Support eval "return" at toplevel

Since Ruby 2.4, `return` is supported at toplevel.  This makes `eval "return"`
also supported at toplevel.

This mostly uses the same tests as direct `return` at toplevel, with a couple
differences:

`END {return if false}` is a SyntaxError, but `END {eval "return" if false}`
is not an error since the eval is never executed. `END {return}` is a
SyntaxError, but `END {eval "return"}` is a LocalJumpError.

The following is a SyntaxError:

```ruby
class X
nil&defined?0--begin e=no_method_error(); return; 0;end
end
```

However, the following is not, because the eval is never executed:

```ruby
class X
nil&defined?0--begin e=no_method_error(); eval "return"; 0;end
end
```

Fixes [Bug #19779]

1 files changed, 10 insertions, 1 deletions

diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 8e1ac27c51..50ca9902fd 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -1809,7 +1809,16 @@ vm_throw_start(const rb_execution_context_t *ec, rb_control_frame_t *const reg_c
                             }
                         }
                         break;
-                      case ISEQ_TYPE_EVAL:
+                      case ISEQ_TYPE_EVAL: {
+                        const rb_iseq_t *is = escape_cfp->iseq;
+                        enum rb_iseq_type t = ISEQ_BODY(is)->type;
+                        while (t == ISEQ_TYPE_RESCUE || t == ISEQ_TYPE_ENSURE || t == ISEQ_TYPE_EVAL) {
+                            if (!(is = ISEQ_BODY(is)->parent_iseq)) break;
+                            t = ISEQ_BODY(is)->type;
+                        }
+                        toplevel = t == ISEQ_TYPE_TOP || t == ISEQ_TYPE_MAIN;
+                        break;
+                      }
                       case ISEQ_TYPE_CLASS:
                         toplevel = 0;
                         break;