Pass --gresources to valac for each compiled gresource

Without this, the user has to both compile the resource with
gnome.compile_resources, pass that to the target sources, and also
pass --gresources=/path/to/gres.xml to vala_args in the target.

With this, we will do that automatically.

mesonbuild/backend/backends.py

@@ -504,19 +504,13 @@ class Backend():
                     libs.append(os.path.join(self.get_target_dir(t), f))
         return libs
 
-    def eval_custom_target_command(self, target, absolute_paths=False):
-        if not absolute_paths:
-            ofilenames = [os.path.join(self.get_target_dir(target), i) for i in target.output]
-        else:
-            ofilenames = [os.path.join(self.environment.get_build_dir(), self.get_target_dir(target), i) \
-                          for i in target.output]
+    def get_custom_target_sources(self, target, absolute_paths=False):
+        '''
+        Custom target sources can be of various object types; strings, File,
+        BuildTarget, even other CustomTargets.
+        Returns the path to them relative to the build root directory.
+        '''
         srcs = []
-        outdir = self.get_target_dir(target)
-        # Many external programs fail on empty arguments.
-        if outdir == '':
-            outdir = '.'
-        if absolute_paths:
-            outdir = os.path.join(self.environment.get_build_dir(), outdir)
         for i in target.get_sources():
             if hasattr(i, 'held_object'):
                 i = i.held_object
@@ -531,8 +525,23 @@ class Backend():
             else:
                 fname = [i.rel_to_builddir(self.build_to_src)]
             if absolute_paths:
-                fname =[os.path.join(self.environment.get_build_dir(), f) for f in fname]
+                fname = [os.path.join(self.environment.get_build_dir(), f) for f in fname]
             srcs += fname
+        return srcs
+
+    def eval_custom_target_command(self, target, absolute_paths=False):
+        if not absolute_paths:
+            ofilenames = [os.path.join(self.get_target_dir(target), i) for i in target.output]
+        else:
+            ofilenames = [os.path.join(self.environment.get_build_dir(), self.get_target_dir(target), i) \
+                          for i in target.output]
+        srcs = self.get_custom_target_sources(target, absolute_paths)
+        outdir = self.get_target_dir(target)
+        # Many external programs fail on empty arguments.
+        if outdir == '':
+            outdir = '.'
+        if absolute_paths:
+            outdir = os.path.join(self.environment.get_build_dir(), outdir)
         cmd = []
         for i in target.command:
             if isinstance(i, build.Executable):

mesonbuild/backend/ninjabackend.py

@@ -1032,6 +1032,11 @@ int dummy;
                 args += ['--pkg', d.name]
             elif isinstance(d, dependencies.ExternalLibrary):
                 args += d.get_lang_args('vala')
+        # Detect gresources and add --gresources arguments for each
+        for (gres, gensrc) in other_src[1].items():
+            if hasattr(gensrc, 'gresource_c_output'):
+                gres_xml, = self.get_custom_target_sources(gensrc)
+                args += ['--gresources=' + gres_xml]
         extra_args = []
 
         for a in target.extra_args.get('vala', []):

mesonbuild/modules/gnome.py

@@ -162,6 +162,9 @@ can not be used with the current version of glib-compiled-resources, due to
             kwargs['depfile'] = depfile
             kwargs['command'] = copy.copy(cmd) + ['--dependency-file', '@DEPFILE@']
         target_c = build.CustomTarget(name, state.subdir, kwargs)
+        # Used in backend/ninjabackend.py:generate_vala_compile() to pass
+        # --gresources to valac when GResources are used in Vala targets
+        target_c.gresource_c_output = True
 
         if gresource: # Only one target for .gresource files
             return [target_c]