gnome.gtkdoc: Add dependencies over generated targets

The gtkdoc function can also use generated targets to create
documentation. However, the dependencies over these generated files
are missing, so these must be also included in the run target.

mesonbuild/modules/gnome.py

@@ -777,32 +777,38 @@ This will become a hard error in the future.''')
         args += self._unpack_args('--mkdbargs=', 'mkdb_args', kwargs)
         args += self._unpack_args('--html-assets=', 'html_assets', kwargs, state)
 
+        depends = []
         content_files = []
         for s in mesonlib.extract_as_list(kwargs, 'content_files'):
             if hasattr(s, 'held_object'):
                 s = s.held_object
             if isinstance(s, (build.CustomTarget, build.CustomTargetIndex)):
+                depends.append(s)
                 content_files.append(os.path.join(state.environment.get_build_dir(),
                                                   state.backend.get_target_dir(s),
                                                   s.get_outputs()[0]))
             elif isinstance(s, mesonlib.File):
                 content_files.append(s.rel_to_builddir(state.build_to_src))
             elif isinstance(s, build.GeneratedList):
+                depends.append(s)
                 for gen_src in s.get_outputs():
                     content_files.append(os.path.join(state.environment.get_source_dir(),
                                                       state.subdir,
                                                       gen_src))
-            else:
+            elif isinstance(s, str):
                 content_files.append(os.path.join(state.environment.get_source_dir(),
                                                   state.subdir,
                                                   s))
+            else:
+                raise MesonException(
+                    'Invalid object type: {!r}'.format(s.__class__.__name__))
         args += ['--content-files=' + '@@'.join(content_files)]
 
         args += self._unpack_args('--expand-content-files=', 'expand_content_files', kwargs, state)
         args += self._unpack_args('--ignore-headers=', 'ignore_headers', kwargs)
         args += self._unpack_args('--installdir=', 'install_dir', kwargs, state)
         args += self._get_build_args(kwargs, state)
-        res = [build.RunTarget(targetname, command[0], command[1:] + args, [], state.subdir, state.subproject)]
+        res = [build.RunTarget(targetname, command[0], command[1:] + args, depends, state.subdir, state.subproject)]
         if kwargs.get('install', True):
             res.append(build.RunScript(command, args))
         return ModuleReturnValue(None, res)