Improve generation of pkg-config files for static only libraries.

Previously pkg-config files generated by the pkgconfig modules for static libraries
with dependencies could only be used in a dependencies with `static: true`.

This was caused by the dependencies only appearing in Libs.private even
if they are needed in the default linking mode. But a user of a
dependency should not have to know if the default linking mode is static
or dynamic; A dependency('somelib') call should always pull in all
needed pieces into the build.

Now for meson build static libraries passed via `libraries` to the generate
method automatically promote dependencies to public.

9 files changed, 74 insertions, 3 deletions

diff --git a/docs/markdown/snippets/pkg-config-fix-static-only.md b/docs/markdown/snippets/pkg-config-fix-static-only.md
new file mode 100644
index 0000000..31cd389
--- /dev/null
+++ b/docs/markdown/snippets/pkg-config-fix-static-only.md
@@ -0,0 +1,12 @@
+## Improved generation of pkg-config files for static only libraries.
+
+Previously pkg-config files generated by the pkgconfig modules for static libraries
+with dependencies could only be used in a dependencies with `static: true`.
+
+Now the generated file contains the needed dependencies libraries directly within
+`Requires` and `Libs` for build static libraries passed via the `libraries` keyword
+argument.
+
+Projects that install both a static and a shared version of a library should use
+the result of `both_libraries` to the pkg config file generator or use
+configure_file for more complicated setups.
diff --git a/mesonbuild/modules/pkgconfig.py b/mesonbuild/modules/pkgconfig.py
index 6a7e962..6f0e717 100644
--- a/mesonbuild/modules/pkgconfig.py
+++ b/mesonbuild/modules/pkgconfig.py
@@ -119,11 +119,15 @@ class DependenciesHelper:
                         obj.generated_pc = self.name
             elif isinstance(obj, (build.SharedLibrary, build.StaticLibrary)):
                 processed_libs.append(obj)
-                self.add_priv_libs(obj.get_dependencies())
-                self.add_priv_libs(obj.get_external_deps())
                 if public:
                     if not hasattr(obj, 'generated_pc'):
                         obj.generated_pc = self.name
+                if isinstance(obj, build.StaticLibrary) and public:
+                    self.add_pub_libs(obj.get_dependencies())
+                    self.add_pub_libs(obj.get_external_deps())
+                else:
+                    self.add_priv_libs(obj.get_dependencies())
+                    self.add_priv_libs(obj.get_external_deps())
             elif isinstance(obj, str):
                 processed_libs.append(obj)
             else:
diff --git a/run_unittests.py b/run_unittests.py
index 1e8a778..0f9a50b 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -2841,6 +2841,27 @@ endian = 'little'
             self.assertTrue(os.path.isfile(test_exe))
             subprocess.check_call(test_exe, env=myenv)
 
+    @unittest.skipIf(shutil.which('pkg-config') is None, 'Pkg-config not found.')
+    def test_pkgconfig_internal_libraries(self):
+        '''
+        '''
+        with tempfile.TemporaryDirectory() as tempdirname:
+            # build library
+            testdirbase = os.path.join(self.unit_test_dir, '28 pkgconfig use libraries')
+            testdirlib = os.path.join(testdirbase, 'lib')
+            self.init(testdirlib, extra_args=['--prefix=' + tempdirname,
+                                              '--libdir=lib',
+                                              '--default-library=static'], default_args=False)
+            self.build()
+            self.install(use_destdir=False)
+
+            # build user of library
+            pkg_dir = os.path.join(tempdirname, 'lib/pkgconfig')
+            os.environ['PKG_CONFIG_PATH'] = pkg_dir
+            self.new_builddir()
+            self.init(os.path.join(testdirbase, 'app'))
+            self.build()
+
 
 class LinuxArmCrossCompileTests(BasePlatformTests):
     '''
diff --git a/test cases/common/51 pkgconfig-gen/dependencies/meson.build b/test cases/common/51 pkgconfig-gen/dependencies/meson.build
index 640115a..047e7e7 100644
--- a/test cases/common/51 pkgconfig-gen/dependencies/meson.build
+++ b/test cases/common/51 pkgconfig-gen/dependencies/meson.build
@@ -5,7 +5,7 @@ pkgg = import('pkgconfig')
 # libmain internally use libinternal and expose libexpose in its API
 exposed_lib = shared_library('libexposed', 'exposed.c')
 internal_lib = shared_library('libinternal', 'internal.c')
-main_lib = static_library('libmain', link_with : [exposed_lib, internal_lib])
+main_lib = both_libraries('libmain', link_with : [exposed_lib, internal_lib])
 
 pkgg.generate(exposed_lib)
 
diff --git a/test cases/unit/28 pkgconfig use libraries/app/app.c b/test cases/unit/28 pkgconfig use libraries/app/app.c
new file mode 100644
index 0000000..b271a9e
--- /dev/null
+++ b/test cases/unit/28 pkgconfig use libraries/app/app.c
@@ -0,0 +1,6 @@
+void libb_func();
+
+int main() {
+    libb_func();
+    return 0;
+}
diff --git a/test cases/unit/28 pkgconfig use libraries/app/meson.build b/test cases/unit/28 pkgconfig use libraries/app/meson.build
new file mode 100644
index 0000000..3d85a32
--- /dev/null
+++ b/test cases/unit/28 pkgconfig use libraries/app/meson.build
@@ -0,0 +1,5 @@
+project('app', ['c'])
+
+b = dependency('test-b')
+
+executable('app', 'app.c', dependencies : [b])
diff --git a/test cases/unit/28 pkgconfig use libraries/lib/liba.c b/test cases/unit/28 pkgconfig use libraries/lib/liba.c
new file mode 100644
index 0000000..e98906b
--- /dev/null
+++ b/test cases/unit/28 pkgconfig use libraries/lib/liba.c
@@ -0,0 +1,2 @@
+void liba_func() {
+}
diff --git a/test cases/unit/28 pkgconfig use libraries/lib/libb.c b/test cases/unit/28 pkgconfig use libraries/lib/libb.c
new file mode 100644
index 0000000..3160e5f
--- /dev/null
+++ b/test cases/unit/28 pkgconfig use libraries/lib/libb.c
@@ -0,0 +1,5 @@
+void liba_func();
+
+void libb_func() {
+    liba_func();
+}
diff --git a/test cases/unit/28 pkgconfig use libraries/lib/meson.build b/test cases/unit/28 pkgconfig use libraries/lib/meson.build
new file mode 100644
index 0000000..748adf4
--- /dev/null
+++ b/test cases/unit/28 pkgconfig use libraries/lib/meson.build
@@ -0,0 +1,16 @@
+project('lib', ['c'])
+
+a = library('test-a', 'liba.c', install: true)
+
+b = library('test-b', 'libb.c', link_with: a, install: true)
+
+import('pkgconfig').generate(
+    version: '0.0',
+    description: 'test library',
+    filebase: 'test-b',
+    name: 'test library',
+    libraries: [b],
+    subdirs: ['.']
+)
+
+