# 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:

- 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 `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:

- 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 `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 3.27.6 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

The `OLD` behavior of a policy is `deprecated by definition` and may be removed in a future version of CMake.