tests/build_system: add test for relative paths

[basilfx]

Contribution description

Going through the list of (old) issues, I came across #14262. I believe that issue isn't completely relevant anymore, after #18913 got merged.

Nonetheless, #18913 did not add a test, which #14262 did. I think the test still adds value.

Testing procedure

Run make -C tests/build_system/relpath all test and it should pass.

Issues/PRs references

#14262, #18913

Declaration of AI-Tools / LLMs usage:

AI-Tools / LLMs that were used are:

• none

[basilfx]

So if I understand correctly, the difference between #14262 and #18913 is:

• -fmacro-prefix-map - macros only (e.g. __FILE__)
• -fdebug-prefix-map - debug information only
• -ffile-prefix-map - both

[crasbe]

We can close #14262 then, right?

[crasbe]

Suggested change

	which should evaluate to the path of a filename relative to `$(RIOTBASE)`. The
	which should resolve to the path of a filename relative to `$(RIOTBASE)`. The

Perhaps?

[crasbe]

Suggested change

*

That's from riotgen as far as I know, but we can still save a line :)

[crasbe]

Suggested change

[riot-ci]

Murdock results

❌ FAILED

a3846e9 fixup! tests/build_system: add test for relative paths

Success	Failures	Total	Runtime
12	0	19	23s

Artifacts

[basilfx]

This isn't working on CI, because of ccache.

ccache rewrites the path mapping, which results in just main.c instead of tests/build_system/relpath/main.c

When you run the follwing from within tests/build_system/relpath:

BOARD=native64 make clean
BOARD=native64 make all
BOARD=native64 make term

__FILE__: tests/build_system/relpath/main.c

CCACHE=ccache BOARD=native64 make clean
CCACHE=ccache BOARD=native64 make all
CCACHE=ccache BOARD=native64 make term

__FILE__: tests/build_system/relpath/main.c

CCACHE=ccache CCACHE_BASEDIR="$(pwd)" BOARD=native64 make clean
CCACHE=ccache CCACHE_BASEDIR="$(pwd)" BOARD=native64 make all
CCACHE=ccache CCACHE_BASEDIR="$(pwd)" BOARD=native64 make term

__FILE__: main.c

I have two options:

• Close this PR
• Modify the test to only check for a relative answer (main.c is still relative), maybe even based on the presence of CCACHE_BASEDIR.