gtk: add localization support, take 3 (#6004)

This is my third (!) attempt at implementing localization support. By
leveraging GTK builder to do most of the `gettext` calls, I can avoid
the whole mess about missing symbols on non-glibc platforms.

Added some documentation too for contributors and translators, just for
good measure.

Supersedes #5214, resolves the GTK half of #2357

src/build/GhosttyI18n.zig

@@ -0,0 +1,118 @@
+const GhosttyI18n = @This();
+
+const std = @import("std");
+const Config = @import("Config.zig");
+const gresource = @import("../apprt/gtk/gresource.zig");
+
+const domain = "com.mitchellh.ghostty";
+
+const locales = [_][]const u8{
+    "zh_CN.UTF-8",
+};
+
+owner: *std.Build,
+steps: []*std.Build.Step,
+
+/// This step updates the translation files on disk that should be
+/// committed to the repo.
+update_step: *std.Build.Step,
+
+pub fn init(b: *std.Build, cfg: *const Config) !GhosttyI18n {
+    var steps = std.ArrayList(*std.Build.Step).init(b.allocator);
+    defer steps.deinit();
+
+    if (cfg.app_runtime == .gtk) {
+        // Output the .mo files used by the GTK apprt
+        inline for (locales) |locale| {
+            const msgfmt = b.addSystemCommand(&.{ "msgfmt", "-o", "-" });
+            msgfmt.addFileArg(b.path("po/" ++ locale ++ ".po"));
+
+            try steps.append(&b.addInstallFile(
+                msgfmt.captureStdOut(),
+                std.fmt.comptimePrint(
+                    "share/locale/{s}/LC_MESSAGES/{s}.mo",
+                    .{ locale, domain },
+                ),
+            ).step);
+        }
+    }
+
+    return .{
+        .owner = b,
+        .update_step = try createUpdateStep(b),
+        .steps = try steps.toOwnedSlice(),
+    };
+}
+
+pub fn install(self: *const GhosttyI18n) void {
+    for (self.steps) |step| self.owner.getInstallStep().dependOn(step);
+}
+
+fn createUpdateStep(b: *std.Build) !*std.Build.Step {
+    const xgettext = b.addSystemCommand(&.{
+        "xgettext",
+        "--language=C", // Silence the "unknown extension" errors
+        "--from-code=UTF-8",
+        "--add-comments=Translators",
+        "--keyword=_",
+        "--keyword=C_:1c,2",
+        "--package-name=" ++ domain,
+        "--msgid-bugs-address=m@mitchellh.com",
+        "--copyright-holder=Mitchell Hashimoto",
+        "-o",
+        "-",
+    });
+
+    // Not cacheable due to the gresource files
+    xgettext.has_side_effects = true;
+
+    inline for (gresource.blueprint_files) |blp| {
+        // We avoid using addFileArg here since the full, absolute file path
+        // would be added to the file as its location, which differs for
+        // everyone's checkout of the repository.
+        // This comes at a cost of losing per-file caching, of course.
+        xgettext.addArg(std.fmt.comptimePrint(
+            "src/apprt/gtk/ui/{[major]}.{[minor]}/{[name]s}.blp",
+            blp,
+        ));
+    }
+
+    {
+        var gtk_files = try b.build_root.handle.openDir(
+            "src/apprt/gtk",
+            .{ .iterate = true },
+        );
+        defer gtk_files.close();
+
+        var walk = try gtk_files.walk(b.allocator);
+        defer walk.deinit();
+        while (try walk.next()) |src| {
+            switch (src.kind) {
+                .file => if (!std.mem.endsWith(
+                    u8,
+                    src.basename,
+                    ".zig",
+                )) continue,
+
+                else => continue,
+            }
+
+            xgettext.addArg((b.pathJoin(&.{ "src/apprt/gtk", src.path })));
+        }
+    }
+
+    const wf = b.addWriteFiles();
+    wf.addCopyFileToSource(
+        xgettext.captureStdOut(),
+        "po/" ++ domain ++ ".pot",
+    );
+
+    inline for (locales) |locale| {
+        const msgmerge = b.addSystemCommand(&.{ "msgmerge", "-q" });
+        msgmerge.addFileArg(b.path("po/" ++ locale ++ ".po"));
+        msgmerge.addFileArg(xgettext.captureStdOut());
+        wf.addCopyFileToSource(msgmerge.captureStdOut(), "po/" ++ locale ++ ".po");
+    }
+
+    return &wf.step;
+}

src/build/docker/debian/Dockerfile

@@ -40,6 +40,7 @@ COPY ./dist/linux /src/dist/linux
 COPY ./images /src/images
 COPY ./include /src/include
 COPY ./pkg /src/pkg
+COPY ./po /src/po
 COPY ./nix /src/nix
 COPY ./vendor /src/vendor
 COPY ./build.zig /src/build.zig

src/build/main.zig

@@ -13,6 +13,7 @@ pub const GhosttyExe = @import("GhosttyExe.zig");
 pub const GhosttyFrameData = @import("GhosttyFrameData.zig");
 pub const GhosttyLib = @import("GhosttyLib.zig");
 pub const GhosttyResources = @import("GhosttyResources.zig");
+pub const GhosttyI18n = @import("GhosttyI18n.zig");
 pub const GhosttyXCFramework = @import("GhosttyXCFramework.zig");
 pub const GhosttyWebdata = @import("GhosttyWebdata.zig");
 pub const HelpStrings = @import("HelpStrings.zig");