find_library: Check arch of libraries on Darwin

macOS provides the tool `lipo` to check the archs supported by an
object (executable, static library, dylib, etc). This is especially
useful for fat archives, but it also helps with thin archives.

Without this, the linker will fail to link to the library we mistakenly
'found' like so:

ld: warning: ignoring file /path/to/libfoo.a, missing required architecture armv7 in file /path/to/libfoo.a

1 files changed, 42 insertions, 30 deletions

diff --git a/run_unittests.py b/run_unittests.py
index b8b3192..72ab062 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -45,7 +45,7 @@ from mesonbuild.interpreter import Interpreter, ObjectHolder
 from mesonbuild.mesonlib import (
     is_windows, is_osx, is_cygwin, is_dragonflybsd, is_openbsd, is_haiku,
     windows_proof_rmtree, python_command, version_compare,
-    BuildDirLock, Version
+    BuildDirLock, Version, PerMachine
 )
 from mesonbuild.environment import detect_ninja
 from mesonbuild.mesonlib import MesonException, EnvironmentException
@@ -781,6 +781,17 @@ class InternalTests(unittest.TestCase):
 
         https://github.com/mesonbuild/meson/issues/3951
         '''
+        def create_static_lib(name):
+            if not is_osx():
+                name.open('w').close()
+                return
+            src = name.with_suffix('.c')
+            out = name.with_suffix('.o')
+            with src.open('w') as f:
+                f.write('int meson_foobar (void) { return 0; }')
+            subprocess.check_call(['clang', '-c', str(src), '-o', str(out)])
+            subprocess.check_call(['ar', 'csr', str(name), str(out)])
+
         with tempfile.TemporaryDirectory() as tmpdir:
             pkgbin = ExternalProgram('pkg-config', command=['pkg-config'], silent=True)
             env = get_fake_env()
@@ -792,16 +803,16 @@ class InternalTests(unittest.TestCase):
             p1.mkdir()
             p2.mkdir()
             # libfoo.a is in one prefix
-            (p1 / 'libfoo.a').open('w').close()
+            create_static_lib(p1 / 'libfoo.a')
             # libbar.a is in both prefixes
-            (p1 / 'libbar.a').open('w').close()
-            (p2 / 'libbar.a').open('w').close()
+            create_static_lib(p1 / 'libbar.a')
+            create_static_lib(p2 / 'libbar.a')
             # Ensure that we never statically link to these
-            (p1 / 'libpthread.a').open('w').close()
-            (p1 / 'libm.a').open('w').close()
-            (p1 / 'libc.a').open('w').close()
-            (p1 / 'libdl.a').open('w').close()
-            (p1 / 'librt.a').open('w').close()
+            create_static_lib(p1 / 'libpthread.a')
+            create_static_lib(p1 / 'libm.a')
+            create_static_lib(p1 / 'libc.a')
+            create_static_lib(p1 / 'libdl.a')
+            create_static_lib(p1 / 'librt.a')
 
             def fake_call_pkgbin(self, args, env=None):
                 if '--libs' not in args:
@@ -815,30 +826,31 @@ class InternalTests(unittest.TestCase):
 
             old_call = PkgConfigDependency._call_pkgbin
             old_check = PkgConfigDependency.check_pkgconfig
-            old_pkgbin = PkgConfigDependency.class_pkgbin
             PkgConfigDependency._call_pkgbin = fake_call_pkgbin
             PkgConfigDependency.check_pkgconfig = lambda x, _: pkgbin
             # Test begins
-            kwargs = {'required': True, 'silent': True}
-            foo_dep = PkgConfigDependency('foo', env, kwargs)
-            self.assertEqual(foo_dep.get_link_args(),
-                             [(p1 / 'libfoo.a').as_posix(), (p2 / 'libbar.a').as_posix()])
-            bar_dep = PkgConfigDependency('bar', env, kwargs)
-            self.assertEqual(bar_dep.get_link_args(), [(p2 / 'libbar.a').as_posix()])
-            internal_dep = PkgConfigDependency('internal', env, kwargs)
-            if compiler.get_argument_syntax() == 'msvc':
-                self.assertEqual(internal_dep.get_link_args(), [])
-            else:
-                link_args = internal_dep.get_link_args()
-                for link_arg in link_args:
-                    for lib in ('pthread', 'm', 'c', 'dl', 'rt'):
-                        self.assertNotIn('lib{}.a'.format(lib), link_arg, msg=link_args)
-            # Test ends
-            PkgConfigDependency._call_pkgbin = old_call
-            PkgConfigDependency.check_pkgconfig = old_check
-            # Reset dependency class to ensure that in-process configure doesn't mess up
-            PkgConfigDependency.pkgbin_cache = {}
-            PkgConfigDependency.class_pkgbin = old_pkgbin
+            try:
+                kwargs = {'required': True, 'silent': True}
+                foo_dep = PkgConfigDependency('foo', env, kwargs)
+                self.assertEqual(foo_dep.get_link_args(),
+                                 [(p1 / 'libfoo.a').as_posix(), (p2 / 'libbar.a').as_posix()])
+                bar_dep = PkgConfigDependency('bar', env, kwargs)
+                self.assertEqual(bar_dep.get_link_args(), [(p2 / 'libbar.a').as_posix()])
+                internal_dep = PkgConfigDependency('internal', env, kwargs)
+                if compiler.get_argument_syntax() == 'msvc':
+                    self.assertEqual(internal_dep.get_link_args(), [])
+                else:
+                    link_args = internal_dep.get_link_args()
+                    for link_arg in link_args:
+                        for lib in ('pthread', 'm', 'c', 'dl', 'rt'):
+                            self.assertNotIn('lib{}.a'.format(lib), link_arg, msg=link_args)
+            finally:
+                # Test ends
+                PkgConfigDependency._call_pkgbin = old_call
+                PkgConfigDependency.check_pkgconfig = old_check
+                # Reset dependency class to ensure that in-process configure doesn't mess up
+                PkgConfigDependency.pkgbin_cache = {}
+                PkgConfigDependency.class_pkgbin = PerMachine(None, None, None)
 
     def test_version_compare(self):
         comparefunc = mesonbuild.mesonlib.version_compare_many