zig build dist and distcheck for source tarballs

This moves the source tarball creation process into the Zig build system
and follows the autotools-standard naming conventions of `dist` and
`distcheck`.

The `dist` target creates a source tarball in the `PREFIX/dist`
directory. The tarball is named `ghostty-VERSION.tar.gz` as expected by
standard source tarball conventions.

The `distcheck` target does the same as `dist`, but also takes the
resulting tarball, extracts it, and runs tests on the extracted source
to verify the source tarball works as expected.

This commit also updates CI:

  1. Tagged releases now use the new `zig build distcheck` command.
  2. Tip releases now use the new `zig build dist` command.
  3. A new test build tests that source tarball generation works on
     every commit.

src/build/GhosttyDist.zig

@@ -0,0 +1,87 @@
+const GhosttyDist = @This();
+
+const std = @import("std");
+const Config = @import("Config.zig");
+const SharedDeps = @import("SharedDeps.zig");
+
+/// The final source tarball.
+archive: std.Build.LazyPath,
+
+/// The step to install the tarball.
+install_step: *std.Build.Step,
+
+/// The step to depend on
+archive_step: *std.Build.Step,
+
+/// The step to depend on for checking the dist
+check_step: *std.Build.Step,
+
+pub fn init(b: *std.Build, cfg: *const Config) !GhosttyDist {
+    // git archive to create the final tarball. "git archive" is the
+    // easiest way I can find to create a tarball that ignores stuff
+    // from gitignore and also supports adding files as well as removing
+    // dist-only files (the "export-ignore" git attribute).
+    const git_archive = b.addSystemCommand(&.{
+        "git",
+        "archive",
+        "--format=tgz",
+
+        // This is important. Standard source tarballs extract into
+        // a directory named `project-version`. This is expected by
+        // standard tooling such as debhelper and rpmbuild.
+        b.fmt("--prefix=ghostty-{}/", .{cfg.version}),
+
+        "-o",
+    });
+    const output = git_archive.addOutputFileArg(b.fmt(
+        "ghostty-{}.tar.gz",
+        .{cfg.version},
+    ));
+    git_archive.addArg("HEAD");
+
+    // The install step to put the dist into the build directory.
+    const install = b.addInstallFile(
+        output,
+        b.fmt("dist/ghostty-{}.tar.gz", .{cfg.version}),
+    );
+
+    // The check step to ensure the archive works.
+    const check = b.addSystemCommand(&.{ "tar", "xvzf" });
+    check.addFileArg(output);
+    check.addArg("-C");
+
+    // This is the root Ghostty source dir of the extracted source tarball.
+    // i.e. this is way `build.zig` is.
+    const extract_dir = check
+        .addOutputDirectoryArg("ghostty")
+        .path(b, b.fmt("ghostty-{}", .{cfg.version}));
+
+    // Check that tests pass within the extracted directory. This isn't
+    // a fully hermetic test because we're sharing the Zig cache. In
+    // the future we could add an option to use a totally new cache but
+    // in the interest of speed we don't do that for now and hope other
+    // CI catches any issues.
+    const check_test = step: {
+        const step = b.addSystemCommand(&.{ "zig", "build", "test" });
+        step.setCwd(extract_dir);
+
+        // Must be set so that Zig knows that this command doesn't
+        // have side effects and is being run for its exit code check.
+        // Zig will cache depending on its extract dir.
+        step.expectExitCode(0);
+
+        // Capture stderr so it doesn't spew into the parent build.
+        // On the flip side, if the test fails we won't know why so
+        // that sucks but we should have already ran tests at this point.
+        _ = step.captureStdErr();
+
+        break :step step;
+    };
+
+    return .{
+        .archive = output,
+        .install_step = &install.step,
+        .archive_step = &git_archive.step,
+        .check_step = &check_test.step,
+    };
+}

src/build/main.zig

@@ -8,6 +8,7 @@ pub const GitVersion = @import("GitVersion.zig");
 
 // Artifacts
 pub const GhosttyBench = @import("GhosttyBench.zig");
+pub const GhosttyDist = @import("GhosttyDist.zig");
 pub const GhosttyDocs = @import("GhosttyDocs.zig");
 pub const GhosttyExe = @import("GhosttyExe.zig");
 pub const GhosttyFrameData = @import("GhosttyFrameData.zig");