Introduce dataonly for the pkgconfig module

This allows users to disable writing out the inbuilt variables to
the pkg-config file as they might actualy not be required.

One reason to have this is for architecture-independent pkg-config
files in projects which also have architecture-dependent outputs.

For example : https://gitlab.freedesktop.org/wayland/weston/issues/269

Fixes #4011

6 files changed, 68 insertions, 22 deletions

diff --git a/docs/markdown/Pkgconfig-module.md b/docs/markdown/Pkgconfig-module.md
index 678090b..13fc4e6 100644
--- a/docs/markdown/Pkgconfig-module.md
+++ b/docs/markdown/Pkgconfig-module.md
@@ -56,6 +56,8 @@ keyword arguments.
    D sources referred to by this pkg-config file
 - `uninstalled_variables` used instead of the `variables` keyword argument, when
   generating the uninstalled pkg-config file. Since *0.54.0*
+- `dataonly` field. (*since 0.54.0*) this is used for architecture-independent
+   pkg-config files in projects which also have architecture-dependent outputs.
 
 Since 0.46 a `StaticLibrary` or `SharedLibrary` object can optionally be passed
 as first positional argument. If one is provided a default value will be
diff --git a/docs/markdown/snippets/pkgconfig_dataonly.md b/docs/markdown/snippets/pkgconfig_dataonly.md
new file mode 100644
index 0000000..8a2564c
--- /dev/null
+++ b/docs/markdown/snippets/pkgconfig_dataonly.md
@@ -0,0 +1,15 @@
+## Introduce dataonly for the pkgconfig module
+This allows users to disable writing out the inbuilt variables to
+the pkg-config file as they might actualy not be required.
+
+One reason to have this is for architecture-independent pkg-config
+files in projects which also have architecture-dependent outputs.
+
+```
+pkgg.generate(
+  name : 'libhello_nolib',
+  description : 'A minimalistic pkgconfig file.',
+  version : libver,
+  dataonly: true
+)
+```
diff --git a/mesonbuild/modules/pkgconfig.py b/mesonbuild/modules/pkgconfig.py
index da0a60e..cfdae4f 100644
--- a/mesonbuild/modules/pkgconfig.py
+++ b/mesonbuild/modules/pkgconfig.py
@@ -266,7 +266,7 @@ class PkgConfigModule(ExtensionModule):
 
     def generate_pkgconfig_file(self, state, deps, subdirs, name, description,
                                 url, version, pcfile, conflicts, variables,
-                                uninstalled=False):
+                                uninstalled=False, dataonly=False):
         deps.remove_dups()
         coredata = state.environment.get_coredata()
         if uninstalled:
@@ -283,12 +283,13 @@ class PkgConfigModule(ExtensionModule):
             incdir = PurePath(coredata.get_builtin_option('includedir'))
         fname = os.path.join(outdir, pcfile)
         with open(fname, 'w', encoding='utf-8') as ofile:
-            ofile.write('prefix={}\n'.format(self._escape(prefix)))
-            if uninstalled:
-                ofile.write('srcdir={}\n'.format(self._escape(srcdir)))
-            else:
-                ofile.write('libdir={}\n'.format(self._escape('${prefix}' / libdir)))
-                ofile.write('includedir={}\n'.format(self._escape('${prefix}' / incdir)))
+            if not dataonly:
+                ofile.write('prefix={}\n'.format(self._escape(prefix)))
+                if uninstalled:
+                    ofile.write('srcdir={}\n'.format(self._escape(srcdir)))
+                else:
+                    ofile.write('libdir={}\n'.format(self._escape('${prefix}' / libdir)))
+                    ofile.write('includedir={}\n'.format(self._escape('${prefix}' / incdir)))
             if variables:
                 ofile.write('\n')
             for k, v in variables:
@@ -370,27 +371,28 @@ class PkgConfigModule(ExtensionModule):
                 ofile.write('Libs: {}\n'.format(' '.join(generate_libs_flags(deps.pub_libs))))
             if len(deps.priv_libs) > 0:
                 ofile.write('Libs.private: {}\n'.format(' '.join(generate_libs_flags(deps.priv_libs))))
+
+            def generate_compiler_flags():
+                cflags_buf = []
+                for f in deps.cflags:
+                    cflags_buf.append(self._escape(f))
+                return cflags_buf
+
+            cflags = generate_compiler_flags()
             ofile.write('Cflags:')
             if uninstalled:
                 ofile.write(' '.join(generate_uninstalled_cflags(deps.pub_libs + deps.priv_libs)))
-            else:
-                for h in subdirs:
-                    ofile.write(' ')
-                    if h == '.':
-                        ofile.write('-I${includedir}')
-                    else:
-                        ofile.write(self._escape(PurePath('-I${includedir}') / h))
-            for f in deps.cflags:
-                ofile.write(' ')
-                ofile.write(self._escape(f))
-            ofile.write('\n')
+            elif not dataonly and cflags:
+                ofile.write('{}\n'.format(' '.join(cflags)))
 
     @FeatureNewKwargs('pkgconfig.generate', '0.54.0', ['uninstalled_variables'])
     @FeatureNewKwargs('pkgconfig.generate', '0.42.0', ['extra_cflags'])
     @FeatureNewKwargs('pkgconfig.generate', '0.41.0', ['variables'])
+    @FeatureNewKwargs('pkgconfig.generate', '0.54.0', ['dataonly'])
     @permittedKwargs({'libraries', 'version', 'name', 'description', 'filebase',
                       'subdirs', 'requires', 'requires_private', 'libraries_private',
-                      'install_dir', 'extra_cflags', 'variables', 'url', 'd_module_versions'})
+                      'install_dir', 'extra_cflags', 'variables', 'url', 'd_module_versions',
+                      'dataonly'})
     def generate(self, state, args, kwargs):
         if 'variables' in kwargs:
             FeatureNew('custom pkgconfig variables', '0.41.0').use(state.subproject)
@@ -399,6 +401,7 @@ class PkgConfigModule(ExtensionModule):
         default_description = None
         default_name = None
         mainlib = None
+        default_subdirs = ['.']
         if not args and 'version' not in kwargs:
             FeatureNew('pkgconfig.generate implicit version keyword', '0.46.0').use(state.subproject)
         elif len(args) == 1:
@@ -414,7 +417,14 @@ class PkgConfigModule(ExtensionModule):
         elif len(args) > 1:
             raise mesonlib.MesonException('Too many positional arguments passed to Pkgconfig_gen.')
 
-        subdirs = mesonlib.stringlistify(kwargs.get('subdirs', ['.']))
+        dataonly = kwargs.get('dataonly', False)
+        if dataonly:
+            default_subdirs = []
+            blocked_vars = ['libraries', 'libraries_private', 'require_private', 'extra_cflags', 'subdirs']
+            if len(set(kwargs) & set(blocked_vars)) > 0:
+                raise mesonlib.MesonException('Cannot combine dataonly with any of {}'.format(blocked_vars))
+
+        subdirs = mesonlib.stringlistify(kwargs.get('subdirs', default_subdirs))
         version = kwargs.get('version', default_version)
         if not isinstance(version, str):
             raise mesonlib.MesonException('Version must be specified.')
@@ -440,6 +450,11 @@ class PkgConfigModule(ExtensionModule):
             libraries = [mainlib] + libraries
 
         deps = DependenciesHelper(state, filebase)
+        for d in subdirs:
+            if d == '.':
+                deps.add_cflags(['-I${includedir}'])
+            else:
+                deps.add_cflags(self._escape(PurePath('-I${includedir}') / d))
         deps.add_pub_libs(libraries)
         deps.add_priv_libs(kwargs.get('libraries_private', []))
         deps.add_pub_reqs(kwargs.get('requires', []))
@@ -488,13 +503,14 @@ class PkgConfigModule(ExtensionModule):
         if not isinstance(pkgroot, str):
             raise mesonlib.MesonException('Install_dir must be a string.')
         self.generate_pkgconfig_file(state, deps, subdirs, name, description, url,
-                                     version, pcfile, conflicts, variables)
+                                     version, pcfile, conflicts, variables,
+                                     False, dataonly)
         res = build.Data(mesonlib.File(True, state.environment.get_scratch_dir(), pcfile), pkgroot)
         variables = parse_variable_list(mesonlib.stringlistify(kwargs.get('uninstalled_variables', [])))
         pcfile = filebase + '-uninstalled.pc'
         self.generate_pkgconfig_file(state, deps, subdirs, name, description, url,
                                      version, pcfile, conflicts, variables,
-                                     uninstalled=True)
+                                     uninstalled=True, dataonly=dataonly)
         # Associate the main library with this generated pc file. If the library
         # is used in any subsequent call to the generated, it will generate a
         # 'Requires:' or 'Requires.private:'.
diff --git a/run_unittests.py b/run_unittests.py
index 7c2ae05..69de23a 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -4969,6 +4969,11 @@ class LinuxlikeTests(BasePlatformTests):
         self.assertEqual(foo_dep.get_pkgconfig_variable('foo', {}), 'bar')
         self.assertPathEqual(foo_dep.get_pkgconfig_variable('datadir', {}), '/usr/data')
 
+        libhello_nolib = PkgConfigDependency('libhello_nolib', env, kwargs)
+        self.assertTrue(libhello_nolib.found())
+        self.assertEqual(libhello_nolib.get_link_args(), [])
+        self.assertEqual(libhello_nolib.get_compile_args(), [])
+
     def test_pkgconfig_gen_deps(self):
         '''
         Test that generated pkg-config files correctly handle dependencies
diff --git a/test cases/common/47 pkgconfig-gen/installed_files.txt b/test cases/common/47 pkgconfig-gen/installed_files.txt
index 94de704..9e1a40a 100644
--- a/test cases/common/47 pkgconfig-gen/installed_files.txt
+++ b/test cases/common/47 pkgconfig-gen/installed_files.txt
@@ -2,3 +2,4 @@ usr/include/simple.h
 usr/lib/pkgconfig/simple.pc
 usr/lib/pkgconfig/libfoo.pc
 usr/lib/pkgconfig/libhello.pc
+usr/lib/pkgconfig/libhello_nolib.pc
\ No newline at end of file
diff --git a/test cases/common/47 pkgconfig-gen/meson.build b/test cases/common/47 pkgconfig-gen/meson.build
index 09c46c5..c251b9f 100644
--- a/test cases/common/47 pkgconfig-gen/meson.build
+++ b/test cases/common/47 pkgconfig-gen/meson.build
@@ -51,3 +51,10 @@ pkgg.generate(
   description : 'A minimalistic pkgconfig file.',
   version : libver,
 )
+
+pkgg.generate(
+  name : 'libhello_nolib',
+  description : 'A minimalistic pkgconfig file.',
+  version : libver,
+  dataonly: true
+)