Record the Ruby bench version in the output artifacts

lib/benchmark_runner.rb

@@ -9,6 +9,16 @@
 # Extracted helper methods from run_benchmarks.rb for testing
 module BenchmarkRunner
   class << self
+    def ruby_bench_revision(dir = File.expand_path('..', __dir__))
+      revision = IO.popen(['git', '-C', dir, 'rev-parse', 'HEAD'], err: File::NULL, &:read).strip
+      return 'unknown' unless $?.success? && !revision.empty?
+
+      clean = system('git', '-C', dir, 'diff', '--quiet', 'HEAD', out: File::NULL, err: File::NULL)
+      clean ? revision : "#{revision}-dirty"
+    rescue SystemCallError
+      'unknown'
+    end
+
     # Determine output path - either use the override or find a free file number
     def output_path(out_path_dir, out_override: nil)
       if out_override
@@ -49,14 +59,15 @@ def write_csv(output_path, ruby_descriptions, table)
     end
 
     # Build output text string with metadata, table, and legend
-    def build_output_text(ruby_descriptions, table, format, bench_failures, include_rss: false, include_gc: false, include_pvalue: false, gc_table: nil, gc_format: nil, sections: nil)
+    def build_output_text(ruby_descriptions, table, format, bench_failures, include_rss: false, include_gc: false, include_pvalue: false, gc_table: nil, gc_format: nil, sections: nil, ruby_bench_revision: nil)
       base_name, *other_names = ruby_descriptions.keys
 
       output_str = +""
 
       ruby_descriptions.each do |key, value|
         output_str << "#{key}: #{value}\n"
       end
+      output_str << "ruby-bench: #{ruby_bench_revision}\n" if ruby_bench_revision
 
       output_str << "\n"
       sections ||= [{ table: table, format: format, failures: bench_failures, include_gc: include_gc, gc_table: gc_table, gc_format: gc_format }]

lib/benchmark_runner/cli.rb

@@ -31,6 +31,7 @@ def run
       # Create the output directory
       FileUtils.mkdir_p(args.out_path)
 
+      ruby_bench_revision = BenchmarkRunner.ruby_bench_revision
       ruby_descriptions = {}
 
       suite = BenchmarkSuite.new(
@@ -136,7 +137,7 @@ def run
 
       # Save the output in a text file that we can easily refer to
       output_sections = build_output_sections(ruby_descriptions.keys, bench_data, bench_harnesses, bench_failures)
-      output_str = BenchmarkRunner.build_output_text(ruby_descriptions, table, format, bench_failures, include_rss: args.rss, include_gc: builder.include_gc?, include_pvalue: args.pvalue, gc_table: gc_table, gc_format: gc_format, sections: output_sections)
+      output_str = BenchmarkRunner.build_output_text(ruby_descriptions, table, format, bench_failures, include_rss: args.rss, include_gc: builder.include_gc?, include_pvalue: args.pvalue, gc_table: gc_table, gc_format: gc_format, sections: output_sections, ruby_bench_revision: ruby_bench_revision)
       out_txt_path = output_path + ".txt"
       File.open(out_txt_path, "w") { |f| f.write output_str }
 

test/benchmark_runner_test.rb

@@ -9,6 +9,34 @@
 require 'yaml'
 
 describe BenchmarkRunner do
+  describe '.ruby_bench_revision' do
+    def git(dir, *args)
+      system('git', '-C', dir, '-c', 'user.name=t', '-c', 'user.email=t@t', *args, out: File::NULL, err: File::NULL) or raise "git #{args.join(' ')} failed"
+    end
+
+    it 'returns the HEAD commit, with -dirty only when tracked files change' do
+      Dir.mktmpdir do |dir|
+        git(dir, 'init', '-q')
+        File.write(File.join(dir, 'a.rb'), "1\n")
+        git(dir, 'add', 'a.rb')
+        git(dir, 'commit', '-q', '-m', 'init')
+        head = IO.popen(['git', '-C', dir, 'rev-parse', 'HEAD'], &:read).strip
+
+        File.write(File.join(dir, 'untracked.txt'), "x\n")
+        assert_equal head, BenchmarkRunner.ruby_bench_revision(dir)
+
+        File.write(File.join(dir, 'a.rb'), "2\n")
+        assert_equal "#{head}-dirty", BenchmarkRunner.ruby_bench_revision(dir)
+      end
+    end
+
+    it 'returns unknown outside a git checkout' do
+      Dir.mktmpdir do |dir|
+        assert_equal 'unknown', BenchmarkRunner.ruby_bench_revision(dir)
+      end
+    end
+  end
+
   describe '.check_call' do
     it 'runs a successful command and returns success status' do
       result = nil