gtk: introduce Zig bindings for GTK/GObject (#5560)

`zig-gobject` is a set of GObject bindings that allow us to write
GTK-facing code in Zig instead of getting hands dirty with C. It's been
tested and refined in real-life applications and several GTK
contributors agree that it is a marked improvement over using the C API
directly, such as allowing method call syntax and avoiding many manual
`@ptrCast`s.

This PR doesn't actually contain any changes to our preexisting GTK code
— the migration process is intended to begin in chunks, firstly in
self-contained components (e.g. the header bar, overlays, etc.), and
then full-scale migration can begin when we remove non-Adwaita GTK
builds for 1.2. (After all, why port code that you'll remove later
either way?)

build.zig.zon

@@ -41,6 +41,10 @@
             .url = "git+https://github.com/natecraddock/zf/?ref=main#ed99ca18b02dda052e20ba467e90b623c04690dd",
             .hash = "1220edc3b8d8bedbb50555947987e5e8e2f93871ca3c8e8d4cc8f1377c15b5dd35e8",
         },
+        .gobject = .{
+            .url = "https://github.com/ianprime0509/zig-gobject/releases/download/v0.2.2/bindings-gnome47.tar.zst",
+            .hash = "12208d70ee791d7ef7e16e1c3c9c1127b57f1ed066a24f87d57fc9f730c5dc394b9d",
+        },
 
         // C libs
         .cimgui = .{ .path = "./pkg/cimgui" },

nix/devShell.nix

@@ -30,6 +30,7 @@
   glib,
   glslang,
   gtk4,
+  gobject-introspection,
   libadwaita,
   adwaita-icon-theme,
   hicolor-icon-theme,
@@ -83,6 +84,7 @@
       libadwaita
       gtk4
       glib
+      gobject-introspection
       wayland
     ];
 in
@@ -157,6 +159,7 @@ in
         libadwaita
         gtk4
         glib
+        gobject-introspection
         wayland
         wayland-scanner
         wayland-protocols

nix/package.nix

@@ -12,6 +12,7 @@
   libGL,
   glib,
   gtk4,
+  gobject-introspection,
   libadwaita,
   wrapGAppsHook4,
   gsettings-desktop-schemas,
@@ -124,6 +125,7 @@ in
         pandoc
         pkg-config
         zig_hook
+        gobject-introspection
         wrapGAppsHook4
       ]
       ++ lib.optionals enableWayland [

nix/zigCacheHash.nix

@@ -1,3 +1,3 @@
 # This file is auto-generated! check build-support/check-zig-cache-hash.sh for
 # more details.
-"sha256-I7uuv0MkaW3gWAw6NHci+II42OfM7NdtKh2Npw2pTis="
+"sha256-+Ag900R3lDV7iEeRFGe2HWJDtquW3I9GFvHGle+U3k0="

src/build/SharedDeps.zig

@@ -430,9 +430,32 @@ pub fn add(
             },
 
             .gtk => {
+                const gobject = b.dependency("gobject", .{
+                    .target = target,
+                    .optimize = optimize,
+                });
+                const gobject_imports = .{
+                    .{ "gobject", "gobject2" },
+                    .{ "glib", "glib2" },
+                    .{ "gtk", "gtk4" },
+                    .{ "gdk", "gdk4" },
+                };
+                inline for (gobject_imports) |import| {
+                    const name, const module = import;
+                    step.root_module.addImport(name, gobject.module(module));
+                }
+
                 step.linkSystemLibrary2("gtk4", dynamic_link_opts);
-                if (self.config.adwaita) step.linkSystemLibrary2("libadwaita-1", dynamic_link_opts);
-                if (self.config.x11) step.linkSystemLibrary2("X11", dynamic_link_opts);
+
+                if (self.config.adwaita) {
+                    step.linkSystemLibrary2("libadwaita-1", dynamic_link_opts);
+                    step.root_module.addImport("adw", gobject.module("adw1"));
+                }
+
+                if (self.config.x11) {
+                    step.linkSystemLibrary2("X11", dynamic_link_opts);
+                    step.root_module.addImport("gdk_x11", gobject.module("gdkx114"));
+                }
 
                 if (self.config.wayland) {
                     const scanner = Scanner.create(b.dependency("zig_wayland", .{}), .{
@@ -460,6 +483,7 @@ pub fn add(
                     scanner.generate("org_kde_kwin_server_decoration_manager", 1);
 
                     step.root_module.addImport("wayland", wayland);
+                    step.root_module.addImport("gdk_wayland", gobject.module("gdkwayland4"));
                     step.linkSystemLibrary2("wayland-client", dynamic_link_opts);
                 }