Building from source fails with cmake version 3.31

[stefanfrede]

I get the following error when trying to build from source:

cmake .

-- Setting build type to default 'RelWithDebInfo'
-- Trying to use PCRE2 from the system
-- Rust Target: x86_64-unknown-linux-gnu
CMake Error at cmake/Tests.cmake:54 (cmake_policy):
  Policy CMP0037 may not be set to OLD behavior because this version of CMake
  no longer supports it.  The policy was introduced in CMake version 3.0.0,
  and use of NEW behavior is now required.

  Please either update your CMakeLists.txt files to conform to the new
  behavior or use an older version of CMake that still supports the old
  behavior.  Run cmake --help-policy CMP0037 for more information.
Call Stack (most recent call first):
  CMakeLists.txt:75 (include)


-- The following features have been enabled:

 * gettext, translate messages with gettext

-- The following OPTIONAL packages have been found:

 * Gettext

-- The following REQUIRED packages have been found:

 * Rust

-- The following features have been disabled:

 * Documentation, user manual and documentation

CMake Error at cmake/Tests.cmake:55 (add_custom_target):
  The target name "test" is reserved when CTest testing is enabled.
Call Stack (most recent call first):
  CMakeLists.txt:75 (include)

The last time I built from source was around Christmas last year and it worked.

[faho]

Gotta love CMake.

They no longer allow you to define a custom "test" target, which means we are now forced to have a broken "test" target.

Run make fish_run_tests instead.

[zanchey]

This probably needs fixing for 4.0. What do you think of keeping make test working for CMake < 3.31 depending on the outcome of cmake_policy(GET CMP0037 TEST_TARGET)?

[faho]

I would just merge the same thing for 4.0

We have two issues with the builtin "test" target:

1. It doesn't depend on the actual executable existing, so if you haven't run make before it'll just fail all the tests
2. It doesn't print any failure output - so if a test fails, you don't actually know why

Of course both of those seem like terrible ideas to me, but since cmake isn't going to allow us to change it anymore, that's what we have.

If the tests are going to pass, tho, and since everyone's going to run make and make test separately anyway, I don't think there's a high priority to fix it for 4.0.

Longer term, I'd want to actually remove cmake and replace it with something else - be that a makefile or just a simple script.

What do you think of keeping make test working for CMake < 3.31 depending on the outcome of cmake_policy(GET CMP0037 TEST_TARGET)?

That means either make test will work properly, or it'll work badly, depending on the cmake version. I'd rather just tell everyone to use the good test target anywhere.