gtk: build gtk4-layer-shell ourselves

As of now `gtk4-layer-shell` is unavailable on recent, stable releases
of many distros (Debian 12, Ubuntu 24.04, openSUSE Leap & Tumbleweed, etc.)
and outdated on many others (Nixpkgs 24.11/unstable, Fedora 41, etc.)
This is inconvenient for our users and severely limits where the quick
terminal can be used. As a result we then build gtk4-layer-shell ourselves
by default unless `--system` or `-fsys=gtk4-layer-shell` are specified.
This also allows me to add an idiomatic Zig API on top of the library
and avoiding adding even more raw C code in the GTK apprt.

Since we now build gtk4-layer-shell it should be theoretically available
on all Linux systems we target. As such, the `-Dgtk-layer-shell` build
option has been removed. This is somewhat of an experimental change as
I don't know if gtk4-layer-shell works perfectly across all distros, and
we can always add the option back if need be.

src/build/Config.zig

@@ -34,7 +34,6 @@ font_backend: font.Backend = .freetype,
 /// Feature flags
 x11: bool = false,
 wayland: bool = false,
-layer_shell: bool = false,
 sentry: bool = true,
 wasm_shared: bool = true,
 
@@ -163,12 +162,6 @@ pub fn init(b: *std.Build) !Config {
         "Enables linking against X11 libraries when using the GTK rendering backend.",
     ) orelse gtk_targets.x11;
 
-    config.layer_shell = b.option(
-        bool,
-        "gtk-layer-shell",
-        "Enables linking against the gtk4-layer-shell library for quick terminal support. Requires Wayland.",
-    ) orelse gtk_targets.layer_shell;
-
     //---------------------------------------------------------------
     // Ghostty Exe Properties
 
@@ -366,6 +359,7 @@ pub fn init(b: *std.Build) !Config {
             "libpng",
             "zlib",
             "oniguruma",
+            "gtk4-layer-shell",
         }) |dep| {
             _ = b.systemIntegrationOption(
                 dep,
@@ -398,7 +392,6 @@ pub fn addOptions(self: *const Config, step: *std.Build.Step.Options) !void {
     step.addOption(bool, "flatpak", self.flatpak);
     step.addOption(bool, "x11", self.x11);
     step.addOption(bool, "wayland", self.wayland);
-    step.addOption(bool, "layer_shell", self.layer_shell);
     step.addOption(bool, "sentry", self.sentry);
     step.addOption(apprt.Runtime, "app_runtime", self.app_runtime);
     step.addOption(font.Backend, "font_backend", self.font_backend);

src/build/SharedDeps.zig

@@ -484,7 +484,24 @@ pub fn add(
                     step.root_module.addImport("wayland", wayland);
                     step.root_module.addImport("gdk_wayland", gobject.module("gdkwayland4"));
 
-                    if (self.config.layer_shell) step.linkSystemLibrary2("gtk4-layer-shell", dynamic_link_opts);
+                    const gtk4_layer_shell = b.dependency("gtk4_layer_shell", .{
+                        .target = target,
+                        .optimize = optimize,
+                    });
+                    const layer_shell_module = gtk4_layer_shell.module("gtk4-layer-shell");
+                    layer_shell_module.addImport("gtk", gobject.module("gtk4"));
+                    step.root_module.addImport("gtk4-layer-shell", layer_shell_module);
+
+                    // IMPORTANT: gtk4-layer-shell must be linked BEFORE
+                    // wayland-client, as it relies on shimming libwayland's APIs.
+                    if (b.systemIntegrationOption("gtk4-layer-shell", .{})) {
+                        step.linkSystemLibrary2("gtk4-layer-shell", dynamic_link_opts);
+                    } else {
+                        // gtk4-layer-shell *must* be dynamically linked,
+                        // so we don't add it as a static library
+                        step.linkLibrary(gtk4_layer_shell.artifact("gtk4-layer-shell"));
+                    }
+
                     step.linkSystemLibrary2("wayland-client", dynamic_link_opts);
                 }
 

src/build/docker/debian/Dockerfile

@@ -51,5 +51,6 @@ RUN ZIG_GLOBAL_CACHE_DIR=/zig/global-cache ./nix/build-support/fetch-zig-cache.s
 
 COPY ./src /src/src
 
-RUN zig build -Doptimize=Debug -Dcpu=baseline -Dapp-runtime=gtk --system /zig/global-cache/p
+# Debian 12 doesn't have gtk4-layer-shell, so we have to manually compile it ourselves
+RUN zig build -Doptimize=Debug -Dcpu=baseline -Dapp-runtime=gtk -fno-sys=gtk4-layer-shell --system /zig/global-cache/p
 

src/build/gtk.zig

@@ -3,7 +3,6 @@ const std = @import("std");
 pub const Targets = packed struct {
     x11: bool = false,
     wayland: bool = false,
-    layer_shell: bool = false,
 };
 
 /// Returns the targets that GTK4 was compiled with.
@@ -21,21 +20,8 @@ pub fn targets(b: *std.Build) Targets {
     const x11 = std.mem.indexOf(u8, output, "x11") != null;
     const wayland = std.mem.indexOf(u8, output, "wayland") != null;
 
-    const layer_shell = layer_shell: {
-        if (!wayland) break :layer_shell false;
-
-        _ = b.runAllowFail(
-            &.{ "pkg-config", "--exists", "gtk4-layer-shell-0" },
-            &code,
-            .Ignore,
-        ) catch break :layer_shell false;
-
-        break :layer_shell true;
-    };
-
     return .{
         .x11 = x11,
         .wayland = wayland,
-        .layer_shell = layer_shell,
     };
 }