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Help: Make policy CMP0126 wording more accurate

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The OLD behavior only removes a non-cache variable of the same
name in specific circumstances. The previous wording implied
that it would always occur.

Also add a note about the behavior compared to the analogous
CMP0077 policy, which affects the option() command in a similar
but subtly different way.
This commit is contained in:
Craig Scott
2021-07-17 16:27:41 +10:00
parent c4bc250f8c
commit 7b5fa0f7b4
2 changed files with 20 additions and 7 deletions
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4
Help/policy/CMP0077.rst
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@@ -46,6 +46,10 @@ name:
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.
This policy was introduced in CMake version 3.13. CMake version
|release| warns when the policy is not set and uses ``OLD`` behavior.
Use the :command:`cmake_policy` command to set it to ``OLD`` or ``NEW``

23
Help/policy/CMP0126.rst
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@@ -3,16 +3,25 @@ CMP0126
.. versionadded:: 3.21
The :command:`set(CACHE)` does not remove a normal variable of the same name.
When this policy is set to ``NEW``, the :command:`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:
Starting with CMake 3.21, the :command:`set(CACHE)` does not remove, in the
current scope, any normal variable with the same name.
* No cache variable of that name existed previously.
The ``OLD`` behavior for this policy is to have the :command:`set(CACHE)`
command removing the normal variable of the same name, if any. The ``NEW``
behavior for this policy is to keep the normal variable of the same name.
* A cache variable of that name existed previously, but it had no type.
This can occur when the variable was set on the command line using a form
like ``cmake -DMYVAR=blah`` instead of ``cmake -DMYVAR:STRING=blah``.
This policy was introduced in CMake version 3.21. Use the
Note that the ``NEW`` behavior has an important difference to the similar
``NEW`` behavior of policy :policy:`CMP0077`. The :command:`set(CACHE)`
command always sets the cache variable if it did not exist previously,
regardless of the ``CMP0126`` policy setting. The :command:`option` command
will *not* set the cache variable if a non-cache variable of the same name
already exists and :policy:`CMP0077` is set to ``NEW``.
Policy ``CMP0126`` was introduced in CMake version 3.21. Use the
:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
Unlike many policies, CMake version |release| does *not* warn when the policy
is not set and simply uses ``OLD`` behavior. See documentation of the