dependencies: Add function to strip system -L paths

PkgConfig automatically removes -L paths from libdirs if the -L points
to a system path. It knows what these paths are by taking this as a
configure option at build time, which the distro maintainers set
appropriately and everything works. This allows one to have two
versions of a package installed, a system and non system, and then
override PKG_CONFIG_PATH to use the non system version, and everything
just works. For non-pkgconfig dependencies (such as LLVM) meson needs to
strip these themselves to avoid breaking the above use case.

2 files changed, 29 insertions, 0 deletions

diff --git a/mesonbuild/dependencies/base.py b/mesonbuild/dependencies/base.py
index 0d9742d..9913a0b 100644
--- a/mesonbuild/dependencies/base.py
+++ b/mesonbuild/dependencies/base.py
@@ -640,3 +640,14 @@ def find_external_dependency(name, env, kwargs):
         raise pkg_exc
     mlog.log('Dependency', mlog.bold(name), 'found:', mlog.red('NO'))
     return pkgdep
+
+
+def strip_system_libdirs(environment, link_args):
+    """Remove -L<system path> arguments.
+
+    leaving these in will break builds where a user has a version of a library
+    in the system path, and a different version not in the system path if they
+    want to link against the non-system path version.
+    """
+    exclude = {'-L{}'.format(p) for p in environment.get_compiler_system_dirs()}
+    return [l for l in link_args if l not in exclude]
diff --git a/mesonbuild/environment.py b/mesonbuild/environment.py
index 2f33a03..a746cab 100644
--- a/mesonbuild/environment.py
+++ b/mesonbuild/environment.py
@@ -887,6 +887,24 @@ class Environment:
     def get_datadir(self):
         return self.coredata.get_builtin_option('datadir')
 
+    def get_compiler_system_dirs(self):
+        for comp in self.coredata.compilers.values():
+            if isinstance(comp, compilers.ClangCompiler):
+                index = 1
+                break
+            elif isinstance(comp, compilers.GnuCompiler):
+                index = 2
+                break
+        else:
+            # This option is only supported by gcc and clang. If we don't get a
+            # GCC or Clang compiler return and empty list.
+            return []
+
+        p, out, _ = Popen_safe(comp.get_exelist() + ['-print-search-dirs'])
+        if p.returncode != 0:
+            raise mesonlib.MesonException('Could not calculate system search dirs')
+        out = out.split('\n')[index].lstrip('libraries: =').split(':')
+        return [os.path.normpath(p) for p in out]
 
 def get_args_from_envvars(compiler):
     """