PkgConfigDependency: Fix library path search order

We were searching the library paths in the reverse order, which meant
that we'd pick libraries from the wrong prefix.

Closes https://github.com/mesonbuild/meson/issues/3951

4 files changed, 77 insertions, 28 deletions

diff --git a/mesonbuild/compilers/c.py b/mesonbuild/compilers/c.py
index dbbbed2..47cb568 100644
--- a/mesonbuild/compilers/c.py
+++ b/mesonbuild/compilers/c.py
@@ -16,6 +16,7 @@ import re
 import glob
 import os.path
 import subprocess
+from pathlib import Path
 
 from .. import mlog
 from .. import coredata
@@ -883,13 +884,13 @@ class CCompiler(Compiler):
 
     @classmethod
     def _get_trials_from_pattern(cls, pattern, directory, libname):
-        f = os.path.join(directory, pattern.format(libname))
+        f = Path(directory) / pattern.format(libname)
         # Globbing for OpenBSD
         if '*' in pattern:
             # NOTE: globbing matches directories and broken symlinks
             # so we have to do an isfile test on it later
-            return cls._sort_shlibs_openbsd(glob.glob(f))
-        return [f]
+            return cls._sort_shlibs_openbsd(glob.glob(str(f)))
+        return [f.as_posix()]
 
     @staticmethod
     def _get_file_from_list(files):
diff --git a/mesonbuild/dependencies/base.py b/mesonbuild/dependencies/base.py
index 63b817a..f087db6 100644
--- a/mesonbuild/dependencies/base.py
+++ b/mesonbuild/dependencies/base.py
@@ -584,26 +584,7 @@ class PkgConfigDependency(ExternalDependency):
                                       (self.name, out))
         self.compile_args = self._convert_mingw_paths(shlex.split(out))
 
-    def _set_libs(self):
-        env = None
-        libcmd = [self.name, '--libs']
-        if self.static:
-            libcmd.append('--static')
-        # Force pkg-config to output -L fields even if they are system
-        # paths so we can do manual searching with cc.find_library() later.
-        env = os.environ.copy()
-        env['PKG_CONFIG_ALLOW_SYSTEM_LIBS'] = '1'
-        ret, out = self._call_pkgbin(libcmd, env=env)
-        if ret != 0:
-            raise DependencyException('Could not generate libs for %s:\n\n%s' %
-                                      (self.name, out))
-        # Also get the 'raw' output without -Lfoo system paths for usage when
-        # a library can't be found, and also in gnome.generate_gir
-        # + gnome.gtkdoc which need -L -l arguments.
-        ret, out_raw = self._call_pkgbin(libcmd)
-        if ret != 0:
-            raise DependencyException('Could not generate libs for %s:\n\n%s' %
-                                      (self.name, out_raw))
+    def _search_libs(self, out, out_raw):
         link_args = []
         raw_link_args = []
         # Library paths should be safe to de-dup
@@ -634,7 +615,7 @@ class PkgConfigDependency(ExternalDependency):
                     continue
                 if self.clib_compiler:
                     args = self.clib_compiler.find_library(lib[2:], self.env,
-                                                           list(libpaths), libtype)
+                                                           list(reversed(libpaths)), libtype)
                 # If the project only uses a non-clib language such as D, Rust,
                 # C#, Python, etc, all we can do is limp along by adding the
                 # arguments as-is and then adding the libpaths at the end.
@@ -679,14 +660,34 @@ class PkgConfigDependency(ExternalDependency):
             if lib.startswith('-L') and not lib.startswith(('-L-l', '-L-L')):
                 raw_libpaths.add(lib[2:])
             raw_link_args.append(lib)
-        # Set everything
-        self.link_args = link_args
-        self.raw_link_args = raw_link_args
         # Add all -Lbar args if we have -lfoo args in link_args
         if libs_notfound:
             # Order of -L flags doesn't matter with ld, but it might with other
             # linkers such as MSVC, so prepend them.
-            self.link_args = ['-L' + lp for lp in raw_libpaths] + self.link_args
+            link_args = ['-L' + lp for lp in raw_libpaths] + link_args
+        return link_args, raw_link_args
+
+    def _set_libs(self):
+        env = None
+        libcmd = [self.name, '--libs']
+        if self.static:
+            libcmd.append('--static')
+        # Force pkg-config to output -L fields even if they are system
+        # paths so we can do manual searching with cc.find_library() later.
+        env = os.environ.copy()
+        env['PKG_CONFIG_ALLOW_SYSTEM_LIBS'] = '1'
+        ret, out = self._call_pkgbin(libcmd, env=env)
+        if ret != 0:
+            raise DependencyException('Could not generate libs for %s:\n\n%s' %
+                                      (self.name, out))
+        # Also get the 'raw' output without -Lfoo system paths for adding -L
+        # args with -lfoo when a library can't be found, and also in
+        # gnome.generate_gir + gnome.gtkdoc which need -L -l arguments.
+        ret, out_raw = self._call_pkgbin(libcmd)
+        if ret != 0:
+            raise DependencyException('Could not generate libs for %s:\n\n%s' %
+                                      (self.name, out_raw))
+        self.link_args, self.raw_link_args = self._search_libs(out, out_raw)
 
     def get_pkgconfig_variable(self, variable_name, kwargs):
         options = ['--variable=' + variable_name, self.name]
diff --git a/mesonbuild/mesonlib.py b/mesonbuild/mesonlib.py
index ab03e00..de85ae6 100644
--- a/mesonbuild/mesonlib.py
+++ b/mesonbuild/mesonlib.py
@@ -1094,6 +1094,9 @@ class OrderedSet(collections.MutableSet):
                 '", "'.join(repr(e) for e in self.__container.keys()))
         return 'OrderedSet()'
 
+    def __reversed__(self):
+        return reversed(self.__container)
+
     def add(self, value):
         self.__container[value] = None
 
diff --git a/run_unittests.py b/run_unittests.py
index 806390c..7c8c595 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -601,6 +601,50 @@ class InternalTests(unittest.TestCase):
                              'mesonbuild.compilers.c.for_windows', true):
                 self._test_all_naming(cc, env, patterns, 'windows-msvc')
 
+    def test_pkgconfig_parse_libs(self):
+        '''
+        Unit test for parsing of pkg-config output to search for libraries
+
+        https://github.com/mesonbuild/meson/issues/3951
+        '''
+        with tempfile.TemporaryDirectory() as tmpdir:
+            pkgbin = ExternalProgram('pkg-config', command=['pkg-config'], silent=True)
+            env = Environment('', '', get_fake_options(''))
+            compiler = env.detect_c_compiler(False)
+            env.coredata.compilers = {'c': compiler}
+            p1 = Path(tmpdir) / '1'
+            p2 = Path(tmpdir) / '2'
+            p1.mkdir()
+            p2.mkdir()
+            # libfoo.a is in one prefix
+            (p1 / 'libfoo.a').open('w').close()
+            # libbar.a is in both prefixes
+            (p1 / 'libbar.a').open('w').close()
+            (p2 / 'libbar.a').open('w').close()
+
+            def fake_call_pkgbin(self, args, env=None):
+                if '--libs' not in args:
+                    return 0, ''
+                if args[0] == 'foo':
+                    return 0, '-L{} -lfoo -L{} -lbar'.format(p1.as_posix(), p2.as_posix())
+                if args[0] == 'bar':
+                    return 0, '-L{} -lbar'.format(p2.as_posix())
+
+            old_call = PkgConfigDependency._call_pkgbin
+            old_check = PkgConfigDependency.check_pkgconfig
+            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()])
+            # Test ends
+            PkgConfigDependency._call_pkgbin = old_call
+            PkgConfigDependency.check_pkgconfig = old_check
+
 
 class BasePlatformTests(unittest.TestCase):
     def setUp(self):