mtest: fix building of all test deps for --suite

The previous commit eb1e52a introduced
a variable `rebuild_only_tests` to fix various edge cases in
rebuild_deps.

In particular, if all tests are selected anyway, rebuild_deps prior
to the introduction of `rebuild_only_tests` would potentially
create a huge list of targets, which may overflow the
ARG_MAX limit.

For that case `rebuild_only_tests` was introduced and is set to an empty list, which means that rebuild_deps falls back to the `meson-test-prereq` ninja target, that already contains the necessary targets.

This is wrong, though, when `meson test` is executed with the "--suite"
option. In that case, the user requested a particular subset of the
tests, but `rebuild_only_tests` will be set to an empty list anyway,
which means the `meson-test-prereq` target is executed, which contains
the targets for all tests.

Instead, `rebuild_only_tests` should only be set to an empty list,
when the selected tests are identical to the complete list of available
tests: `tests == self.tests`

Since after this commit we compare directly to the result of `self.get_tests()`, this
will do the correct thing for all other options, which change or filter
the list of selected tests (e.g. `self.options.args`, `self.options.slice`).

Author: maj0e

mesonbuild/mtest.py

@@ -1891,7 +1891,12 @@ def doit(self) -> int:
             raise RuntimeError('Test harness object can only be used once.')
         self.is_run = True
         tests = self.get_tests()
-        rebuild_only_tests = tests if self.options.args else []
+        # NOTE: If all tests are selected anyway, we pass
+        # an empty list to `rebuild_deps`, which then will execute
+        # the "meson-test-prereq" ninja target as a fallback.
+        # This prevents situations, where ARG_MAX may overflow
+        # if there are many targets.
+        rebuild_only_tests = tests if tests != self.tests else []
         if not tests:
             return 0
         if not self.options.no_rebuild and not rebuild_deps(self.ninja, self.options.wd, rebuild_only_tests, self.options.benchmark):