stage2: implement zig version

build.zig

@@ -10,6 +10,8 @@ const io = std.io;
 const fs = std.fs;
 const InstallDirectoryOptions = std.build.InstallDirectoryOptions;
 
+const zig_version = std.builtin.Version{ .major = 0, .minor = 6, .patch = 0 };
+
 pub fn build(b: *Builder) !void {
     b.setPreferredReleaseMode(.ReleaseFast);
     const mode = b.standardReleaseOptions();
@@ -79,6 +81,24 @@ pub fn build(b: *Builder) !void {
 
         const log_scopes = b.option([]const []const u8, "log", "Which log scopes to enable") orelse &[0][]const u8{};
 
+        const opt_version_string = b.option([]const u8, "version-string", "Override Zig version string. Default is to find out with git.");
+        const version = if (opt_version_string) |version| version else v: {
+            var code: u8 = undefined;
+            const version_untrimmed = b.execAllowFail(&[_][]const u8{
+                "git",    "-C",          b.build_root,     "name-rev", "HEAD",
+                "--tags", "--name-only", "--no-undefined", "--always",
+            }, &code, .Ignore) catch |err| {
+                std.debug.print(
+                    \\Unable to determine zig version string: {}
+                    \\Provide the zig version string explicitly using the `version-string` build option.
+                , .{err});
+                std.process.exit(1);
+            };
+            const trimmed = mem.trim(u8, version_untrimmed, " \n\r");
+            break :v b.fmt("{}.{}.{}+{}", .{ zig_version.major, zig_version.minor, zig_version.patch, trimmed });
+        };
+        exe.addBuildOption([]const u8, "version", version);
+
         exe.addBuildOption([]const []const u8, "log_scopes", log_scopes);
         exe.addBuildOption(bool, "enable_tracy", tracy != null);
         if (tracy) |tracy_path| {

src-self-hosted/link.zig

@@ -15,6 +15,9 @@ const leb128 = std.debug.leb;
 const Package = @import("Package.zig");
 const Value = @import("value.zig").Value;
 const Type = @import("type.zig").Type;
+const build_options = @import("build_options");
+
+const producer_string = if (std.builtin.is_test) "zig test" else "zig " ++ build_options.version;
 
 // TODO Turn back on zig fmt when https://github.com/ziglang/zig/issues/5948 is implemented.
 // zig fmt: off
@@ -1132,7 +1135,7 @@ pub const File = struct {
                 // Write the form for the compile unit, which must match the abbrev table above.
                 const name_strp = try self.makeDebugString(self.base.options.root_pkg.root_src_path);
                 const comp_dir_strp = try self.makeDebugString(self.base.options.root_pkg.root_src_dir_path);
-                const producer_strp = try self.makeDebugString("zig (TODO version here)");
+                const producer_strp = try self.makeDebugString(producer_string);
                 // Currently only one compilation unit is supported, so the address range is simply
                 // identical to the main program header virtual address and memory size.
                 const text_phdr = &self.program_headers.items[self.phdr_load_re_index.?];

src-self-hosted/main.zig

@@ -95,11 +95,8 @@ pub fn main() !void {
         const stdout = io.getStdOut().outStream();
         return @import("print_targets.zig").cmdTargets(arena, cmd_args, stdout, info.target);
     } else if (mem.eql(u8, cmd, "version")) {
-        // Need to set up the build script to give the version as a comptime value.
-        // TODO when you solve this, also take a look at link.zig, there is a placeholder
-        // that says "TODO version here".
-        std.debug.print("TODO version command not implemented yet\n", .{});
-        return error.Unimplemented;
+        std.io.getStdOut().writeAll(build_options.version ++ "\n") catch process.exit(1);
+        return;
     } else if (mem.eql(u8, cmd, "zen")) {
         try io.getStdOut().writeAll(info_zen);
     } else if (mem.eql(u8, cmd, "help")) {