meson does not search CMake user package registry

[gpanders]

Describe the bug
Users can install CMake packages into the user package registry ($HOME/.cmake/packages on Unix by default). CMake will check this directory for packages if a package isn't found on the system, but meson does not.

To Reproduce

The following works with plain CMake:

$ mkdir -p ~/.cmake/packages/Foo
$ echo "$HOME/cmake/foo" > ~/.cmake/packages/Foo/foo
$ mkdir -p ~/cmake/foo
$ touch ~/cmake/foo/FooConfig.cmake
$ mkdir -p ~/cmake/bar
$ cd ~/cmake/bar
$ cat >CMakeLists.txt <<EOF
project(bar)
find_package(Foo REQUIRED)
EOF
$ cd ~/cmake/bar
$ mkdir build
$ cd build
$ cmake ..

Now trying to use the Foo package from meson:

$ mkdir ~/meson/bar
$ cd ~/meson/bar
$ cat > meson.build <<EOF
project('bar', 'c')

foo = dependency('Foo')
EOF
$ meson build

meson cannot find Foo.

Expected behavior
meson searches the CMake user package registry for CMake packages.

system parameters

• macOS Big Sur
• Python 3.9.7
• meson 0.59.2

[mensinda]

Should be fixed with #9424. However, only for the Linux registry. I am not sure if Meson should even attempt to read/touch the Windows registry in any way.