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61 lines
2.8 KiB
ReStructuredText
61 lines
2.8 KiB
ReStructuredText
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CMP0077
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-------
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.. versionadded:: 3.13
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:command:`option` honors normal variables.
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The :command:`option` command is typically used to create a cache entry
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to allow users to set the option. However, there are cases in which a
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normal (non-cached) variable of the same name as the option may be
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defined by the project prior to calling the :command:`option` command.
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For example, a project that embeds another project as a subdirectory
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may want to hard-code options of the subproject to build the way it needs.
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For historical reasons in CMake 3.12 and below the :command:`option`
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command *removes* a normal (non-cached) variable of the same name when:
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* a cache entry of the specified name does not exist at all, or
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* a cache entry of the specified name exists but has not been given
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a type (e.g. via ``-D<name>=ON`` on the command line).
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In both of these cases (typically on the first run in a new build tree),
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the :command:`option` command gives the cache entry type ``BOOL`` and
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removes any normal (non-cached) variable of the same name. In the
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remaining case that the cache entry of the specified name already
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exists and has a type (typically on later runs in a build tree), the
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:command:`option` command changes nothing and any normal variable of
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the same name remains set.
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In CMake 3.13 and above the :command:`option` command prefers to
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do nothing when a normal variable of the given name already exists.
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It does not create or update a cache entry or remove the normal variable.
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The new behavior is consistent between the first and later runs in a
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build tree. This policy provides compatibility with projects that have
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not been updated to expect the new behavior.
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When the :command:`option` command sees a normal variable of the given
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name:
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* The ``OLD`` behavior for this policy is to proceed even when a normal
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variable of the same name exists. If the cache entry does not already
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exist and have a type then it is created and/or given a type and the
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normal variable is removed.
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* The ``NEW`` behavior for this policy is to do nothing when a normal
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variable of the same name exists. The normal variable is not removed.
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The cache entry is not created or updated and is ignored if it exists.
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See :policy:`CMP0126` for a similar policy for the :command:`set(CACHE)`
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command, but note that there are some differences in ``NEW`` behavior
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between the two policies.
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This policy was introduced in CMake version 3.13. CMake version
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|release| warns when the policy is not set and uses ``OLD`` behavior.
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Use the :command:`cmake_policy` command to set it to ``OLD`` or ``NEW``
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explicitly within a project. Use the :variable:`CMAKE_POLICY_DEFAULT_CMP0077
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<CMAKE_POLICY_DEFAULT_CMP\<NNNN\>>` variable to set the policy for
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a third-party project in a subdirectory without modifying it.
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.. include:: DEPRECATED.txt
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