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

5 files changed, 85 insertions, 39 deletions

diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index 493fc0d..9b215b2 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -2347,15 +2347,14 @@ rule FORTRAN_DEP_HACK%s
         target_args = self.build_target_link_arguments(linker, target.link_whole_targets)
         return linker.get_link_whole_for(target_args) if len(target_args) else []
 
-    @staticmethod
     @lru_cache(maxsize=None)
-    def guess_library_absolute_path(linker, libname, search_dirs, patterns):
+    def guess_library_absolute_path(self, linker, libname, search_dirs, patterns):
         for d in search_dirs:
             for p in patterns:
                 trial = CCompiler._get_trials_from_pattern(p, d, libname)
                 if not trial:
                     continue
-                trial = CCompiler._get_file_from_list(trial)
+                trial = CCompiler._get_file_from_list(self.environment, trial)
                 if not trial:
                     continue
                 # Return the first result
diff --git a/mesonbuild/compilers/c.py b/mesonbuild/compilers/c.py
index 0a90c8c..a591183 100644
--- a/mesonbuild/compilers/c.py
+++ b/mesonbuild/compilers/c.py
@@ -27,6 +27,7 @@ from . import compilers
 from ..mesonlib import (
     EnvironmentException, MesonException, version_compare, Popen_safe, listify,
     for_windows, for_darwin, for_cygwin, for_haiku, for_openbsd,
+    darwin_get_object_archs
 )
 from .c_function_attributes import C_FUNC_ATTRIBUTES
 
@@ -980,10 +981,28 @@ class CCompiler(Compiler):
         return [f.as_posix()]
 
     @staticmethod
-    def _get_file_from_list(files: List[str]) -> str:
+    def _get_file_from_list(env, files: List[str]) -> str:
+        '''
+        We just check whether the library exists. We can't do a link check
+        because the library might have unresolved symbols that require other
+        libraries. On macOS we check if the library matches our target
+        architecture.
+        '''
+        # If not building on macOS for Darwin, do a simple file check
+        if not env.machines.host.is_darwin() or not env.machines.build.is_darwin():
+            for f in files:
+                if os.path.isfile(f):
+                    return f
+        # Run `lipo` and check if the library supports the arch we want
         for f in files:
-            if os.path.isfile(f):
+            if not os.path.isfile(f):
+                continue
+            archs = darwin_get_object_archs(f)
+            if archs and env.machines.host.cpu_family in archs:
                 return f
+            else:
+                mlog.debug('Rejected {}, supports {} but need {}'
+                           .format(f, archs, env.machines.host.cpu_family))
         return None
 
     @functools.lru_cache()
@@ -1024,10 +1043,7 @@ class CCompiler(Compiler):
                 trial = self._get_trials_from_pattern(p, d, libname)
                 if not trial:
                     continue
-                # We just check whether the library exists. We can't do a link
-                # check because the library might have unresolved symbols that
-                # require other libraries.
-                trial = self._get_file_from_list(trial)
+                trial = self._get_file_from_list(env, trial)
                 if not trial:
                     continue
                 return [trial]
diff --git a/mesonbuild/mesonlib.py b/mesonbuild/mesonlib.py
index 5529ce4..09228dc 100644
--- a/mesonbuild/mesonlib.py
+++ b/mesonbuild/mesonlib.py
@@ -461,6 +461,24 @@ def exe_exists(arglist):
         pass
     return False
 
+lru_cache(maxsize=None)
+def darwin_get_object_archs(objpath):
+    '''
+    For a specific object (executable, static library, dylib, etc), run `lipo`
+    to fetch the list of archs supported by it. Supports both thin objects and
+    'fat' objects.
+    '''
+    _, stdo, stderr = Popen_safe(['lipo', '-archs', objpath])
+    if not stdo:
+        mlog.debug('lipo {}: {}'.format(objpath, stderr))
+        return None
+    # Convert from lipo-style archs to meson-style CPUs
+    stdo = stdo.replace('i386', 'x86')
+    # Add generic name for armv7 and armv7s
+    if 'armv7' in stdo:
+        stdo += ' arm'
+    return stdo.split()
+
 def detect_vcs(source_dir):
     vcs_systems = [
         dict(name = 'git',        cmd = 'git', repo_dir = '.git', get_rev = 'git describe --dirty=+', rev_regex = '(.*)', dep = '.git/logs/HEAD'),
diff --git a/run_tests.py b/run_tests.py
index 943e16f..20cb4e2 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -81,6 +81,7 @@ def get_fake_env(sdir='', bdir=None, prefix='', opts=None):
         opts = get_fake_options(prefix)
     env = Environment(sdir, bdir, opts)
     env.coredata.compiler_options['c_args'] = FakeCompilerOptions()
+    env.machines.host.cpu_family = 'x86_64' # Used on macOS inside find_library
     return env
 
 
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