The test for cm::optional assumed that *opt would return a reference
to a non-constructed object if opt.has_value() is false. However, on
certain systems that build CMake with flags to harden the build,
this condition aborts rather than returning the invalid reference.
Fix this by getting the reference only when the cm::optional is
known to actually have a value.
Fixes: #19964
CMake Tests Directory
*********************
This directory contains the CMake test suite.
See also the `CMake Source Code Guide`_.
.. _`CMake Source Code Guide`: ../Help/dev/source.rst
Many tests exist as immediate subdirectories, but some tests
are organized as follows.
* ``CMakeLib/``:
Source code, used for tests, that links to the ``CMakeLib`` library
defined over in ``Source/``.
* ``CMakeOnly/``:
Deprecated. Tests that run CMake to generate a project but not build it.
Superseded by ``Tests/RunCMake/``.
* ``Find*/``:
Tests for specific find modules that can only be run on machines with
the corresponding packages installed. They are enabled in
``CMakeLists.txt`` by undocumented options used on CI builds.
* ``Module/``:
Tests for specific CMake modules.
* ``RunCMake/``:
Tests that run CMake and/or other tools while precisely checking
their return code and stdout/stderr content. Useful for testing
error cases and diagnostic output.
e8bd920df1