Implement Debugger Locals (_raised_ and _returned_)

lib/debug/thread_client.rb

@@ -340,10 +340,20 @@ def instance_eval_for_cmethod frame_self, src
       frame_self.instance_eval(src)
     end
 
+    SPECIAL_LOCALS = [
+      [:raised_exception, "_raised_"],
+      [:return_value, "_returned_"],
+    ]
+
     def frame_eval src, re_raise: false
       @success_last_eval = false
 
       b = current_frame&.eval_binding || TOPLEVEL_BINDING
+      b = b.dup
+
+      SPECIAL_LOCALS.each do |m, local_name|
+        b.local_variable_set(local_name, current_frame.send(m))
+      end
 
       result = if b
                   f, _l = b.source_location

test/debug/debugger_local_test.rb

@@ -0,0 +1,89 @@
+# frozen_string_literal: truk
+
+require_relative '../support/test_case'
+
+module DEBUGGER__
+  class DebuggerLocalsTest < TestCase
+    class RaisedTest < TestCase
+      def program
+        <<~RUBY
+     1| _rescued_ = 1111
+     2| foo rescue nil
+     3|
+     4| # check repl variable doesn't leak to the program
+     5| result = _rescued_ * 2
+     6| binding.b
+        RUBY
+      end
+
+      def test_raised_is_accessible_from_repl
+        debug_code(program) do
+          type "catch Exception"
+          type "c"
+          type "_raised_"
+          assert_line_text(/#<NameError: undefined local variable or method `foo' for main:Object/)
+          type "c"
+          type "result"
+          assert_line_text(/2222/)
+          type "c"
+        end
+      end
+
+      def test_raised_is_accessible_from_command
+        debug_code(program) do
+          type "catch Exception pre: p _raised_"
+          type "c"
+          assert_line_text(/#<NameError: undefined local variable or method `foo' for main:Object/)
+          type "c"
+          type "result"
+          assert_line_text(/2222/)
+          type "c"
+        end
+      end
+    end
+
+    class ReturnedTest < TestCase
+      def program
+        <<~RUBY
+   1| _returned_ = 1111
+   2|
+   3| def foo
+   4|   "foo"
+   5| end
+   6|
+   7| foo
+   8|
+   9| # check repl variable doesn't leak to the program
+  10| result = _returned_ * 2
+  11|
+  12| binding.b
+        RUBY
+      end
+
+      def test_returned_is_accessible_from_repl
+        debug_code(program) do
+          type "b 5"
+          type "c"
+          type "_returned_ + 'bar'"
+          assert_line_text(/"foobar"/)
+          type "c"
+          type "result"
+          assert_line_text(/2222/)
+          type "q!"
+        end
+      end
+
+      def test_returned_is_accessible_from_command
+        debug_code(program) do
+          type "b 5 pre: p _returned_ + 'bar'"
+          type "c"
+          assert_line_text(/"foobar"/)
+          type "c"
+          type "result"
+          assert_line_text(/2222/)
+          type "q!"
+        end
+      end
+    end
+  end
+end