Pass statements to Context#evaluate

This has a few benefits:

- We can keep hiding the evaluation logic inside the Context level, which
  has always been the convention until #824 was merged recently.
- Although not an official API, gems like `debug` and `mission_control-jobs`
  patch `Context#evaluate` to wrap their own logic around it. This implicit
  contract was broken after #824, and this change restores it.

In addition to the refactor, I also converted some context-level evaluation
tests into integration tests, which are more robust and easier to maintain.

lib/irb.rb

@@ -1028,21 +1028,7 @@ def eval_input
               return statement.code
             end
 
-            case statement
-            when Statement::EmptyInput
-              # Do nothing
-            when Statement::Expression
-              @context.evaluate(statement.code, line_no)
-            when Statement::Command
-              ret = statement.command_class.execute(@context, statement.arg)
-              # TODO: Remove this output once we have a better way to handle it
-              # This is to notify `debug`'s test framework that the current input has been processed
-              # We also need to have a way to restart/stop threads around command execution
-              # when being used as `debug`'s console.
-              # https://github.com/ruby/debug/blob/master/lib/debug/irb_integration.rb#L8-L13
-              puts "INTERNAL_INFO: {}" if @context.with_debugger && ENV['RUBY_DEBUG_TEST_UI'] == 'terminal'
-              @context.set_last_value(ret)
-            end
+            @context.evaluate(statement, line_no)
 
             if @context.echo? && !statement.suppresses_echo?
               if statement.is_assignment?

lib/irb/context.rb

@@ -585,31 +585,44 @@ def inspect_mode=(opt)
       @inspect_mode
     end
 
-    def evaluate(line, line_no) # :nodoc:
+    def evaluate(statement, line_no) # :nodoc:
       @line_no = line_no
       result = nil
 
+      case statement
+      when Statement::EmptyInput
+        return
+      when Statement::Expression
+        result = evaluate_expression(statement.code, line_no)
+      when Statement::Command
+        result = statement.command_class.execute(self, statement.arg)
+      end
+
+      set_last_value(result)
+    end
+
+    def evaluate_expression(code, line_no) # :nodoc:
+      result = nil
       if IRB.conf[:MEASURE] && IRB.conf[:MEASURE_CALLBACKS].empty?
         IRB.set_measure_callback
       end
 
       if IRB.conf[:MEASURE] && !IRB.conf[:MEASURE_CALLBACKS].empty?
         last_proc = proc do
-          result = workspace.evaluate(line, @eval_path, line_no)
+          result = workspace.evaluate(code, @eval_path, line_no)
         end
         IRB.conf[:MEASURE_CALLBACKS].inject(last_proc) do |chain, item|
           _name, callback, arg = item
           proc do
-            callback.(self, line, line_no, arg) do
+            callback.(self, code, line_no, arg) do
               chain.call
             end
           end
         end.call
       else
-        result = workspace.evaluate(line, @eval_path, line_no)
+        result = workspace.evaluate(code, @eval_path, line_no)
       end
-
-      set_last_value(result)
+      result
     end
 
     def inspect_last_value # :nodoc:

test/irb/test_context.rb

@@ -28,35 +28,6 @@ def teardown
       restore_encodings
     end
 
-    def test_last_value
-      assert_nil(@context.last_value)
-      assert_nil(@context.evaluate('_', 1))
-      obj = Object.new
-      @context.set_last_value(obj)
-      assert_same(obj, @context.last_value)
-      assert_same(obj, @context.evaluate('_', 1))
-    end
-
-    def test_evaluate_with_encoding_error_without_lineno
-      if RUBY_ENGINE == 'truffleruby'
-        omit "Remove me after https://github.com/ruby/prism/issues/2129 is addressed and adopted in TruffleRuby"
-      end
-
-      if RUBY_VERSION >= "3.4."
-        omit "Now raises SyntaxError"
-      end
-
-      assert_raise_with_message(EncodingError, /invalid symbol/) {
-        @context.evaluate(%q[:"\xAE"], 1)
-        # The backtrace of this invalid encoding hash doesn't contain lineno.
-      }
-    end
-
-    def test_evaluate_still_emits_warning
-      assert_warning("(irb):1: warning: END in method; use at_exit\n") do
-        @context.evaluate(%q[def foo; END {}; end], 1)
-      end
-    end
 
     def test_eval_input
       verbose, $VERBOSE = $VERBOSE, nil
@@ -382,7 +353,7 @@ def test_omit_multiline_on_assignment
         end
         assert_empty err
         assert_equal("=> \n#{value}\n", out)
-        irb.context.evaluate('A.remove_method(:inspect)', 0)
+        irb.context.evaluate_expression('A.remove_method(:inspect)', 0)
 
         input.reset
         irb.context.echo = true
@@ -392,7 +363,7 @@ def test_omit_multiline_on_assignment
         end
         assert_empty err
         assert_equal("=> #{value_first_line[0..(input.winsize.last - 9)]}...\n=> \n#{value}\n", out)
-        irb.context.evaluate('A.remove_method(:inspect)', 0)
+        irb.context.evaluate_expression('A.remove_method(:inspect)', 0)
 
         input.reset
         irb.context.echo = true
@@ -402,7 +373,7 @@ def test_omit_multiline_on_assignment
         end
         assert_empty err
         assert_equal("=> \n#{value}\n=> \n#{value}\n", out)
-        irb.context.evaluate('A.remove_method(:inspect)', 0)
+        irb.context.evaluate_expression('A.remove_method(:inspect)', 0)
 
         input.reset
         irb.context.echo = false
@@ -412,7 +383,7 @@ def test_omit_multiline_on_assignment
         end
         assert_empty err
         assert_equal("", out)
-        irb.context.evaluate('A.remove_method(:inspect)', 0)
+        irb.context.evaluate_expression('A.remove_method(:inspect)', 0)
 
         input.reset
         irb.context.echo = false
@@ -422,7 +393,7 @@ def test_omit_multiline_on_assignment
         end
         assert_empty err
         assert_equal("", out)
-        irb.context.evaluate('A.remove_method(:inspect)', 0)
+        irb.context.evaluate_expression('A.remove_method(:inspect)', 0)
 
         input.reset
         irb.context.echo = false
@@ -432,7 +403,7 @@ def test_omit_multiline_on_assignment
         end
         assert_empty err
         assert_equal("", out)
-        irb.context.evaluate('A.remove_method(:inspect)', 0)
+        irb.context.evaluate_expression('A.remove_method(:inspect)', 0)
       end
     end
 

test/irb/test_irb.rb

@@ -42,6 +42,56 @@ class Foo
       assert_include output, "From: #{@ruby_file.path}:1"
     end
 
+    def test_underscore_stores_last_result
+      write_ruby <<~'RUBY'
+        binding.irb
+      RUBY
+
+      output = run_ruby_file do
+        type "1 + 1"
+        type "_ + 10"
+        type "exit!"
+      end
+
+      assert_include output, "=> 12"
+    end
+
+    def test_evaluate_with_encoding_error_without_lineno
+      if RUBY_ENGINE == 'truffleruby'
+        omit "Remove me after https://github.com/ruby/prism/issues/2129 is addressed and adopted in TruffleRuby"
+      end
+
+      if RUBY_VERSION >= "3.4."
+        omit "Now raises SyntaxError"
+      end
+
+      write_ruby <<~'RUBY'
+        binding.irb
+      RUBY
+
+      output = run_ruby_file do
+        type %q[:"\xAE"]
+        type "exit!"
+      end
+
+      assert_include output, 'invalid symbol in encoding UTF-8 :"\xAE"'
+      # EncodingError would be wrapped with ANSI escape sequences, so we assert it separately
+      assert_include output, "EncodingError"
+    end
+
+    def test_evaluate_still_emits_warning
+      write_ruby <<~'RUBY'
+        binding.irb
+      RUBY
+
+      output = run_ruby_file do
+        type %q[def foo; END {}; end]
+        type "exit!"
+      end
+
+      assert_include output, '(irb):1: warning: END in method; use at_exit'
+    end
+
     def test_symbol_aliases_dont_affect_ruby_syntax
       write_ruby <<~'RUBY'
         $foo = "It's a foo"