CMP0077

.. versionadded:: 3.13

:command:option honors normal variables.

The :command: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 :command: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 :command:option command removes a normal (non-cached) variable of the same name when:

a cache entry of the specified name does not exist at all, or
a cache entry of the specified name exists but has not been given a type (e.g. via -D<name>=ON on the command line).

In both of these cases (typically on the first run in a new build tree), the :command: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 :command:option command changes nothing and any normal variable of the same name remains set.

In CMake 3.13 and above the :command: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 :command:option command sees a normal variable of the given name:

The OLD behavior for this policy is to proceed even when a normal variable of the same name exists. If the cache entry does not already exist and have a type then it is created and/or given a type and the normal variable is removed.
The NEW behavior for this policy is to do nothing when a normal variable of the same name exists. The normal variable is not removed. The cache entry is not created or updated and is ignored if it exists.

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

.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.13 .. |WARNS_OR_DOES_NOT_WARN| replace:: warns .. include:: include/STANDARD_ADVICE.rst

Use the :variable:CMAKE_POLICY_DEFAULT_CMP0077 <CMAKE_POLICY_DEFAULT_CMP\<NNNN\>> variable to set the policy for a third-party project in a subdirectory without modifying it.

.. include:: include/DEPRECATED.rst