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https://github.com/Kitware/CMake.git
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Raul Tambre
4a0485be7f
The changes are part of CMP0128. When the standard level is unset: * Flags are added if extension mode doesn't match the compiler's default. Previously logic only worked if LANG_EXTENSIONS was ON. Fixes #22224. * The full flag is used. Previously CMAKE_LANG_EXTENSION_COMPILE_OPTION was used. This was only supported for IAR. Otherwise: * Avoid adding flags if not necessary per the detected compiler defaults. * Fixed check for when the requested standard is older. It now matches the nearby comments. I reworded the fallback comment as its logic was a bit difficult to wrap my head around.
79 lines
2.6 KiB
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79 lines
2.6 KiB
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CMP0128
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-------
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.. versionadded:: 3.22
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When this policy is set to ``NEW``:
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* :prop_tgt:`<LANG>_EXTENSIONS` is initialized to
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:variable:`CMAKE_<LANG>_EXTENSIONS_DEFAULT`.
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* Extensions are correctly disabled/enabled if :prop_tgt:`<LANG>_STANDARD` is
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unset.
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* Standard mode-affecting flags aren't added unless necessary to achieve the
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specified mode.
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The ``OLD`` behavior:
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* Initializes :prop_tgt:`<LANG>_EXTENSIONS` to ``ON``.
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* Always adds a flag if :prop_tgt:`<LANG>_STANDARD` is set and
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:prop_tgt:`<LANG>_STANDARD_REQUIRED` is ``OFF``.
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* If :prop_tgt:`<LANG>_STANDARD` is unset:
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* Doesn't disable extensions even if :prop_tgt:`<LANG>_EXTENSIONS` is
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``OFF``.
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* Fails to enable extensions if :prop_tgt:`<LANG>_EXTENSIONS` is ``ON``
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except for the ``IAR`` compiler.
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Code may need to be updated for the ``NEW`` behavior in the following cases:
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* If :prop_tgt:`<LANG>_EXTENSIONS` matches
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:variable:`CMAKE_<LANG>_EXTENSIONS_DEFAULT` or is unset and the compiler's
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default satisfies :prop_tgt:`<LANG>_STANDARD` but the compiled code requires
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the exact standard specified.
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Such code should set :prop_tgt:`<LANG>_STANDARD_REQUIRED` to ``ON``.
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For example:
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.. code-block:: cmake
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cmake_minimum_required(VERSION |release|)
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project(example C)
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add_executable(exe main.c)
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set_property(TARGET exe PROPERTY C_STANDARD 99)
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If the compiler defaults to C11 then the standard specification for C99 is
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satisfied and CMake will pass no flags. ``main.c`` will no longer compile if
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it is incompatible with C11.
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* If a standard mode flag previously overridden by CMake's and not used during
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compiler detection now takes effect due to CMake no longer adding one as the
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default detected is appropriate.
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Such code should be converted to either:
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* Use :prop_tgt:`<LANG>_STANDARD` and :prop_tgt:`<LANG>_EXTENSIONS` instead
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of manually adding flags.
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* Or ensure the manually-specified flags are used during compiler detection.
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If compiler flags affecting the standard mode are used during compiler
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detection (for example in :manual:`a toolchain file <cmake-toolchains(7)>`
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using :variable:`CMAKE_<LANG>_FLAGS_INIT`) then they will affect the detected
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default :variable:`standard <CMAKE_<LANG>_STANDARD_DEFAULT>` and
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:variable:`extensions <CMAKE_<LANG>_EXTENSIONS_DEFAULT>`.
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Unlike many policies, CMake version |release| does *not* warn when the policy
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is not set and simply uses the ``OLD`` behavior. Use the
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:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
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See documentation of the
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:variable:`CMAKE_POLICY_WARNING_CMP0128 <CMAKE_POLICY_WARNING_CMP<NNNN>>`
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variable to control the warning.
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.. include:: DEPRECATED.txt
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