PkgConfigDependency: Don't try to resolve internal compiler libs

-lc -lm -ldl -lrt -lpthread are special linker arguments that should
never be resolved to on-disk libraries.

Closes https://github.com/mesonbuild/meson/issues/3879

mesonbuild/compilers/c.py

@@ -47,11 +47,14 @@ from .compilers import (
     RunResult,
 )
 
+gnu_compiler_internal_libs = ('m', 'c', 'pthread', 'dl', 'rt')
+
 
 class CCompiler(Compiler):
     library_dirs_cache = {}
     program_dirs_cache = {}
     find_library_cache = {}
+    internal_libs = gnu_compiler_internal_libs
 
     def __init__(self, exelist, version, is_cross, exe_wrapper=None, **kwargs):
         # If a child ObjC or CPP class has already set it, don't set it ourselves
@@ -905,10 +908,13 @@ class CCompiler(Compiler):
         # First try if we can just add the library as -l.
         # Gcc + co seem to prefer builtin lib dirs to -L dirs.
         # Only try to find std libs if no extra dirs specified.
-        if not extra_dirs:
+        if not extra_dirs or libname in self.internal_libs:
             args = ['-l' + libname]
             if self.links(code, env, extra_args=args):
                 return args
+            # Don't do a manual search for internal libs
+            if libname in self.internal_libs:
+                return None
         # Not found or we want to use a specific libtype? Try to find the
         # library file itself.
         patterns = self.get_library_naming(env, libtype)
@@ -1188,7 +1194,8 @@ class IntelCCompiler(IntelCompiler, CCompiler):
 class VisualStudioCCompiler(CCompiler):
     std_warn_args = ['/W3']
     std_opt_args = ['/O2']
-    ignore_libs = ('m', 'c', 'pthread')
+    ignore_libs = gnu_compiler_internal_libs
+    internal_libs = ()
 
     def __init__(self, exelist, version, is_cross, exe_wrap, is_64):
         CCompiler.__init__(self, exelist, version, is_cross, exe_wrap)

mesonbuild/compilers/compilers.py

@@ -661,6 +661,9 @@ class Compiler:
     # Libraries to ignore in find_library() since they are provided by the
     # compiler or the C library. Currently only used for MSVC.
     ignore_libs = ()
+    # Libraries that are internal compiler implementations, and must not be
+    # manually searched.
+    internal_libs = ()
     # Cache for the result of compiler checks which can be cached
     compiler_check_cache = {}
 

mesonbuild/dependencies/base.py

@@ -623,12 +623,16 @@ class PkgConfigDependency(ExternalDependency):
                 # arguments as-is and then adding the libpaths at the end.
                 else:
                     args = None
-                if args:
+                if args is not None:
                     libs_found.add(lib)
                     # Replace -l arg with full path to library if available
-                    # else, library is provided by the compiler and can't be resolved
-                    if not args[0].startswith('-l'):
-                        lib = args[0]
+                    # else, library is either to be ignored, or is provided by
+                    # the compiler, can't be resolved, and should be used as-is
+                    if args:
+                        if not args[0].startswith('-l'):
+                            lib = args[0]
+                    else:
+                        continue
                 else:
                     # Library wasn't found, maybe we're looking in the wrong
                     # places or the library will be provided with LDFLAGS or

run_unittests.py

@@ -51,11 +51,15 @@ from run_tests import get_builddir_target_args, get_backend_commands, Backend
 from run_tests import ensure_backend_detects_changes, run_configure_inprocess
 from run_tests import run_mtest_inprocess
 
-# Fake class for mocking
+# Fake classes for mocking
 class FakeBuild:
     def __init__(self, env):
         self.environment = env
 
+class FakeCompilerOptions:
+    def __init__(self):
+        self.value = []
+
 def get_dynamic_section_entry(fname, entry):
     if is_cygwin() or is_osx():
             raise unittest.SkipTest('Test only applicable to ELF platforms')
@@ -605,6 +609,7 @@ class InternalTests(unittest.TestCase):
             env = Environment('', '', get_fake_options(''))
             compiler = env.detect_c_compiler(False)
             env.coredata.compilers = {'c': compiler}
+            env.coredata.compiler_options['c_link_args'] = FakeCompilerOptions()
             p1 = Path(tmpdir) / '1'
             p2 = Path(tmpdir) / '2'
             p1.mkdir()
@@ -614,6 +619,12 @@ class InternalTests(unittest.TestCase):
             # libbar.a is in both prefixes
             (p1 / 'libbar.a').open('w').close()
             (p2 / 'libbar.a').open('w').close()
+            # 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()
 
             def fake_call_pkgbin(self, args, env=None):
                 if '--libs' not in args:
@@ -622,6 +633,8 @@ class InternalTests(unittest.TestCase):
                     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())
+                if args[0] == 'internal':
+                    return 0, '-L{} -lpthread -lm -lc -lrt -ldl'.format(p1.as_posix())
 
             old_call = PkgConfigDependency._call_pkgbin
             old_check = PkgConfigDependency.check_pkgconfig
@@ -634,6 +647,14 @@ class InternalTests(unittest.TestCase):
                              [(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_id() == '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
@@ -2797,7 +2818,7 @@ class WindowsTests(BasePlatformTests):
         if cc.id != 'msvc':
             raise unittest.SkipTest('Not using MSVC')
         # To force people to update this test, and also test
-        self.assertEqual(set(cc.ignore_libs), {'c', 'm', 'pthread'})
+        self.assertEqual(set(cc.ignore_libs), {'c', 'm', 'pthread', 'dl', 'rt'})
         for l in cc.ignore_libs:
             self.assertEqual(cc.find_library(l, env, []), [])