Treat return in block in class/module as LocalJumpError (#2511)

return directly in class/module is an error, so return in
proc in class/module should also be an error.  I believe the
previous behavior was an unintentional oversight during the
addition of top-level return in 2.4.

spec/ruby/language/return_spec.rb

@@ -443,17 +443,18 @@ describe "The return keyword" do
       end
 
       describe "within a block within a class" do
-        it "is allowed" do
-          File.write(@filename, <<-END_OF_CODE)
-            class ReturnSpecs::A
-              ScratchPad << "before return"
-              1.times { return }
-              ScratchPad << "after return"
-            end
-          END_OF_CODE
+        ruby_version_is "2.7" do
+          it "is not allowed" do
+            File.write(@filename, <<-END_OF_CODE)
+              class ReturnSpecs::A
+                ScratchPad << "before return"
+                1.times { return }
+                ScratchPad << "after return"
+              end
+            END_OF_CODE
 
-          load @filename
-          ScratchPad.recorded.should == ["before return"]
+            -> { load @filename }.should raise_error(LocalJumpError)
+          end
         end
       end
 

test/ruby/test_syntax.rb

@@ -1272,6 +1272,10 @@ eom
     assert_warn(/argument of top-level return is ignored/) {eval("return 1")}
   end
 
+  def test_return_in_proc_in_class
+    assert_in_out_err(['-e', 'class TestSyntax; proc{ return }.call; end'], "", [], /^-e:1:.*unexpected return \(LocalJumpError\)/)
+  end
+
   def test_syntax_error_in_rescue
     bug12613 = '[ruby-core:76531] [Bug #12613]'
     assert_syntax_error("#{<<-"begin;"}\n#{<<-"end;"}", /Invalid retry/, bug12613)

vm_insnhelper.c

@@ -1258,7 +1258,10 @@ vm_throw_start(const rb_execution_context_t *ec, rb_control_frame_t *const reg_c
 		    switch (escape_cfp->iseq->body->type) {
 		      case ISEQ_TYPE_TOP:
 		      case ISEQ_TYPE_MAIN:
-			if (toplevel) goto valid_return;
+                        if (toplevel) {
+                            if (in_class_frame) goto unexpected_return;
+                            goto valid_return;
+                        }
 			break;
 		      case ISEQ_TYPE_EVAL:
 		      case ISEQ_TYPE_CLASS:
@@ -1276,6 +1279,7 @@ vm_throw_start(const rb_execution_context_t *ec, rb_control_frame_t *const reg_c
 
 	    escape_cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(escape_cfp);
 	}
+      unexpected_return:;
 	rb_vm_localjump_error("unexpected return", throwobj, TAG_RETURN);
 
       valid_return:;