gtkdoc: Fix dependencies not being built before invoking gtkdoc

In GLib when running "ninja gio-doc" without doing a full build first,
it won't build libraries and the generated gio-scan.c gets linked
against system libgio instead.

This fix 2 bugs: gtkdoc() was not passing 'depends' variable down to
_get_dependencies_flags(), and many places had 'if depends' which is
False when 'depends' is an empty list and not only when it's None. There
is no reason for that argument to be optional, we always want to collect
dependencies.

mesonbuild/modules/gnome.py

@@ -288,7 +288,7 @@ class GnomeModule(ExtensionModule):
                 dep_files.append(f)
         return dep_files, depends, subdirs
 
-    def _get_link_args(self, state, lib, depends=None, include_rpath=False,
+    def _get_link_args(self, state, lib, depends, include_rpath=False,
                        use_gir_args=False):
         link_command = []
         # Construct link args
@@ -306,15 +306,14 @@ class GnomeModule(ExtensionModule):
                     link_command.append('-Wl,-rpath,' + d)
             if include_rpath:
                 link_command.append('-Wl,-rpath,' + libdir)
-            if depends:
+            depends.append(lib)
-                depends.append(lib)
         if gir_has_extra_lib_arg(self.interpreter) and use_gir_args:
             link_command.append('--extra-library=' + lib.name)
         else:
             link_command.append('-l' + lib.name)
         return link_command
 
-    def _get_dependencies_flags(self, deps, state, depends=None, include_rpath=False,
+    def _get_dependencies_flags(self, deps, state, depends, include_rpath=False,
                                 use_gir_args=False):
         cflags = OrderedSet()
         ldflags = OrderedSet()
@@ -371,6 +370,7 @@ class GnomeModule(ExtensionModule):
                         gi_includes.update([girdir])
             elif isinstance(dep, (build.StaticLibrary, build.SharedLibrary)):
                 cflags.update(get_include_args(dep.get_include_dirs()))
+                depends.append(dep)
             else:
                 mlog.log('dependency {!r} not handled to build gir files'.format(dep))
                 continue
@@ -823,16 +823,16 @@ This will become a hard error in the future.''')
         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)
+        args += self._get_build_args(kwargs, state, depends)
         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)
 
-    def _get_build_args(self, kwargs, state):
+    def _get_build_args(self, kwargs, state, depends):
         args = []
         deps = extract_as_list(kwargs, 'dependencies', unholder=True)
-        cflags, ldflags, gi_includes = self._get_dependencies_flags(deps, state, include_rpath=True)
+        cflags, ldflags, gi_includes = self._get_dependencies_flags(deps, state, depends, include_rpath=True)
         inc_dirs = mesonlib.extract_as_list(kwargs, 'include_directories')
         for incd in inc_dirs:
             if not isinstance(incd.held_object, (str, build.IncludeDirs)):