[ruby/benchmark] Adjust ljust Benchmark#bm with labels was not using the highest length among the labels to adjust the correct ljust. Instead of printing the result during the report generation, now it is waiting to print the result once it is generated.

Benchmark.bm { |x|
  x.item("aaaa") { 1 }
  x.item("aaaaaaaa") { 0 }
}

After

              user     system      total        real
aaaa      0.000005   0.000002   0.000007 (  0.000003)
aaaaaaaa  0.000001   0.000001   0.000002 (  0.000002)

Before

       user     system      total        real
aaaa  0.000005   0.000001   0.000006 (  0.000003)
aaaaaaaa  0.000002   0.000001   0.000003 (  0.000003)

https://github.com/ruby/benchmark/commit/3e74533ead

2 files changed, 12 insertions, 6 deletions

diff --git a/lib/benchmark.rb b/lib/benchmark.rb
index 5072bdc2f3..6fdc26c482 100644
--- a/lib/benchmark.rb
+++ b/lib/benchmark.rb
@@ -173,9 +173,15 @@ module Benchmark
     label_width ||= 0
     label_width += 1
     format ||= FORMAT
-    print ' '*label_width + caption unless caption.empty?
     report = Report.new(label_width, format)
     results = yield(report)
+
+    print " " * report.width + caption unless caption.empty?
+    report.list.each { |i|
+      print i.label.to_s.ljust(report.width)
+      print i.format(report.format, *format)
+    }
+
     Array === results and results.grep(Tms).each {|t|
       print((labels.shift || t.label || "").ljust(label_width), t.format(format))
     }
@@ -380,16 +386,16 @@ module Benchmark
     # formatting rules.
     #
     def item(label = "", *format, &blk) # :yield:
-      print label.to_s.ljust(@width)
+      w = label.to_s.length
+      @width = w if @width < w
       @list << res = Benchmark.measure(label, &blk)
-      print res.format(@format, *format)
       res
     end
 
     alias report item
 
     # An array of Benchmark::Tms objects representing each item.
-    attr_reader :list
+    attr_reader :width, :format, :list
   end
 
 
diff --git a/test/benchmark/test_benchmark.rb b/test/benchmark/test_benchmark.rb
index ddd4a591bb..2e0c47af75 100644
--- a/test/benchmark/test_benchmark.rb
+++ b/test/benchmark/test_benchmark.rb
@@ -65,9 +65,9 @@ BENCH
 
   def test_benchmark_does_not_print_any_space_if_the_given_caption_is_empty
     assert_equal(<<-BENCH, capture_bench_output(:benchmark))
-first  --time--   --time--   --time-- (  --time--)
+first   --time--   --time--   --time-- (  --time--)
 second  --time--   --time--   --time-- (  --time--)
-third  --time--   --time--   --time-- (  --time--)
+third   --time--   --time--   --time-- (  --time--)
 BENCH
   end