irb.rb: restore the last error

* lib/irb.rb (eval_input): restore the last error `$!`, as the
  previous result.  [Feature #14684]

* lib/irb/context.rb (evaluate): add `exception` keyword argument
  to set the last error.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63150 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/irb.rb

@@ -439,6 +439,8 @@ module IRB
 
     # Evaluates input for this session.
     def eval_input
+      last_error = nil
+
       @scanner.set_prompt do
         |ltype, indent, continue, line_no|
         if ltype
@@ -488,7 +490,7 @@ module IRB
         signal_status(:IN_EVAL) do
           begin
             line.untaint
-            @context.evaluate(line, line_no)
+            @context.evaluate(line, line_no, exception: last_error)
             output_value if @context.echo?
             exc = nil
           rescue Interrupt => exc
@@ -497,6 +499,7 @@ module IRB
           rescue Exception => exc
           end
           if exc
+            last_error = exc
             handle_exception(exc)
           end
         end

lib/irb/context.rb

@@ -376,8 +376,12 @@ module IRB
       @debug_level > 0
     end
 
-    def evaluate(line, line_no) # :nodoc:
+    def evaluate(line, line_no, exception: nil) # :nodoc:
       @line_no = line_no
+      if exception
+        line = "begin ::Kernel.raise _; rescue _.class; #{line}; end"
+        @workspace.local_variable_set(:_, exception)
+      end
       set_last_value(@workspace.evaluate(self, line, irb_path, line_no))
     end
 

test/irb/test_context.rb

@@ -40,5 +40,14 @@ module TestIRB
       assert_same(obj, @context.last_value)
       assert_same(obj, @context.evaluate('_', 1))
     end
+
+    def test_evaluate_with_exception
+      assert_nil(@context.evaluate("$!", 1))
+      e = assert_raise_with_message(RuntimeError, 'foo') {
+        @context.evaluate("raise 'foo'", 1)
+      }
+      assert_equal('foo', e.message)
+      assert_same(e, @context.evaluate('$!', 1, exception: e))
+    end
   end
 end