[ruby/irb] Reduce internal operations' exposure to benchmarking

(https://github.com/ruby/irb/pull/618)

* Test last value is assigned with measure enabled

* Remove unnecessary `result` variable

`Context#evaluate` always assigns the result of the evaluation to `_` so
we don't need to do it in `Irb#eval_input`.

* Move benchmarking logic into `Context#evaluate`

Current location of the benchmarking logic is too high up and includes
operations like command loading and argument transformation, which should
be excluded. So this commit moves it into `Context#evaluate` to reduce the
noise.

We don't move it further down to `Workspace#evaluate` because `Context`
is an argument of the measure block, which is not available in `Workspace`.

1 files changed, 2 insertions, 18 deletions

diff --git a/lib/irb.rb b/lib/irb.rb
index ed79160b24..64c716fd4c 100644
--- a/lib/irb.rb
+++ b/lib/irb.rb
@@ -558,26 +558,10 @@ module IRB
       @scanner.each_top_level_statement do |line, line_no|
         signal_status(:IN_EVAL) do
           begin
-            if IRB.conf[:MEASURE] && IRB.conf[:MEASURE_CALLBACKS].empty?
-              IRB.set_measure_callback
-            end
             # Assignment expression check should be done before evaluate_line to handle code like `a /2#/ if false; a = 1`
             is_assignment = assignment_expression?(line)
-            if IRB.conf[:MEASURE] && !IRB.conf[:MEASURE_CALLBACKS].empty?
-              result = nil
-              last_proc = proc{ result = evaluate_line(line, line_no) }
-              IRB.conf[:MEASURE_CALLBACKS].inject(last_proc) { |chain, item|
-                _name, callback, arg = item
-                proc {
-                  callback.(@context, line, line_no, arg) do
-                    chain.call
-                  end
-                }
-              }.call
-              @context.set_last_value(result)
-            else
-              evaluate_line(line, line_no)
-            end
+            evaluate_line(line, line_no)
+
             if @context.echo?
               if is_assignment
                 if @context.echo_on_assignment?