Do not leak out private dependencies for shared libraries.

mesonbuild/modules/pkgconfig.py

@@ -93,7 +93,17 @@ class DependenciesHelper:
                 if obj.found():
                     processed_libs += obj.get_link_args()
                     processed_cflags += obj.get_compile_args()
-            elif isinstance(obj, (build.SharedLibrary, build.StaticLibrary)):
+            elif isinstance(obj, build.SharedLibrary):
+                processed_libs.append(obj)
+            elif isinstance(obj, build.StaticLibrary):
+                # Due to a "feature" in pkgconfig, it leaks out private dependencies.
+                # Thus we will not add them to the pc file unless the target
+                # we are processing is a static library.
+                #
+                # This way (hopefully) "pkgconfig --libs --static foobar" works
+                # and "pkgconfig --cflags/--libs foobar" does not have any trace
+                # of dependencies that the build file creator has not explicitly
+                # added to the dependency list.
                 processed_libs.append(obj)
                 if public:
                     if not hasattr(obj, 'generated_pc'):

run_unittests.py

@@ -2726,6 +2726,13 @@ endian = 'little'
             self.assertTrue(os.path.exists(os.path.join(pkg_dir, 'libpkgdep.pc')))
             lib_dir = os.path.join(tempdirname, 'lib')
             os.environ['PKG_CONFIG_PATH'] = pkg_dir
+            # Private internal libraries must not leak out.
+            pkg_out = subprocess.check_output(['pkg-config', '--static', '--libs', 'libpkgdep'])
+            self.assertFalse(b'libpkgdep-int' in pkg_out, 'Internal library leaked out.')
+            # Dependencies must not leak to cflags when building only a shared library.
+            pkg_out = subprocess.check_output(['pkg-config', '--cflags', 'libpkgdep'])
+            self.assertFalse(b'glib' in pkg_out, 'Internal dependency leaked to headers.')
+            # Test that the result is usable.
             self.init(testdir2)
             self.build()
             myenv = os.environ.copy()