGS_<CONFIG> cache entries by CMake automatically. This allows users to edit their cache entries to adjust the flags. However, the presence of such default flags is problematic for projects that want to choose a different runtime library programmatically. In particular, it requires string editing of the CMAKE_<LANG>_FLAGS_<CONFIG> variables with knowledge of the CMake builtin defaults so they can be replaced.

CMake 3.15 and above prefer to leave the MSVC runtime library selection flags out of the default CMAKE_<LANG>_FLAGS_<CONFIG> values and instead offer a first-class abstraction. The CMAKE_MSVC_RUNTIME_LIBRARY variable and MSVC_RUNTIME_LIBRARY target property may be set to select the MSVC runtime library. If they are not set then CMake uses the default value MultiThreaded$<$<CONFIG:Debug>:Debug>DLL which is equivalent to the original flags.

This policy provides compatibility with projects that have not been updated to be aware of the abstraction. The policy setting takes effect as of the first project() or enable_language() command that enables a language whose compiler targets the MSVC ABI.

NOTE:

#+end_quote

The OLD behavior for this policy is to place MSVC runtime library flags in the default CMAKE_<LANG>_FLAGS_<CONFIG> cache entries and ignore the CMAKE_MSVC_RUNTIME_LIBRARY abstraction. The NEW behavior for this policy is to not place MSVC runtime library flags in the default cache entries and use the abstraction instead.

NOTE:

#+end_quote

CMP0090

New in version 3.15.

export(PACKAGE) does not populate package registry by default.

In CMake 3.14 and below the export(PACKAGE) command populated the user package registry by default and users needed to set the CMAKE_EXPORT_NO_PACKAGE_REGISTRY to disable it, e.g. in automated build and packaging environments. Since the user package registry is stored outside the build tree, this side effect should not be enabled by default. Therefore CMake 3.15 and above prefer that export(PACKAGE) does nothing unless an explicit CMAKE_EXPORT_PACKAGE_REGISTRY variable is set to enable it. This policy provides compatibility with projects that have not been updated.

The OLD behavior for this policy is for export(PACKAGE) command to populate the user package registry unless CMAKE_EXPORT_NO_PACKAGE_REGISTRY is enabled. The NEW behavior is for export(PACKAGE) command to do nothing unless the CMAKE_EXPORT_PACKAGE_REGISTRY is enabled.

This policy was introduced in CMake version 3.15. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike most policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses OLD behavior.

NOTE:

#+end_quote

CMP0089

New in version 3.15.

Compiler id for IBM Clang-based XL compilers is now XLClang.

CMake 3.15 and above recognize that IBM’s Clang-based XL compilers that define __ibmxl__ are a new front-end distinct from xlc with a different command line and set of capabilities. CMake now prefers to present this to projects by setting the CMAKE_<LANG>_COMPILER_ID variable to XLClang instead of XL. However, existing projects may assume the compiler id for Clang-based XL is just XL as it was in CMake versions prior to 3.15. Therefore this policy determines for Clang-based XL compilers which compiler id to report in the CMAKE_<LANG>_COMPILER_ID variable after language <LANG> is enabled by the project() or enable_language() command. The policy must be set prior to the invocation of either command.

The OLD behavior for this policy is to use compiler id XL. The NEW behavior for this policy is to use compiler id XLClang.

This policy was introduced in CMake version 3.15. Use the cmake_policy() command to set this policy to OLD or NEW explicitly. Unlike most policies, CMake version 3.22.1 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0089 variable to control the warning.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.14

CMP0088

New in version 3.14.

FindBISON runs bison in CMAKE_CURRENT_BINARY_DIR when executing.

The module provides a BISON_TARGET macro which generates BISON output. In CMake 3.13 and below the macro would generate a custom command that runs bison in the source directory. CMake 3.14 and later prefer to run it in the build directory and use CMAKE_CURRENT_BINARY_DIR as the WORKING_DIRECTORY of its add_custom_command() invocation. This ensures that any implicitly generated file is written to the build tree rather than the source.

This policy provides compatibility for projects that have not been updated to expect the new behavior.

The OLD behavior for this policy is for BISON_TARGET to use the current source directory for the WORKING_DIRECTORY and where to generate implicit files. The NEW behavior of this policy is to use the current binary directory for the WORKING_DIRECTORY and where to generate implicit files.

This policy was introduced in CMake version 3.14. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike most policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses OLD behavior.

NOTE:

#+end_quote

CMP0087

New in version 3.14.

install(CODE) and install(SCRIPT) support generator expressions.

In CMake 3.13 and earlier, install(CODE) and install(SCRIPT) did not evaluate generator expressions. CMake 3.14 and later will evaluate generator expressions for install(CODE) and install(SCRIPT).

The OLD behavior of this policy is for install(CODE) and install(SCRIPT) to not evaluate generator expressions. The NEW behavior is to evaluate generator expressions for install(CODE) and install(SCRIPT).

Note that it is the value of this policy setting at the end of the directory scope that is important, not its setting at the time of the call to install(CODE) or install(SCRIPT). This has implications for calling these commands from places that have their own policy scope but not their own directory scope (e.g. from files brought in via include() rather than add_subdirectory()).

This policy was introduced in CMake version 3.14. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0086

New in version 3.14.

UseSWIG honors SWIG_MODULE_NAME via -module flag.

Starting with CMake 3.14, UseSWIG passes option -module <module_name> to SWIG compiler if the file property SWIG_MODULE_NAME is specified. This policy provides compatibility with projects that expect the legacy behavior.

The OLD behavior for this policy is to never pass -module option. The NEW behavior is to pass -module option to SWIG compiler if SWIG_MODULE_NAME is specified.

NOTE:

#+end_quote

CMP0085

New in version 3.14.

$<IN_LIST:…> handles empty list items.

In CMake 3.13 and lower, the $<IN_LIST:…> generator expression always returned 0 if the first argument was empty, even if the list contained an empty item. This behavior is inconsistent with the IN_LIST behavior of if(), which this generator expression is meant to emulate. CMake 3.14 and later handles this case correctly.

The OLD behavior of this policy is for $<IN_LIST:…> to always return 0 if the first argument is empty. The NEW behavior is to return 1 if the first argument is empty and the list contains an empty item.

NOTE:

#+end_quote

CMP0084

New in version 3.14.

The FindQt module does not exist for find_package().

The existence of FindQt means that for Qt upstream to provide package config files that can be found by find_package(Qt), the consuming project has to explicitly specify find_package(Qt CONFIG). Removing this module gives Qt a path forward for exporting its own config files which can easily be found by consuming projects.

This policy pretends that CMake’s internal FindQt module does not exist for find_package(). If a project really wants to use Qt 3 or 4, it can call find_package(Qt[34]), include(FindQt), or add FindQt to their CMAKE_MODULE_PATH.

The OLD behavior of this policy is for FindQt to exist for find_package(). The NEW behavior is to pretend that it doesn’t exist for find_package().

NOTE:

#+end_quote

CMP0083

New in version 3.14.

To control generation of Position Independent Executable (PIE) or not, some flags are required at link time.

CMake 3.13 and lower did not add these link flags when POSITION_INDEPENDENT_CODE is set.

The OLD behavior for this policy is to not manage PIE link flags. The NEW behavior is to add link flags if POSITION_INDEPENDENT_CODE is set:

Since a given linker may not support PIE flags in all environments in which it is used, it is the project’s responsibility to use the CheckPIESupported module to check for support to ensure that the POSITION_INDEPENDENT_CODE target property for executables will be honored at link time.

This policy was introduced in CMake version 3.14. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike most policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses OLD behavior.

NOTE:

#+end_quote

NOTE:

#+end_quote

Examples

Behave like CMake 3.13 and do not apply any PIE flags at link stage.

#+begin_quote

      cmake_minimum_required(VERSION 3.13)
      project(foo)

      # ...

      add_executable(foo ...)
      set_property(TARGET foo PROPERTY POSITION_INDEPENDENT_CODE TRUE)

#+end_quote

Use the CheckPIESupported module to detect whether PIE is supported by the current linker and environment. Apply PIE flags only if the linker supports them.

#+begin_quote

      cmake_minimum_required(VERSION 3.14) # CMP0083 NEW
      project(foo)

      include(CheckPIESupported)
      check_pie_supported()

      # ...

      add_executable(foo ...)
      set_property(TARGET foo PROPERTY POSITION_INDEPENDENT_CODE TRUE)

#+end_quote

CMP0082

New in version 3.14.

Install rules from add_subdirectory() calls are interleaved with those in caller.

CMake 3.13 and lower ran the install rules from add_subdirectory() after all other install rules, even if add_subdirectory() was called before the other install rules. CMake 3.14 and above prefer to interleave these add_subdirectory() install rules with the others so that they are run in the order they are declared. This policy provides compatibility for projects that have not been updated to expect the new behavior.

The OLD behavior for this policy is to run the install rules from add_subdirectory() after the other install rules. The NEW behavior for this policy is to run all install rules in the order they are declared.

This policy was introduced in CMake version 3.14. Unlike most policies, CMake version 3.22.1 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0082 variable to control the warning.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.13

CMP0081

New in version 3.13.

Relative paths not allowed in LINK_DIRECTORIES target property.

CMake 3.12 and lower allowed the LINK_DIRECTORIES directory property to contain relative paths. The base path for such relative entries is not well defined. CMake 3.13 and later will issue a FATAL_ERROR if the LINK_DIRECTORIES target property (which is initialized by the LINK_DIRECTORIES directory property) contains a relative path.

The OLD behavior for this policy is not to warn about relative paths in the LINK_DIRECTORIES target property. The NEW behavior for this policy is to issue a FATAL_ERROR if LINK_DIRECTORIES contains a relative path.

NOTE:

#+end_quote

CMP0080

New in version 3.13.

BundleUtilities cannot be included at configure time.

The macros provided by BundleUtilities are intended to be invoked at install time rather than at configure time, because they depend on the listed targets already existing at the time they are invoked. If they are invoked at configure time, the targets haven’t been built yet, and the commands will fail.

This policy restricts the inclusion of BundleUtilities to cmake -P style scripts and install rules. Specifically, it looks for the presence of CMAKE_GENERATOR and throws a fatal error if it exists.

The OLD behavior of this policy is to allow BundleUtilities to be included at configure time. The NEW behavior of this policy is to disallow such inclusion.

NOTE:

#+end_quote

CMP0079

New in version 3.13.

target_link_libraries() allows use with targets in other directories.

Prior to CMake 3.13 the target_link_libraries() command did not accept targets not created in the calling directory as its first argument for calls that update the LINK_LIBRARIES of the target itself. It did accidentally accept targets from other directories on calls that only update the INTERFACE_LINK_LIBRARIES, but would simply add entries to the property as if the call were made in the original directory. Thus link interface libraries specified this way were always looked up by generators in the scope of the original target rather than in the scope that called target_link_libraries().

CMake 3.13 now allows the target_link_libraries() command to be called from any directory to add link dependencies and link interface libraries to targets created in other directories. The entries are added to LINK_LIBRARIES and INTERFACE_LINK_LIBRARIES using a special (internal) suffix to tell the generators to look up the names in the calling scope rather than the scope that created the target.

This policy provides compatibility with projects that already use target_link_libraries() with the INTERFACE keyword on a target in another directory to add INTERFACE_LINK_LIBRARIES entries to be looked up in the target’s directory. Such projects should be updated to be aware of the new scoping rules in that case.

The OLD behavior of this policy is to disallow target_link_libraries() calls naming targets from another directory except in the previously accidentally allowed case of using the INTERFACE keyword only. The NEW behavior of this policy is to allow all such calls but use the new scoping rules.

NOTE:

#+end_quote

CMP0078

New in version 3.13.

UseSWIG generates standard target names.

Starting with CMake 3.13, UseSWIG generates now standard target names. This policy provides compatibility with projects that expect the legacy behavior.

The OLD behavior for this policy relies on UseSWIG_TARGET_NAME_PREFERENCE variable that can be used to specify an explicit preference. The value may be one of:

NOTE:

#+end_quote

CMP0077

New in version 3.13.

option() honors normal variables.

The option() command is typically used to create a cache entry to allow users to set the option. However, there are cases in which a normal (non-cached) variable of the same name as the option may be defined by the project prior to calling the option() command. For example, a project that embeds another project as a subdirectory may want to hard-code options of the subproject to build the way it needs.

For historical reasons in CMake 3.12 and below the option() command removes a normal (non-cached) variable of the same name when:

In both of these cases (typically on the first run in a new build tree), the option() command gives the cache entry type BOOL and removes any normal (non-cached) variable of the same name. In the remaining case that the cache entry of the specified name already exists and has a type (typically on later runs in a build tree), the option() command changes nothing and any normal variable of the same name remains set.

In CMake 3.13 and above the option() command prefers to do nothing when a normal variable of the given name already exists. It does not create or update a cache entry or remove the normal variable. The new behavior is consistent between the first and later runs in a build tree. This policy provides compatibility with projects that have not been updated to expect the new behavior.

When the option() command sees a normal variable of the given name:

See CMP0126 for a similar policy for the set(CACHE) command, but note that there are some differences in NEW behavior between the two policies.

This policy was introduced in CMake version 3.13. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly within a project. Use the CMAKE_POLICY_DEFAULT_CMP0077 variable to set the policy for a third-party project in a subdirectory without modifying it.

NOTE:

#+end_quote

CMP0076

New in version 3.13.

The target_sources() command converts relative paths to absolute.

In CMake 3.13 and above, the target_sources() command now converts relative source file paths to absolute paths in the following cases:

A path that begins with a generator expression is always left unmodified.

This policy provides compatibility with projects that have not been updated to expect this behavior. The OLD behavior for this policy is to leave all relative source file paths unmodified. The NEW behavior of this policy is to convert relative paths to absolute according to above rules.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.12

CMP0075

New in version 3.12.

Include file check macros honor CMAKE_REQUIRED_LIBRARIES.

In CMake 3.12 and above, the

now prefer to link the check executable to the libraries listed in the CMAKE_REQUIRED_LIBRARIES variable. This policy provides compatibility with projects that have not been updated to expect this behavior.

The OLD behavior for this policy is to ignore CMAKE_REQUIRED_LIBRARIES in the include file check macros. The NEW behavior of this policy is to honor CMAKE_REQUIRED_LIBRARIES in the include file check macros.

This policy was introduced in CMake version 3.12. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0074

New in version 3.12.

find_package() uses <PackageName>_ROOT variables.

In CMake 3.12 and above the find_package(<PackageName>) command now searches prefixes specified by the <PackageName>_ROOT CMake variable and the <PackageName>_ROOT environment variable. Package roots are maintained as a stack so nested calls to all find_* commands inside find modules and config packages also search the roots as prefixes. This policy provides compatibility with projects that have not been updated to avoid using <PackageName>_ROOT variables for other purposes.

The OLD behavior for this policy is to ignore <PackageName>_ROOT variables. The NEW behavior for this policy is to use <PackageName>_ROOT variables.

NOTE:

#+end_quote

CMP0073

New in version 3.12.

Do not produce legacy _LIB_DEPENDS cache entries.

Ancient CMake versions once used <tgt>_LIB_DEPENDS cache entries to propagate library link dependencies. This has long been done by other means, leaving the export_library_dependencies() command as the only user of these values. That command has long been disallowed by policy CMP0033, but the <tgt>_LIB_DEPENDS cache entries were left for compatibility with possible non-standard uses by projects.

CMake 3.12 and above now prefer to not produce these cache entries at all. This policy provides compatibility with projects that have not been updated to avoid using them.

The OLD behavior for this policy is to set <tgt>_LIB_DEPENDS cache entries. The NEW behavior for this policy is to not set them.

This policy was introduced in CMake version 3.12. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike most policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses OLD behavior.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.11

CMP0072

New in version 3.11.

FindOpenGL prefers GLVND by default when available.

The FindOpenGL module provides an OpenGL::GL target and an OPENGL_LIBRARIES variable for projects to use for legacy GL interfaces. When both a legacy GL library (e.g. libGL.so) and GLVND libraries for OpenGL and GLX (e.g. libOpenGL.so and libGLX.so) are available, the module must choose between them. It documents an OpenGL_GL_PREFERENCE variable that can be used to specify an explicit preference. When no such preference is set, the module must choose a default preference.

CMake 3.11 and above prefer to choose GLVND libraries. This policy provides compatibility with projects that expect the legacy GL library to be used.

The OLD behavior for this policy is to set OpenGL_GL_PREFERENCE to LEGACY. The NEW behavior for this policy is to set OpenGL_GL_PREFERENCE to GLVND.

This policy was introduced in CMake version 3.11. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.10

CMP0071

New in version 3.10.

Let AUTOMOC and AUTOUIC process GENERATED files.

Since version 3.10, CMake processes regular and GENERATED source files in AUTOMOC and AUTOUIC. In earlier CMake versions, only regular source files were processed. GENERATED source files were ignored silently.

This policy affects how source files that are GENERATED get treated in AUTOMOC and AUTOUIC.

The OLD behavior for this policy is to ignore GENERATED source files in AUTOMOC and AUTOUIC.

The NEW behavior for this policy is to process GENERATED source files in AUTOMOC and AUTOUIC just like regular source files.

NOTE:

#+end_quote

Source skip example:

#+begin_quote

      # ...
      set_property(SOURCE /path/to/file1.h PROPERTY SKIP_AUTOMOC ON)
      set_property(SOURCE /path/to/file2.h PROPERTY SKIP_AUTOUIC ON)
      set_property(SOURCE /path/to/file3.h PROPERTY SKIP_AUTOGEN ON)
      # ...

#+end_quote

This policy was introduced in CMake version 3.10. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0070

New in version 3.10.

Define file(GENERATE) behavior for relative paths.

CMake 3.10 and newer define that relative paths given to INPUT and OUTPUT arguments of file(GENERATE) are interpreted relative to the current source and binary directories, respectively. CMake 3.9 and lower did not define any behavior for relative paths but did not diagnose them either and accidentally treated them relative to the process working directory. Policy CMP0070 provides compatibility with projects that used the old undefined behavior.

This policy affects behavior of relative paths given to file(GENERATE). The OLD behavior for this policy is to treat the paths relative to the working directory of CMake. The NEW behavior for this policy is to interpret relative paths with respect to the current source or binary directory of the caller.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.9

CMP0069

New in version 3.9.

INTERPROCEDURAL_OPTIMIZATION is enforced when enabled.

CMake 3.9 and newer prefer to add IPO flags whenever the INTERPROCEDURAL_OPTIMIZATION target property is enabled and produce an error if flags are not known to CMake for the current compiler. Since a given compiler may not support IPO flags in all environments in which it is used, it is now the project’s responsibility to use the CheckIPOSupported module to check for support before enabling the INTERPROCEDURAL_OPTIMIZATION target property. This approach allows a project to conditionally activate IPO when supported. It also allows an end user to set the CMAKE_INTERPROCEDURAL_OPTIMIZATION variable in an environment known to support IPO even if the project does not enable the property.

Since CMake 3.8 and lower only honored INTERPROCEDURAL_OPTIMIZATION for the Intel compiler on Linux, some projects may unconditionally enable the target property. Policy CMP0069 provides compatibility with such projects.

This policy takes effect whenever the IPO property is enabled. The OLD behavior for this policy is to add IPO flags only for Intel compiler on Linux. The NEW behavior for this policy is to add IPO flags for the current compiler or produce an error if CMake does not know the flags.

This policy was introduced in CMake version 3.9. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

Examples

Behave like CMake 3.8 and do not apply any IPO flags except for Intel compiler on Linux:

#+begin_quote

      cmake_minimum_required(VERSION 3.8)
      project(foo)

      # ...

      set_property(TARGET ... PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)

#+end_quote

Use the CheckIPOSupported module to detect whether IPO is supported by the current compiler, environment, and CMake version. Produce a fatal error if support is not available:

#+begin_quote

      cmake_minimum_required(VERSION 3.9) # CMP0069 NEW
      project(foo)

      include(CheckIPOSupported)
      check_ipo_supported()

      # ...

      set_property(TARGET ... PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)

#+end_quote

Apply IPO flags only if compiler supports it:

#+begin_quote

      cmake_minimum_required(VERSION 3.9) # CMP0069 NEW
      project(foo)

      include(CheckIPOSupported)

      # ...

      check_ipo_supported(RESULT result)
      if(result)
        set_property(TARGET ... PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
      endif()

#+end_quote

Apply IPO flags without any checks. This may lead to build errors if IPO is not supported by the compiler in the current environment. Produce an error if CMake does not know IPO flags for the current compiler:

#+begin_quote

      cmake_minimum_required(VERSION 3.9) # CMP0069 NEW
      project(foo)

      # ...

      set_property(TARGET ... PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)

#+end_quote

CMP0068

New in version 3.9.

RPATH settings on macOS do not affect install_name.

CMake 3.9 and newer remove any effect the following settings may have on the install_name of a target on macOS:

Previously, setting BUILD_WITH_INSTALL_RPATH had the effect of setting both the install_name of a target to INSTALL_NAME_DIR and the RPATH to INSTALL_RPATH. In CMake 3.9, it only affects setting of RPATH. However, if one wants INSTALL_NAME_DIR to apply to the target in the build tree, one may set BUILD_WITH_INSTALL_NAME_DIR.

If SKIP_BUILD_RPATH, CMAKE_SKIP_RPATH or CMAKE_SKIP_INSTALL_RPATH were used to strip the directory portion of the install_name of a target, one may set INSTALL_NAME_DIR=“” instead.

The OLD behavior of this policy is to use the RPATH settings for install_name on macOS. The NEW behavior of this policy is to ignore the RPATH settings for install_name on macOS.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.8

CMP0067

New in version 3.8.

Honor language standard in try_compile() source-file signature.

The try_compile() source file signature is intended to allow callers to check whether they will be able to compile a given source file with the current toolchain. In order to match compiler behavior, any language standard mode should match. However, CMake 3.7 and below did not do this. CMake 3.8 and above prefer to honor the language standard settings for C, CXX (C++), and CUDA using the values of the variables:

This policy provides compatibility for projects that do not expect the language standard settings to be used automatically.

The OLD behavior of this policy is to ignore language standard setting variables when generating the try_compile test project. The NEW behavior of this policy is to honor language standard setting variables.

This policy was introduced in CMake version 3.8. Unlike most policies, CMake version 3.22.1 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0067 variable to control the warning.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.7

CMP0066

New in version 3.7.

Honor per-config flags in try_compile() source-file signature.

The source file signature of the try_compile() command uses the value of the CMAKE_<LANG>_FLAGS variable in the test project so that the test compilation works as it would in the main project. However, CMake 3.6 and below do not also honor config-specific compiler flags such as those in the CMAKE_<LANG>_FLAGS_DEBUG variable. CMake 3.7 and above prefer to honor config-specific compiler flags too. This policy provides compatibility for projects that do not expect config-specific compiler flags to be used.

The OLD behavior of this policy is to ignore config-specific flag variables like CMAKE_<LANG>_FLAGS_DEBUG and only use CMake’s built-in defaults for the current compiler and platform.

The NEW behavior of this policy is to honor config-specific flag variabldes like CMAKE_<LANG>_FLAGS_DEBUG.

This policy was introduced in CMake version 3.7. Unlike most policies, CMake version 3.22.1 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0066 variable to control the warning.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.4

CMP0065

New in version 3.4.

Do not add flags to export symbols from executables without the ENABLE_EXPORTS target property.

CMake 3.3 and below, for historical reasons, always linked executables on some platforms with flags like -rdynamic to export symbols from the executables for use by any plugins they may load via dlopen. CMake 3.4 and above prefer to do this only for executables that are explicitly marked with the ENABLE_EXPORTS target property.

The OLD behavior of this policy is to always use the additional link flags when linking executables regardless of the value of the ENABLE_EXPORTS target property.

The NEW behavior of this policy is to only use the additional link flags when linking executables if the ENABLE_EXPORTS target property is set to True.

This policy was introduced in CMake version 3.4. Unlike most policies, CMake version 3.22.1 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0065 variable to control the warning.

NOTE:

#+end_quote

CMP0064

New in version 3.4.

Recognize TEST as a operator for the if() command.

The TEST operator was added to the if() command to determine if a given test name was created by the add_test() command.

The OLD behavior for this policy is to ignore the TEST operator. The NEW behavior is to interpret the TEST operator.

This policy was introduced in CMake version 3.4. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.3

CMP0063

New in version 3.3.

Honor visibility properties for all target types.

The <LANG>_VISIBILITY_PRESET and VISIBILITY_INLINES_HIDDEN target properties affect visibility of symbols during dynamic linking. When first introduced these properties affected compilation of sources only in shared libraries, module libraries, and executables with the ENABLE_EXPORTS property set. This was sufficient for the basic use cases of shared libraries and executables with plugins. However, some sources may be compiled as part of static libraries or object libraries and then linked into a shared library later. CMake 3.3 and above prefer to honor these properties for sources compiled in all target types. This policy preserves compatibility for projects expecting the properties to work only for some target types.

The OLD behavior for this policy is to ignore the visibility properties for static libraries, object libraries, and executables without exports. The NEW behavior for this policy is to honor the visibility properties for all target types.

This policy was introduced in CMake version 3.3. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0062

New in version 3.3.

Disallow install() of export() result.

The export() command generates a file containing Imported Targets, which is suitable for use from the build directory. It is not suitable for installation because it contains absolute paths to buildsystem locations, and is particular to a single build configuration.

The install(EXPORT) generates and installs files which contain Imported Targets. These files are generated with relative paths (unless the user specifies absolute paths), and are designed for multi-configuration use. See Creating Packages for more.

CMake 3.3 no longer allows the use of the install(FILES) command with the result of the export() command.

The OLD behavior for this policy is to allow installing the result of an export() command. The NEW behavior for this policy is not to allow installing the result of an export() command.

NOTE:

#+end_quote

CMP0061

New in version 3.3.

CTest does not by default tell make to ignore errors (-i).

The ctest_build() and build_command() commands no longer generate build commands for Makefile Generators with the -i option. Previously this was done to help build as much of tested projects as possible. However, this behavior is not consistent with other generators and also causes the return code of the make tool to be meaningless.

Of course users may still add this option manually by setting CTEST_BUILD_COMMAND or the MAKECOMMAND cache entry. See the CTest Build Step MakeCommand setting documentation for their effects.

The OLD behavior for this policy is to add -i to make calls in CTest. The NEW behavior for this policy is to not add -i.

This policy was introduced in CMake version 3.3. Unlike most policies, CMake version 3.22.1 does not warn when this policy is not set and simply uses OLD behavior.

NOTE:

#+end_quote

CMP0060

New in version 3.3.

Link libraries by full path even in implicit directories.

Policy CMP0003 was introduced with the intention of always linking library files by full path when a full path is given to the target_link_libraries() command. However, on some platforms (e.g. HP-UX) the compiler front-end adds alternative library search paths for the current architecture (e.g. /usr/lib/<arch> has alternatives to libraries in /usr/lib for the current architecture). On such platforms the find_library() may find a library such as /usr/lib/libfoo.so that does not belong to the current architecture.

Prior to policy CMP0003 projects would still build in such cases because the incorrect library path would be converted to -lfoo on the link line and the linker would find the proper library in the arch-specific search path provided by the compiler front-end implicitly. At the time we chose to remain compatible with such projects by always converting library files found in implicit link directories to -lfoo flags to ask the linker to search for them. This approach allowed existing projects to continue to build while still linking to libraries outside implicit link directories via full path (such as those in the build tree).

CMake does allow projects to override this behavior by using an IMPORTED library target with its IMPORTED_LOCATION property set to the desired full path to a library file. In fact, many Find Modules are learning to provide Imported Targets instead of just the traditional Foo_LIBRARIES variable listing library files. However, this makes the link line generated for a library found by a Find Module depend on whether it is linked through an imported target or not, which is inconsistent. Furthermore, this behavior has been a source of confusion because the generated link line for a library file depends on its location. It is also problematic for projects trying to link statically because flags like -Wl,-Bstatic -lfoo -Wl,-Bdynamic may be used to help the linker select libfoo.a instead of libfoo.so but then leak dynamic linking to following libraries. (See the LINK_SEARCH_END_STATIC target property for a solution typically used for that problem.)

When the special case for libraries in implicit link directories was first introduced the list of implicit link directories was simply hard-coded (e.g. /lib, /usr/lib, and a few others). Since that time, CMake has learned to detect the implicit link directories used by the compiler front-end. If necessary, the find_library() command could be taught to use this information to help find libraries of the proper architecture.

For these reasons, CMake 3.3 and above prefer to drop the special case and link libraries by full path even when they are in implicit link directories. Policy CMP0060 provides compatibility for existing projects.

The OLD behavior for this policy is to ask the linker to search for libraries whose full paths are known to be in implicit link directories. The NEW behavior for this policy is to link libraries by full path even if they are in implicit link directories.

This policy was introduced in CMake version 3.3. Unlike most policies, CMake version 3.22.1 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0060 variable to control the warning.

NOTE:

#+end_quote

CMP0059

New in version 3.3.

Do not treat DEFINITIONS as a built-in directory property.

CMake 3.3 and above no longer make a list of definitions available through the DEFINITIONS directory property. The COMPILE_DEFINITIONS directory property may be used instead.

The OLD behavior for this policy is to provide the list of flags given so far to the add_definitions() command. The NEW behavior is to behave as a normal user-defined directory property.

NOTE:

#+end_quote

CMP0058

New in version 3.3.

Ninja requires custom command byproducts to be explicit.

When an intermediate file generated during the build is consumed by an expensive operation or a large tree of dependents, one may reduce the work needed for an incremental rebuild by updating the file timestamp only when its content changes. With this approach the generation rule must have a separate output file that is always updated with a new timestamp that is newer than any dependencies of the rule so that the build tool re-runs the rule only when the input changes. We refer to the separate output file as a rule’s witness and the generated file as a rule’s byproduct.

Byproducts may not be listed as outputs because their timestamps are allowed to be older than the inputs. No build tools (like make) that existed when CMake was designed have a way to express byproducts. Therefore CMake versions prior to 3.2 had no way to specify them. Projects typically left byproducts undeclared in the rules that generate them. For example:

#+begin_quote

      add_custom_command(
        OUTPUT witness.txt
        COMMAND ${CMAKE_COMMAND} -E copy_if_different
                ${CMAKE_CURRENT_SOURCE_DIR}/input.txt
                byproduct.txt # timestamp may not change
        COMMAND ${CMAKE_COMMAND} -E touch witness.txt
        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/input.txt
        )
      add_custom_target(Provider DEPENDS witness.txt)
      add_custom_command(
        OUTPUT generated.c
        COMMAND expensive-task -i byproduct.txt -o generated.c
        DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/byproduct.txt
        )
      add_library(Consumer generated.c)
      add_dependencies(Consumer Provider)

#+end_quote

This works well for all generators except Ninja. The Ninja build tool sees a rule listing byproduct.txt as a dependency and no rule listing it as an output. Ninja then complains that there is no way to satisfy the dependency and stops building even though there are order-only dependencies that ensure byproduct.txt will exist before its consumers need it. See discussion of this problem in Ninja Issue 760 for further details on why Ninja works this way.

Instead of leaving byproducts undeclared in the rules that generate them, Ninja expects byproducts to be listed along with other outputs. Such rules may be marked with a restat option that tells Ninja to check the timestamps of outputs after the rules run. This prevents byproducts whose timestamps do not change from causing their dependents to re-build unnecessarily.

Since the above approach does not tell CMake what custom command generates byproduct.txt, the Ninja generator does not have enough information to add the byproduct as an output of any rule. CMake 2.8.12 and above work around this problem and allow projects using the above approach to build by generating phony build rules to tell Ninja to tolerate such missing files. However, this workaround prevents Ninja from diagnosing a dependency that is really missing. It also works poorly in in-source builds where every custom command dependency, even on source files, needs to be treated this way because CMake does not have enough information to know which files are generated as byproducts of custom commands.

CMake 3.2 introduced the BYPRODUCTS option to the add_custom_command() and add_custom_target() commands. This option allows byproducts to be specified explicitly:

#+begin_quote

      add_custom_command(
        OUTPUT witness.txt
        BYPRODUCTS byproduct.txt # explicit byproduct specification
        COMMAND ${CMAKE_COMMAND} -E copy_if_different
                ${CMAKE_CURRENT_SOURCE_DIR}/input.txt
                byproduct.txt # timestamp may not change
      ...

#+end_quote

The BYPRODUCTS option is used by the Ninja generator to list byproducts among the outputs of the custom commands that generate them, and is ignored by other generators.

CMake 3.3 and above prefer to require projects to specify custom command byproducts explicitly so that it can avoid using the phony rule workaround altogether. Policy CMP0058 was introduced to provide compatibility with existing projects that still need the workaround.

This policy has no effect on generators other than Ninja. The OLD behavior for this policy is to generate Ninja phony rules for unknown dependencies in the build tree. The NEW behavior for this policy is to not generate these and instead require projects to specify custom command BYPRODUCTS explicitly.

This policy was introduced in CMake version 3.3. CMake version 3.22.1 warns when it sees unknown dependencies in out-of-source build trees if the policy is not set and then uses OLD behavior. Use the cmake_policy() command to set the policy to OLD or NEW explicitly. The policy setting must be in scope at the end of the top-level CMakeLists.txt file of the project and has global effect.

NOTE:

#+end_quote

CMP0057

New in version 3.3.

Support new if() IN_LIST operator.

CMake 3.3 adds support for the new IN_LIST operator.

The OLD behavior for this policy is to ignore the IN_LIST operator. The NEW behavior is to interpret the IN_LIST operator.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.2

CMP0056

New in version 3.2.

Honor link flags in try_compile() source-file signature.

The try_compile() command source-file signature generates a CMakeLists.txt file to build the source file into an executable. In order to compile the source the same way as it might be compiled by the calling project, the generated project sets the value of the CMAKE_<LANG>_FLAGS variable to that in the calling project. The value of the CMAKE_EXE_LINKER_FLAGS variable may be needed in some cases too, but CMake 3.1 and lower did not set it in the generated project. CMake 3.2 and above prefer to set it so that linker flags are honored as well as compiler flags. This policy provides compatibility with the pre-3.2 behavior.

The OLD behavior for this policy is to not set the value of the CMAKE_EXE_LINKER_FLAGS variable in the generated test project. The NEW behavior for this policy is to set the value of the CMAKE_EXE_LINKER_FLAGS variable in the test project to the same as it is in the calling project.

If the project code does not set the policy explicitly, users may set it on the command line by defining the CMAKE_POLICY_DEFAULT_CMP0056 variable in the cache.

This policy was introduced in CMake version 3.2. Unlike most policies, CMake version 3.22.1 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0056 variable to control the warning.

NOTE:

#+end_quote

CMP0055

New in version 3.2.

Strict checking for the break() command.

CMake 3.1 and lower allowed calls to the break() command outside of a loop context and also ignored any given arguments. This was undefined behavior.

The OLD behavior for this policy is to allow break() to be placed outside of loop contexts and ignores any arguments. The NEW behavior for this policy is to issue an error if a misplaced break or any arguments are found.

This policy was introduced in CMake version 3.2. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.1

CMP0054

New in version 3.1.

Only interpret if() arguments as variables or keywords when unquoted.

CMake 3.1 and above no longer implicitly dereference variables or interpret keywords in an if() command argument when it is a Quoted Argument or a Bracket Argument.

The OLD behavior for this policy is to dereference variables and interpret keywords even if they are quoted or bracketed. The NEW behavior is to not dereference variables or interpret keywords that have been quoted or bracketed.

Given the following partial example:

#+begin_quote

      set(A E)
      set(E "")

      if("${A}" STREQUAL "")
        message("Result is TRUE before CMake 3.1 or when CMP0054 is OLD")
      else()
        message("Result is FALSE in CMake 3.1 and above if CMP0054 is NEW")
      endif()

#+end_quote

After explicit expansion of variables this gives:

#+begin_quote

      if("E" STREQUAL "")

#+end_quote

With the policy set to OLD implicit expansion reduces this semantically to:

#+begin_quote

      if("" STREQUAL "")

#+end_quote

With the policy set to NEW the quoted arguments will not be further dereferenced:

#+begin_quote

      if("E" STREQUAL "")

#+end_quote

This policy was introduced in CMake version 3.1. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0053

New in version 3.1.

Simplify variable reference and escape sequence evaluation.

CMake 3.1 introduced a much faster implementation of evaluation of the Variable References and Escape Sequences documented in the cmake-language(7) manual. While the behavior is identical to the legacy implementation in most cases, some corner cases were cleaned up to simplify the behavior. Specifically:

The setting of policy CMP0010 is not considered, so improper variable reference syntax is always an error.
More characters are allowed to be escaped in variable names. Previously, only ()#“ \@^ were valid characters to escape. Now any non-alphanumeric, non-semicolon, non-NUL character may be escaped following the escape_identity production in the Escape Sequences section of the cmake-language(7) manual.

#+end_quote

The OLD behavior for this policy is to honor the legacy behavior for variable references and escape sequences. The NEW behavior is to use the simpler variable expansion and escape sequence evaluation rules.

NOTE:

#+end_quote

CMP0052

New in version 3.1.

Reject source and build dirs in installed INTERFACE_INCLUDE_DIRECTORIES.

CMake 3.0 and lower allowed subdirectories of the source directory or build directory to be in the INTERFACE_INCLUDE_DIRECTORIES of installed and exported targets, if the directory was also a subdirectory of the installation prefix. This makes the installation depend on the existence of the source dir or binary dir, and the installation will be broken if either are removed after installation.

See Include Directories and Usage Requirements for more on specifying include directories for targets.

The OLD behavior for this policy is to export the content of the INTERFACE_INCLUDE_DIRECTORIES with the source or binary directory. The NEW behavior for this policy is to issue an error if such a directory is used.

NOTE:

#+end_quote

CMP0051

New in version 3.1.

List TARGET_OBJECTS in SOURCES target property.

CMake 3.0 and lower did not include the TARGET_OBJECTS generator expression when returning the SOURCES target property.

Configure-time CMake code is not able to handle generator expressions. If using the SOURCES target property at configure time, it may be necessary to first remove generator expressions using the string(GENEX_STRIP) command. Generate-time CMake code such as file(GENERATE) can handle the content without stripping.

The OLD behavior for this policy is to omit TARGET_OBJECTS expressions from the SOURCES target property. The NEW behavior for this policy is to include TARGET_OBJECTS expressions in the output.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 3.0

CMP0050

Disallow add_custom_command SOURCE signatures.

CMake 2.8.12 and lower allowed a signature for add_custom_command() which specified an input to a command. This was undocumented behavior. Modern use of CMake associates custom commands with their output, rather than their input.

The OLD behavior for this policy is to allow the use of add_custom_command() SOURCE signatures. The NEW behavior for this policy is to issue an error if such a signature is used.

This policy was introduced in CMake version 3.0. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0049

Do not expand variables in target source entries.

CMake 2.8.12 and lower performed an extra layer of variable expansion when evaluating source file names:

#+begin_quote

      set(a_source foo.c)
      add_executable(foo \${a_source})

#+end_quote

This was undocumented behavior.

The OLD behavior for this policy is to expand such variables when processing the target sources. The NEW behavior for this policy is to issue an error if such variables need to be expanded.

NOTE:

#+end_quote

CMP0048

The project() command manages VERSION variables.

CMake version 3.0 introduced the VERSION option of the project() command to specify a project version as well as the name. In order to keep PROJECT_VERSION and related variables consistent with variable PROJECT_NAME it is necessary to set the VERSION variables to the empty string when no VERSION is given to project(). However, this can change behavior for existing projects that set VERSION variables themselves since project() may now clear them. This policy controls the behavior for compatibility with such projects.

The OLD behavior for this policy is to leave VERSION variables untouched. The NEW behavior for this policy is to set VERSION as documented by the project() command.

NOTE:

#+end_quote

CMP0047

Use QCC compiler id for the qcc drivers on QNX.

CMake 3.0 and above recognize that the QNX qcc compiler driver is different from the GNU compiler. CMake now prefers to present this to projects by setting the CMAKE_<LANG>_COMPILER_ID variable to QCC instead of GNU. However, existing projects may assume the compiler id for QNX qcc is just GNU as it was in CMake versions prior to 3.0. Therefore this policy determines for QNX qcc which compiler id to report in the CMAKE_<LANG>_COMPILER_ID variable after language <LANG> is enabled by the project() or enable_language() command. The policy must be set prior to the invocation of either command.

The OLD behavior for this policy is to use the GNU compiler id for the qcc and QCC compiler drivers. The NEW behavior for this policy is to use the QCC compiler id for those drivers.

This policy was introduced in CMake version 3.0. Use the cmake_policy() command to set this policy to OLD or NEW explicitly. Unlike most policies, CMake version 3.22.1 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0047 variable to control the warning.

NOTE:

#+end_quote

CMP0046

Error on non-existent dependency in add_dependencies.

CMake 2.8.12 and lower silently ignored non-existent dependencies listed in the add_dependencies() command.

The OLD behavior for this policy is to silently ignore non-existent dependencies. The NEW behavior for this policy is to report an error if non-existent dependencies are listed in the add_dependencies() command.

NOTE:

#+end_quote

CMP0045

Error on non-existent target in get_target_property.

In CMake 2.8.12 and lower, the get_target_property() command accepted a non-existent target argument without issuing any error or warning. The result variable is set to a -NOTFOUND value.

The OLD behavior for this policy is to issue no warning and set the result variable to a -NOTFOUND value. The NEW behavior for this policy is to issue a FATAL_ERROR if the command is called with a non-existent target.

NOTE:

#+end_quote

CMP0044

Case sensitive <LANG>_COMPILER_ID generator expressions

CMake 2.8.12 introduced the <LANG>_COMPILER_ID generator expressions to allow comparison of the CMAKE_<LANG>_COMPILER_ID with a test value. The possible valid values are lowercase, but the comparison with the test value was performed case-insensitively.

The OLD behavior for this policy is to perform a case-insensitive comparison with the value in the <LANG>_COMPILER_ID expression. The NEW behavior for this policy is to perform a case-sensitive comparison with the value in the <LANG>_COMPILER_ID expression.

NOTE:

#+end_quote

CMP0043

Ignore COMPILE_DEFINITIONS_<Config> properties

CMake 2.8.12 and lower allowed setting the COMPILE_DEFINITIONS_<CONFIG> target property and COMPILE_DEFINITIONS_<CONFIG> directory property to apply configuration-specific compile definitions.

Since CMake 2.8.10, the COMPILE_DEFINITIONS property has supported generator expressions for setting configuration-dependent content. The continued existence of the suffixed variables is redundant, and causes a maintenance burden. Population of the COMPILE_DEFINITIONS_DEBUG property may be replaced with a population of COMPILE_DEFINITIONS directly or via target_compile_definitions():

#+begin_quote

      # Old Interfaces:
      set_property(TARGET tgt APPEND PROPERTY
        COMPILE_DEFINITIONS_DEBUG DEBUG_MODE
      )
      set_property(DIRECTORY APPEND PROPERTY
        COMPILE_DEFINITIONS_DEBUG DIR_DEBUG_MODE
      )

      # New Interfaces:
      set_property(TARGET tgt APPEND PROPERTY
        COMPILE_DEFINITIONS $<$<CONFIG:Debug>:DEBUG_MODE>
      )
      target_compile_definitions(tgt PRIVATE $<$<CONFIG:Debug>:DEBUG_MODE>)
      set_property(DIRECTORY APPEND PROPERTY
        COMPILE_DEFINITIONS $<$<CONFIG:Debug>:DIR_DEBUG_MODE>
      )

#+end_quote

The OLD behavior for this policy is to consume the content of the suffixed COMPILE_DEFINITIONS_<CONFIG> target property when generating the compilation command. The NEW behavior for this policy is to ignore the content of the COMPILE_DEFINITIONS_<CONFIG> target property .

NOTE:

#+end_quote

CMP0042

MACOSX_RPATH is enabled by default.

CMake 2.8.12 and newer has support for using @rpath in a target’s install name. This was enabled by setting the target property MACOSX_RPATH. The @rpath in an install name is a more flexible and powerful mechanism than @executable_path or @loader_path for locating shared libraries.

CMake 3.0 and later prefer this property to be ON by default. Projects wanting @rpath in a target’s install name may remove any setting of the INSTALL_NAME_DIR and CMAKE_INSTALL_NAME_DIR variables.

NOTE:

#+end_quote

CMP0041

Error on relative include with generator expression.

Diagnostics in CMake 2.8.12 and lower silently ignored an entry in the INTERFACE_INCLUDE_DIRECTORIES of a target if it contained a generator expression at any position.

The path entries in that target property should not be relative. High-level API should ensure that by adding either a source directory or a install directory prefix, as appropriate.

As an additional diagnostic, the INTERFACE_INCLUDE_DIRECTORIES generated on an IMPORTED target for the install location should not contain paths in the source directory or the build directory.

The OLD behavior for this policy is to ignore relative path entries if they contain a generator expression. The NEW behavior for this policy is to report an error if a generator expression appears in another location and the path is relative.

NOTE:

#+end_quote

CMP0040

The target in the TARGET signature of add_custom_command() must exist and must be defined in the current directory.

CMake 2.8.12 and lower silently ignored a custom command created with the TARGET signature of add_custom_command() if the target is unknown or was defined outside the current directory.

The OLD behavior for this policy is to ignore custom commands for unknown targets. The NEW behavior for this policy is to report an error if the target referenced in add_custom_command() is unknown or was defined outside the current directory.

NOTE:

#+end_quote

CMP0039

Utility targets may not have link dependencies.

CMake 2.8.12 and lower allowed using utility targets in the left hand side position of the target_link_libraries() command. This is an indicator of a bug in user code.

The OLD behavior for this policy is to ignore attempts to set the link libraries of utility targets. The NEW behavior for this policy is to report an error if an attempt is made to set the link libraries of a utility target.

NOTE:

#+end_quote

CMP0038

Targets may not link directly to themselves.

CMake 2.8.12 and lower allowed a build target to link to itself directly with a target_link_libraries() call. This is an indicator of a bug in user code.

The OLD behavior for this policy is to ignore targets which list themselves in their own link implementation. The NEW behavior for this policy is to report an error if a target attempts to link to itself.

NOTE:

#+end_quote

CMP0037

Target names should not be reserved and should match a validity pattern.

CMake 2.8.12 and lower allowed creating targets using add_library(), add_executable() and add_custom_target() with unrestricted choice for the target name. Newer cmake features such as cmake-generator-expressions(7) and some diagnostics expect target names to match a restricted pattern.

Target names may contain upper and lower case letters, numbers, the underscore character (_), dot(.), plus(+) and minus(-). As a special case, ALIAS and IMPORTED targets may contain two consecutive colons.

Target names reserved by one or more CMake generators are not allowed. Among others these include all, clean, help, and install.

Target names associated with optional features, such as test and package, may also be reserved. CMake 3.10 and below always reserve them. CMake 3.11 and above reserve them only when the corresponding feature is enabled (e.g. by including the CTest or CPack modules).

The OLD behavior for this policy is to allow creating targets with reserved names or which do not match the validity pattern. The NEW behavior for this policy is to report an error if an add_* command is used with an invalid target name.

NOTE:

#+end_quote

CMP0036

The build_name() command should not be called.

This command was added in May 2001 to compute a name for the current operating system and compiler combination. The command has long been documented as discouraged and replaced by the CMAKE_SYSTEM and CMAKE_<LANG>_COMPILER variables.

CMake >= 3.0 prefer that this command never be called. The OLD behavior for this policy is to allow the command to be called. The NEW behavior for this policy is to issue a FATAL_ERROR when the command is called.

NOTE:

#+end_quote

CMP0035

The variable_requires() command should not be called.

This command was introduced in November 2001 to perform some conditional logic. It has long been replaced by the if() command.

NOTE:

#+end_quote

CMP0034

The utility_source() command should not be called.

This command was introduced in March 2001 to help build executables used to generate other files. This approach has long been replaced by add_executable() combined with add_custom_command().

NOTE:

#+end_quote

CMP0033

The export_library_dependencies() command should not be called.

This command was added in January 2003 to export <tgt>_LIB_DEPENDS internal CMake cache entries to a file for installation with a project. This was used at the time to allow transitive link dependencies to work for applications outside of the original build tree of a project. The functionality has been superseded by the export() and install(EXPORT) commands.

NOTE:

#+end_quote

CMP0032

The output_required_files() command should not be called.

This command was added in June 2001 to expose the then-current CMake implicit dependency scanner. CMake’s real implicit dependency scanner has evolved since then but is not exposed through this command. The scanning capabilities of this command are very limited and this functionality is better achieved through dedicated outside tools.

NOTE:

#+end_quote

CMP0031

The load_command() command should not be called.

This command was added in August 2002 to allow projects to add arbitrary commands implemented in C or C++. However, it does not work when the toolchain in use does not match the ABI of the CMake process. It has been mostly superseded by the macro() and function() commands.

NOTE:

#+end_quote

CMP0030

The use_mangled_mesa() command should not be called.

This command was created in September 2001 to support VTK before modern CMake language and custom command capabilities. VTK has not used it in years.

NOTE:

#+end_quote

CMP0029

The subdir_depends() command should not be called.

The implementation of this command has been empty since December 2001 but was kept in CMake for compatibility for a long time.

NOTE:

#+end_quote

CMP0028

Double colon in target name means ALIAS or IMPORTED target.

CMake 2.8.12 and lower allowed the use of targets and files with double colons in target_link_libraries(), with some buildsystem generators.

The use of double-colons is a common pattern used to namespace IMPORTED targets and ALIAS targets. When computing the link dependencies of a target, the name of each dependency could either be a target, or a file on disk. Previously, if a target was not found with a matching name, the name was considered to refer to a file on disk. This can lead to confusing error messages if there is a typo in what should be a target name.

The OLD behavior for this policy is to search for targets, then files on disk, even if the search term contains double-colons. The NEW behavior for this policy is to issue a FATAL_ERROR if a link dependency contains double-colons but is not an IMPORTED target or an ALIAS target.

NOTE:

#+end_quote

CMP0027

Conditionally linked imported targets with missing include directories.

CMake 2.8.11 introduced introduced the concept of INTERFACE_INCLUDE_DIRECTORIES, and a check at cmake time that the entries in the INTERFACE_INCLUDE_DIRECTORIES of an IMPORTED target actually exist. CMake 2.8.11 also introduced generator expression support in the target_link_libraries() command. However, if an imported target is linked as a result of a generator expression evaluation, the entries in the INTERFACE_INCLUDE_DIRECTORIES of that target were not checked for existence as they should be.

The OLD behavior of this policy is to report a warning if an entry in the INTERFACE_INCLUDE_DIRECTORIES of a generator-expression conditionally linked IMPORTED target does not exist.

The NEW behavior of this policy is to report an error if an entry in the INTERFACE_INCLUDE_DIRECTORIES of a generator-expression conditionally linked IMPORTED target does not exist.

NOTE:

#+end_quote

CMP0026

Disallow use of the LOCATION property for build targets.

CMake 2.8.12 and lower allowed reading the LOCATION target property (and configuration-specific variants) to determine the eventual location of build targets. This relies on the assumption that all necessary information is available at configure-time to determine the final location and filename of the target. However, this property is not fully determined until later at generate-time. At generate time, the $<TARGET_FILE> generator expression can be used to determine the eventual LOCATION of a target output.

Code which reads the LOCATION target property can be ported to use the $<TARGET_FILE> generator expression together with the file(GENERATE) subcommand to generate a file containing the target location.

The OLD behavior for this policy is to allow reading the LOCATION properties from build-targets. The NEW behavior for this policy is to not to allow reading the LOCATION properties from build-targets.

NOTE:

#+end_quote

CMP0025

Compiler id for Apple Clang is now AppleClang.

CMake 3.0 and above recognize that Apple Clang is a different compiler than upstream Clang and that they have different version numbers. CMake now prefers to present this to projects by setting the CMAKE_<LANG>_COMPILER_ID variable to AppleClang instead of Clang. However, existing projects may assume the compiler id for Apple Clang is just Clang as it was in CMake versions prior to 3.0. Therefore this policy determines for Apple Clang which compiler id to report in the CMAKE_<LANG>_COMPILER_ID variable after language <LANG> is enabled by the project() or enable_language() command. The policy must be set prior to the invocation of either command.

The OLD behavior for this policy is to use compiler id Clang. The NEW behavior for this policy is to use compiler id AppleClang.

NOTE:

#+end_quote

CMP0024

Disallow include export result.

CMake 2.8.12 and lower allowed use of the include() command with the result of the export() command. This relies on the assumption that the export() command has an immediate effect at configure-time during a cmake run. Certain properties of targets are not fully determined until later at generate-time, such as the link language and complete list of link libraries. Future refactoring will change the effect of the export() command to be executed at generate-time. Use ALIAS targets instead in cases where the goal is to refer to targets by another name.

The OLD behavior for this policy is to allow including the result of an export() command. The NEW behavior for this policy is not to allow including the result of an export() command.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 2.8

CMP0023

Plain and keyword target_link_libraries() signatures cannot be mixed.

CMake 2.8.12 introduced the target_link_libraries() signature using the PUBLIC, PRIVATE, and INTERFACE keywords to generalize the LINK_PUBLIC and LINK_PRIVATE keywords introduced in CMake 2.8.7. Use of signatures with any of these keywords sets the link interface of a target explicitly, even if empty. This produces confusing behavior when used in combination with the historical behavior of the plain target_link_libraries() signature. For example, consider the code:

#+begin_quote

      target_link_libraries(mylib A)
      target_link_libraries(mylib PRIVATE B)

#+end_quote

After the first line the link interface has not been set explicitly so CMake would use the link implementation, A, as the link interface. However, the second line sets the link interface to empty. In order to avoid this subtle behavior CMake now prefers to disallow mixing the plain and keyword signatures of target_link_libraries() for a single target.

The OLD behavior for this policy is to allow keyword and plain target_link_libraries() signatures to be mixed. The NEW behavior for this policy is to not to allow mixing of the keyword and plain signatures.

This policy was introduced in CMake version 2.8.12. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0022

INTERFACE_LINK_LIBRARIES defines the link interface.

CMake 2.8.11 constructed the ’link interface’ of a target from properties matching (IMPORTED_)?LINK_INTERFACE_LIBRARIES(_<CONFIG>)?. The modern way to specify config-sensitive content is to use generator expressions and the IMPORTED_ prefix makes uniform processing of the link interface with generator expressions impossible. The INTERFACE_LINK_LIBRARIES target property was introduced as a replacement in CMake 2.8.12. This new property is named consistently with the INTERFACE_COMPILE_DEFINITIONS, INTERFACE_INCLUDE_DIRECTORIES and INTERFACE_COMPILE_OPTIONS properties. For in-build targets, CMake will use the INTERFACE_LINK_LIBRARIES property as the source of the link interface only if policy CMP0022 is NEW. When exporting a target which has this policy set to NEW, only the INTERFACE_LINK_LIBRARIES property will be processed and generated for the IMPORTED target by default. A new option to the install(EXPORT) and export commands allows export of the old-style properties for compatibility with downstream users of CMake versions older than 2.8.12. The target_link_libraries() command will no longer populate the properties matching LINK_INTERFACE_LIBRARIES(_<CONFIG>)? if this policy is NEW.

Warning-free future-compatible code which works with CMake 2.8.7 onwards can be written by using the LINK_PRIVATE and LINK_PUBLIC keywords of target_link_libraries().

The OLD behavior for this policy is to ignore the INTERFACE_LINK_LIBRARIES property for in-build targets. The NEW behavior for this policy is to use the INTERFACE_LINK_LIBRARIES property for in-build targets, and ignore the old properties matching (IMPORTED_)?LINK_INTERFACE_LIBRARIES(_<CONFIG>)?.

NOTE:

#+end_quote

CMP0021

Fatal error on relative paths in INCLUDE_DIRECTORIES target property.

CMake 2.8.10.2 and lower allowed the INCLUDE_DIRECTORIES target property to contain relative paths. The base path for such relative entries is not well defined. CMake 2.8.12 issues a FATAL_ERROR if the INCLUDE_DIRECTORIES property contains a relative path.

The OLD behavior for this policy is not to warn about relative paths in the INCLUDE_DIRECTORIES target property. The NEW behavior for this policy is to issue a FATAL_ERROR if INCLUDE_DIRECTORIES contains a relative path.

NOTE:

#+end_quote

CMP0020

Automatically link Qt executables to qtmain target on Windows.

CMake 2.8.10 and lower required users of Qt to always specify a link dependency to the qtmain.lib static library manually on Windows. CMake 2.8.11 gained the ability to evaluate generator expressions while determining the link dependencies from IMPORTED targets. This allows CMake itself to automatically link executables which link to Qt to the qtmain.lib library when using IMPORTED Qt targets. For applications already linking to qtmain.lib, this should have little impact. For applications which supply their own alternative WinMain implementation and for applications which use the QAxServer library, this automatic linking will need to be disabled as per the documentation.

The OLD behavior for this policy is not to link executables to qtmain.lib automatically when they link to the QtCore IMPORTED target. The NEW behavior for this policy is to link executables to qtmain.lib automatically when they link to QtCore IMPORTED target.

This policy was introduced in CMake version 2.8.11. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0019

Do not re-expand variables in include and link information.

CMake 2.8.10 and lower re-evaluated values given to the include_directories, link_directories, and link_libraries commands to expand any leftover variable references at the end of the configuration step. This was for strict compatibility with VERY early CMake versions because all variable references are now normally evaluated during CMake language processing. CMake 2.8.11 and higher prefer to skip the extra evaluation.

The OLD behavior for this policy is to re-evaluate the values for strict compatibility. The NEW behavior for this policy is to leave the values untouched.

NOTE:

#+end_quote

CMP0018

Ignore CMAKE_SHARED_LIBRARY_<Lang>_FLAGS variable.

CMake 2.8.8 and lower compiled sources in SHARED and MODULE libraries using the value of the undocumented CMAKE_SHARED_LIBRARY_<Lang>_FLAGS platform variable. The variable contained platform-specific flags needed to compile objects for shared libraries. Typically it included a flag such as -fPIC for position independent code but also included other flags needed on certain platforms. CMake 2.8.9 and higher prefer instead to use the POSITION_INDEPENDENT_CODE target property to determine what targets should be position independent, and new undocumented platform variables to select flags while ignoring CMAKE_SHARED_LIBRARY_<Lang>_FLAGS completely.

The default for either approach produces identical compilation flags, but if a project modifies CMAKE_SHARED_LIBRARY_<Lang>_FLAGS from its original value this policy determines which approach to use.

The OLD behavior for this policy is to ignore the POSITION_INDEPENDENT_CODE property for all targets and use the modified value of CMAKE_SHARED_LIBRARY_<Lang>_FLAGS for SHARED and MODULE libraries.

The NEW behavior for this policy is to ignore CMAKE_SHARED_LIBRARY_<Lang>_FLAGS whether it is modified or not and honor the POSITION_INDEPENDENT_CODE target property.

This policy was introduced in CMake version 2.8.9. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0017

Prefer files from the CMake module directory when including from there.

Starting with CMake 2.8.4, if a cmake-module shipped with CMake (i.e. located in the CMake module directory) calls include() or find_package(), the files located in the CMake module directory are preferred over the files in CMAKE_MODULE_PATH. This makes sure that the modules belonging to CMake always get those files included which they expect, and against which they were developed and tested. In all other cases, the files found in CMAKE_MODULE_PATH still take precedence over the ones in the CMake module directory. The OLD behavior is to always prefer files from CMAKE_MODULE_PATH over files from the CMake modules directory.

This policy was introduced in CMake version 2.8.4. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0016

target_link_libraries() reports error if its only argument is not a target.

In CMake 2.8.2 and lower the target_link_libraries() command silently ignored if it was called with only one argument, and this argument wasn’t a valid target. In CMake 2.8.3 and above it reports an error in this case.

This policy was introduced in CMake version 2.8.3. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0015

#+end_quote

In CMake 2.8.0 and lower the link_directories() command passed relative paths unchanged to the linker. In CMake 2.8.1 and above the link_directories() command prefers to interpret relative paths with respect to CMAKE_CURRENT_SOURCE_DIR, which is consistent with include_directories() and other commands. The OLD behavior for this policy is to use relative paths verbatim in the linker command. The NEW behavior for this policy is to convert relative paths to absolute paths by appending the relative path to CMAKE_CURRENT_SOURCE_DIR.

This policy was introduced in CMake version 2.8.1. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0014

Input directories must have CMakeLists.txt.

CMake versions before 2.8 silently ignored missing CMakeLists.txt files in directories referenced by add_subdirectory() or subdirs(), treating them as if present but empty. In CMake 2.8.0 and above this cmake_policy() determines whether or not the case is an error. The OLD behavior for this policy is to silently ignore the problem. The NEW behavior for this policy is to report an error.

This policy was introduced in CMake version 2.8.0. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0013

Duplicate binary directories are not allowed.

CMake 2.6.3 and below silently permitted add_subdirectory() calls to create the same binary directory multiple times. During build system generation files would be written and then overwritten in the build tree and could lead to strange behavior. CMake 2.6.4 and above explicitly detect duplicate binary directories. CMake 2.6.4 always considers this case an error. In CMake 2.8.0 and above this policy determines whether or not the case is an error. The OLD behavior for this policy is to allow duplicate binary directories. The NEW behavior for this policy is to disallow duplicate binary directories with an error.

NOTE:

#+end_quote

CMP0012

if() recognizes numbers and boolean constants.

In CMake versions 2.6.4 and lower the if() command implicitly dereferenced arguments corresponding to variables, even those named like numbers or boolean constants, except for 0 and 1. Numbers and boolean constants such as true, false, yes, no, on, off, y, n, notfound, ignore (all case insensitive) were recognized in some cases but not all. For example, the code if(TRUE) might have evaluated as false. Numbers such as 2 were recognized only in boolean expressions like if(NOT 2) (leading to false) but not as a single-argument like if(2) (also leading to false). Later versions of CMake prefer to treat numbers and boolean constants literally, so they should not be used as variable names.

The OLD behavior for this policy is to implicitly dereference variables named like numbers and boolean constants. The NEW behavior for this policy is to recognize numbers and boolean constants without dereferencing variables with such names.

NOTE:

#+end_quote

POLICIES INTRODUCED BY CMAKE 2.6

CMP0011

Included scripts do automatic cmake_policy() PUSH and POP.

In CMake 2.6.2 and below, CMake Policy settings in scripts loaded by the include() and find_package() commands would affect the includer. Explicit invocations of cmake_policy(PUSH) and cmake_policy(POP) were required to isolate policy changes and protect the includer. While some scripts intend to affect the policies of their includer, most do not. In CMake 2.6.3 and above, include() and find_package() by default PUSH and POP an entry on the policy stack around an included script, but provide a NO_POLICY_SCOPE option to disable it. This policy determines whether or not to imply NO_POLICY_SCOPE for compatibility. The OLD behavior for this policy is to imply NO_POLICY_SCOPE for include() and find_package() commands. The NEW behavior for this policy is to allow the commands to do their default cmake_policy PUSH and POP.

This policy was introduced in CMake version 2.6.3. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0010

Bad variable reference syntax is an error.

In CMake 2.6.2 and below, incorrect variable reference syntax such as a missing close-brace (${FOO) was reported but did not stop processing of CMake code. This policy determines whether a bad variable reference is an error. The OLD behavior for this policy is to warn about the error, leave the string untouched, and continue. The NEW behavior for this policy is to report an error.

If CMP0053 is set to NEW, this policy has no effect and is treated as always being NEW.

NOTE:

#+end_quote

CMP0009

FILE GLOB_RECURSE calls should not follow symlinks by default.

In CMake 2.6.1 and below, file(GLOB_RECURSE) calls would follow through symlinks, sometimes coming up with unexpectedly large result sets because of symlinks to top level directories that contain hundreds of thousands of files.

This policy determines whether or not to follow symlinks encountered during a file(GLOB_RECURSE) call. The OLD behavior for this policy is to follow the symlinks. The NEW behavior for this policy is not to follow the symlinks by default, but only if FOLLOW_SYMLINKS is given as an additional argument to the FILE command.

This policy was introduced in CMake version 2.6.2. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0008

Libraries linked by full-path must have a valid library file name.

In CMake 2.4 and below it is possible to write code like

#+begin_quote

      target_link_libraries(myexe /full/path/to/somelib)

#+end_quote

where somelib is supposed to be a valid library file name such as libsomelib.a or somelib.lib. For Makefile generators this produces an error at build time because the dependency on the full path cannot be found. For Visual Studio Generators IDE and Xcode generators this used to work by accident because CMake would always split off the library directory and ask the linker to search for the library by name (-lsomelib or somelib.lib). Despite the failure with Makefiles, some projects have code like this and build only with Visual Studio and/or Xcode. This version of CMake prefers to pass the full path directly to the native build tool, which will fail in this case because it does not name a valid library file.

This policy determines what to do with full paths that do not appear to name a valid library file. The OLD behavior for this policy is to split the library name from the path and ask the linker to search for it. The NEW behavior for this policy is to trust the given path and pass it directly to the native build tool unchanged.

This policy was introduced in CMake version 2.6.1. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0007

list command no longer ignores empty elements.

This policy determines whether the list command will ignore empty elements in the list. CMake 2.4 and below list commands ignored all empty elements in the list. For example, a;b;;c would have length 3 and not 4. The OLD behavior for this policy is to ignore empty list elements. The NEW behavior for this policy is to correctly count empty elements in a list.

This policy was introduced in CMake version 2.6.0. CMake version 3.22.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.

NOTE:

#+end_quote

CMP0006

Installing MACOSX_BUNDLE targets requires a BUNDLE DESTINATION.

This policy determines whether the install(TARGETS) command must be given a BUNDLE DESTINATION when asked to install a target with the MACOSX_BUNDLE property set. CMake 2.4 and below did not distinguish application bundles from normal executables when installing targets. CMake 2.6 provides a BUNDLE option to the install(TARGETS) command that specifies rules specific to application bundles on the Mac. Projects should use this option when installing a target with the MACOSX_BUNDLE property set.

The OLD behavior for this policy is to fall back to the RUNTIME DESTINATION if a BUNDLE DESTINATION is not given. The NEW behavior for this policy is to produce an error if a bundle target is installed without a BUNDLE DESTINATION.

NOTE:

#+end_quote

CMP0005

Preprocessor definition values are now escaped automatically.

This policy determines whether or not CMake should generate escaped preprocessor definition values added via add_definitions. CMake versions 2.4 and below assumed that only trivial values would be given for macros in add_definitions calls. It did not attempt to escape non-trivial values such as string literals in generated build rules. CMake versions 2.6 and above support escaping of most values, but cannot assume the user has not added escapes already in an attempt to work around limitations in earlier versions.

The OLD behavior for this policy is to place definition values given to add_definitions directly in the generated build rules without attempting to escape anything. The NEW behavior for this policy is to generate correct escapes for all native build tools automatically. See documentation of the COMPILE_DEFINITIONS target property for limitations of the escaping implementation.

NOTE:

#+end_quote

CMP0004

Libraries linked may not have leading or trailing whitespace.

CMake versions 2.4 and below silently removed leading and trailing whitespace from libraries linked with code like

#+begin_quote

      target_link_libraries(myexe " A ")

#+end_quote

This could lead to subtle errors in user projects.

The OLD behavior for this policy is to silently remove leading and trailing whitespace. The NEW behavior for this policy is to diagnose the existence of such whitespace as an error. The setting for this policy used when checking the library names is that in effect when the target is created by an add_executable() or add_library() command.

NOTE:

#+end_quote

CMP0003

Libraries linked via full path no longer produce linker search paths.

This policy affects how libraries whose full paths are NOT known are found at link time, but was created due to a change in how CMake deals with libraries whose full paths are known. Consider the code

#+begin_quote

      target_link_libraries(myexe /path/to/libA.so)

#+end_quote

CMake 2.4 and below implemented linking to libraries whose full paths are known by splitting them on the link line into separate components consisting of the linker search path and the library name. The example code might have produced something like

#+begin_quote

      ... -L/path/to -lA ...

#+end_quote

in order to link to library A. An analysis was performed to order multiple link directories such that the linker would find library A in the desired location, but there are cases in which this does not work. CMake versions 2.6 and above use the more reliable approach of passing the full path to libraries directly to the linker in most cases. The example code now produces something like

#+begin_quote

      ... /path/to/libA.so ....

#+end_quote

Unfortunately this change can break code like

#+begin_quote

      target_link_libraries(myexe /path/to/libA.so B)

#+end_quote

where B is meant to find /path/to/libB.so. This code is wrong because the user is asking the linker to find library B but has not provided a linker search path (which may be added with the link_directories command). However, with the old linking implementation the code would work accidentally because the linker search path added for library A allowed library B to be found.

In order to support projects depending on linker search paths added by linking to libraries with known full paths, the OLD behavior for this policy will add the linker search paths even though they are not needed for their own libraries. When this policy is set to OLD, CMake will produce a link line such as

#+begin_quote

      ... -L/path/to /path/to/libA.so -lB ...

#+end_quote

which will allow library B to be found as it was previously. When this policy is set to NEW, CMake will produce a link line such as

#+begin_quote

      ... /path/to/libA.so -lB ...

#+end_quote

which more accurately matches what the project specified.

The setting for this policy used when generating the link line is that in effect when the target is created by an add_executable or add_library command. For the example described above, the code

#+begin_quote

      cmake_policy(SET CMP0003 OLD) # or cmake_policy(VERSION 2.4)
      add_executable(myexe myexe.c)
      target_link_libraries(myexe /path/to/libA.so B)

#+end_quote

will work and suppress the warning for this policy. It may also be updated to work with the corrected linking approach:

#+begin_quote

      cmake_policy(SET CMP0003 NEW) # or cmake_policy(VERSION 2.6)
      link_directories(/path/to) # needed to find library B
      add_executable(myexe myexe.c)
      target_link_libraries(myexe /path/to/libA.so B)

#+end_quote

Even better, library B may be specified with a full path:

#+begin_quote

      add_executable(myexe myexe.c)
      target_link_libraries(myexe /path/to/libA.so /path/to/libB.so)

#+end_quote

When all items on the link line have known paths CMake does not check this policy so it has no effect.

Note that the warning for this policy will be issued for at most one target. This avoids flooding users with messages for every target when setting the policy once will probably fix all targets.

NOTE:

#+end_quote

CMP0002

Logical target names must be globally unique.

Targets names created with add_executable(), add_library(), or add_custom_target() are logical build target names. Logical target names must be globally unique because:

#+begin_quote

      - Unique names may be referenced unambiguously both in CMake
        code and on make tool command lines.
      - Logical names are used by Xcode and VS IDE generators
        to produce meaningful project names for the targets.

#+end_quote

The logical name of executable and library targets does not have to correspond to the physical file names built. Consider using the OUTPUT_NAME target property to create two targets with the same physical name while keeping logical names distinct. Custom targets must simply have globally unique names (unless one uses the global property ALLOW_DUPLICATE_CUSTOM_TARGETS with a Makefiles generator).

NOTE:

#+end_quote

CMP0001

CMAKE_BACKWARDS_COMPATIBILITY should no longer be used.

The behavior is to check CMAKE_BACKWARDS_COMPATIBILITY and present it to the user. The NEW behavior is to ignore CMAKE_BACKWARDS_COMPATIBILITY completely.

In CMake 2.4 and below the variable CMAKE_BACKWARDS_COMPATIBILITY was used to request compatibility with earlier versions of CMake. In CMake 2.6 and above all compatibility issues are handled by policies and the cmake_policy() command. However, CMake must still check CMAKE_BACKWARDS_COMPATIBILITY for projects written for CMake 2.4 and below.

NOTE:

#+end_quote

CMP0000

A minimum required CMake version must be specified.

CMake requires that projects specify the version of CMake to which they have been written. This policy has been put in place so users trying to build the project may be told when they need to update their CMake. Specifying a version also helps the project build with CMake versions newer than that specified. Use the cmake_minimum_required() command at the top of your main CMakeLists.txt file:

#+begin_quote

      cmake_minimum_required(VERSION <major>.<minor>)

#+end_quote

where <major>.<minor> is the version of CMake you want to support (such as 3.14). The command will ensure that at least the given version of CMake is running and help newer versions be compatible with the project. See documentation of cmake_minimum_required() for details.

Note that the command invocation must appear in the CMakeLists.txt file itself; a call in an included file is not sufficient. However, the cmake_policy() command may be called to set policy CMP0000 to OLD or NEW behavior explicitly. The OLD behavior is to silently ignore the missing invocation. The NEW behavior is to issue an error instead of a warning. An included file may set CMP0000 explicitly to affect how this policy is enforced for the main CMakeLists.txt file.

This policy was introduced in CMake version 2.6.0.

NOTE:

#+end_quote

COPYRIGHT

2000-2021 Kitware, Inc. and Contributors

Information about cmake-policies.7 is found in manpage for: /path/to/libA.so …. /path/to/libA.so B) L/path/to /path/to/libA.so lB … /path/to/libA.so lB … /path/to/libA.so B) /path/to/libA.so B) /path/to/libA.so /path/to/libB.so)

Manpages - cmake-policies.7

Table of Contents

NAME

INTRODUCTION

POLICIES INTRODUCED BY CMAKE 3.22

CMP0128

CMP0127

POLICIES INTRODUCED BY CMAKE 3.21

CMP0126

CMP0125

CMP0124

CMP0123

CMP0122

CMP0121

POLICIES INTRODUCED BY CMAKE 3.20

CMP0120

CMP0119

CMP0118

CMP0117

CMP0116

CMP0115

POLICIES INTRODUCED BY CMAKE 3.19

CMP0114

CMP0113

CMP0112

CMP0111

CMP0110

CMP0109

POLICIES INTRODUCED BY CMAKE 3.18

CMP0108

CMP0107

CMP0106

CMP0105

CMP0104

Examples

CMP0103

POLICIES INTRODUCED BY CMAKE 3.17

CMP0102

CMP0101

CMP0100

CMP0099

CMP0098

POLICIES INTRODUCED BY CMAKE 3.16

CMP0097

CMP0096

CMP0095

POLICIES INTRODUCED BY CMAKE 3.15

CMP0094

CMP0093

CMP0092

CMP0091

CMP0090

CMP0089

POLICIES INTRODUCED BY CMAKE 3.14

CMP0088

CMP0087

CMP0086

CMP0085

CMP0084

CMP0083

Examples

CMP0082

POLICIES INTRODUCED BY CMAKE 3.13

CMP0081

CMP0080

CMP0079

CMP0078

CMP0077

CMP0076

POLICIES INTRODUCED BY CMAKE 3.12

CMP0075

CMP0074

CMP0073

POLICIES INTRODUCED BY CMAKE 3.11

CMP0072

POLICIES INTRODUCED BY CMAKE 3.10

CMP0071

CMP0070

POLICIES INTRODUCED BY CMAKE 3.9

CMP0069