depfixer: don't invoke install_name_tool on non-darwin targets

fix_rpath() fell through to the install_name_tool/otool path whenever
a file wasn't valid ELF, regardless of target system.

detect_elf_type() exits 0 for any non-ELF file, and that exit was caught and treated as "try darwin fixup" unconditionally.

On a non-darwin system with install_name_tool on PATH
(e.g. darwin cross-toolchain installed alongside), this ran otool/install_name_tool against native binaries.

Gate the darwin-only path on system == 'darwin'.

Fixes #8027

Author: harshverma27

mesonbuild/scripts/depfixer.py

@@ -832,6 +832,9 @@ def fix_rpath(fname: str, rpath_dirs_to_remove: T.Set[bytes], new_rpath: T.Union
             pass
         else:
             raise
+    # Non-ELF files fall through here on any system, not just darwin (#8027)
+    if system != 'darwin':
+        return
     # We don't look for this on import because it will do a useless PATH lookup
     # on non-mac platforms. That can be expensive on some Windows machines
     # (up to 30ms), which is significant with --only-changed. For details, see:

unittests/internaltests.py

@@ -25,6 +25,7 @@
 import mesonbuild.envconfig
 import mesonbuild.environment
 import mesonbuild.modules.gnome
+import mesonbuild.scripts.depfixer
 import mesonbuild.scripts.env2mfile
 from mesonbuild import coredata
 from mesonbuild.compilers.c import ClangCCompiler, GnuCCompiler
@@ -2233,3 +2234,13 @@ def expected_binaries(gnu_tuple: str) -> T.Dict[str, T.List[str]]:
                 self.assertEqual(actual.compile_args, expected.compile_args)
                 self.assertEqual(actual.link_args, expected.link_args)
                 self.assertEqual(actual.cmake, expected.cmake)
+
+    def test_depfixer_skips_install_name_tool_on_non_darwin(self) -> None:
+        # non-ELF file on non-darwin must not probe for install_name_tool (#8027)
+        with tempfile.NamedTemporaryFile(suffix='.so') as f:
+            f.write(b'not an elf file')
+            f.flush()
+            with mock.patch('mesonbuild.scripts.depfixer.shutil.which') as mock_which:
+                mesonbuild.scripts.depfixer.fix_rpath(
+                    f.name, set(), '', '', {}, system='linux', verbose=False)
+                mock_which.assert_not_called()