Introduce a mechanism (via the private and undocumented `ISSUE_WARNING`
option to the `cmake_policy` command) to allow built-in modules to issue
policy warnings. Update modules to use this.
This allows modules to issue policy warnings with the `CMD_POLICY`
diagnostic type, which is consistent with internally issued diagnostics.
This also tends to simplify the logic for issuing such warnings in much
the way the helpers introduced in the previous commit did for the C++
code.
Tweak `cmMessenger` to also show the "warning is for project developers"
notice for all diagnostics that are descendants of the `CMD_AUTHOR`
category. When doing so, also show both command-line options which can
suppress the message.
Update expected test output to account for the new format of diagnostic
messages. These changes were applied entirely by `sed` using the
following commands:
- `/Use -Wno-dev to suppress/s/-Wno-dev/-Wno-author/g`
- `s/Warning [\\][(]dev[\\][)]/Warning \\(author\\)/g`
- `s/CMake Deprecation Warning/CMake Warning \\(deprecated\\)/g`
This is not a complete fix, but covers a significant fraction of the
needed changes, and this commit is strictly automated changes.
The OLD behaviors of all policies are deprecated, but only by
documentation. Add an explicit deprecation diagnostic for policies
introduced in CMake 3.27 and below to encourage projects to port
away from setting policies to OLD.
Teach `ExternalProject_Add` and `FetchContent_Declare` to resolve
relative remote URLs provided via `GIT_REPOSITORY`. Add policy
CMP0150 to maintain compatibility.
Fixes: #24211
Co-Authored-By: Craig Scott <craig.scott@crascit.com>