Every policy's documentation has a paragraph on what version of CMake
introduced it, how to set the policy, and whether CMake warns if the
policy is not set. The wording of this paragraph has diverged across
policies over time. Factor the paragraph out into a standard advice
document included by every policy.
Optionally verify that items in `LINK_LIBRARIES` and
`INTERFACE_LINK_LIBRARIES` that can be target names are actually target
names. Add a `LINK_LIBRARIES_ONLY_TARGETS` target property and
corresponding `CMAKE_LINK_LIBRARIES_ONLY_TARGETS` variable to enable
this new check.
Fixes: #22858
The most likely documentation page a project author will read in
response to a policy warning is the page for the policy itself.
Add to every policy documentation page a note explicitly stating
that the OLD behavior is deprecated. Also mention this in the
cmake_policy() command documentation that explains how to set a
policy to OLD.
Suggested-by: Fraser Hutchison <fraser.hutchison@gmail.com>
Starting with 3.0 we will use only two components for the feature level,
and policies are only ever introduced with a bump to the feature level
version.
Introduce a policy to control the behavior.
The AliasTargets unit test already tests that using a
double-semicolon in the name is not an error. Change the ExportImport
test to use a namespace with a double-semicolon too.
Brad King