docs: Add initial support for using gi-docgen for docs

The files here are copied from the docs-gtk-org
branch of gtk.

This adds gi-docgen to the CI Dockerfiles and ensures the new versions
(including the OS upgrades from the previous commit) are used during CI.

Helps: #3037

docs/reference/gobject/gobject.toml.in

@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+# Copyright 2023 Matthias Clasen
+# Copyright 2023 Philip Withnall
+
+[library]
+name = "GObject"
+version = "@VERSION@"
+browse_url = "https://gitlab.gnome.org/GNOME/glib/"
+repository_url = "https://gitlab.gnome.org/GNOME/glib.git"
+website_url = "https://www.gtk.org"
+docs_url = "https://docs.gtk.org/gobject/"
+authors = "GLib Development Team"
+license = "LGPL-2.1-or-later"
+description = "The base type system and object class"
+devhelp = true
+search_index = true
+dependencies = ["GLib-2.0"]
+
+  [dependencies."GLib-2.0"]
+  name = "GLib"
+  description = "The base utility library"
+  docs_url = "https://docs.gtk.org/glib/"
+
+related = ["GModule-2.0", "Gio-2.0"]
+
+  [related."GModule-2.0"]
+  name = "GModule"
+  description = "Portable API for dynamically loading modules"
+  docs_url = "https://docs.gtk.org/gmodule/"
+
+  [related."Gio-2.0"]
+  name = "GIO"
+  description = "GObject Interfaces and Objects, Networking, IPC, and I/O"
+  docs_url = "https://docs.gtk.org/gio/"
+
+[theme]
+name = "basic"
+show_index_summary = true
+show_class_hierarchy = true
+
+[extra]
+urlmap_file = "urlmap.js"
+# The same order will be used when generating the index
+content_files = [
+]
+content_images = [
+]
+
+# This is the anonymous union inside GValue; we don't need it
+# as a type, and including it just generates a dummy union
+# definition
+[[object]]
+name = "_Value__data__union"
+hidden = true

docs/reference/gobject/meson.build

@@ -68,3 +68,27 @@ if get_option('man')
       install_dir: man1_dir)
   endforeach
 endif
+
+# gi-docgen version
+expand_content_files = [
+]
+
+gobject_gir = meson.current_source_dir() / 'GObject-2.0.gir'
+gobject_toml = configure_file(input: 'gobject.toml.in', output: 'gobject.toml', configuration: toml_conf)
+
+custom_target('gobject-docs',
+  input: [ gobject_toml, gobject_gir ],
+  output: 'gobject',
+  command: [
+    gidocgen,
+    'generate',
+    gidocgen_common_args,
+    '--config=@INPUT0@',
+    '--output-dir=@OUTPUT@',
+    '--content-dir=@0@'.format(meson.current_source_dir()),
+    '--add-include-path=@0@'.format(meson.current_source_dir() / '../glib'),
+    '@INPUT1@',
+  ],
+  build_by_default: true,
+  depend_files: expand_content_files,
+)

docs/reference/gobject/urlmap.js

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+// SPDX-FileCopyrightText: 2023 Matthias Clasen
+var baseURLs = [
+    [ 'GLib', 'https://docs.gtk.org/glib/' ],
+    [ 'GModule', 'https://docs.gtk.org/gmodule/' ],
+    [ 'GObject', 'https://docs.gtk.org/gobject/' ],
+    [ 'Gio', 'https://docs.gtk.org/gio/' ],
+    [ 'Gtk', 'https://docs.gtk.org/gtk4/' ],
+];