[Bug #20647] Disallow `return` directly within a singleton class

parse.y

@@ -318,6 +318,7 @@ struct lex_context {
     unsigned int in_class: 1;
     BITFIELD(enum rb_parser_shareability, shareable_constant_value, 2);
     BITFIELD(enum rescue_context, in_rescue, 2);
+    unsigned int cant_return: 1;
 };
 
 typedef struct RNode_DEF_TEMP rb_node_def_temp_t;
@@ -1696,12 +1697,17 @@ endless_method_name(struct parser_params *p, ID mid, const YYLTYPE *loc)
 #define begin_definition(k, loc_beg, loc_end) \
     do { \
         if (!(p->ctxt.in_class = (k)[0] != 0)) { \
+            /* singleton class */ \
+            p->ctxt.cant_return = !p->ctxt.in_def; \
             p->ctxt.in_def = 0; \
         } \
         else if (p->ctxt.in_def) { \
             YYLTYPE loc = code_loc_gen(loc_beg, loc_end); \
             yyerror1(&loc, k " definition in method body"); \
         } \
+        else { \
+            p->ctxt.cant_return = 1; \
+        } \
         local_push(p, 0); \
     } while (0)
 
@@ -3400,6 +3406,7 @@ def_name	: fname
                         local_push(p, 0);
                         p->ctxt.in_def = 1;
                         p->ctxt.in_rescue = before_rescue;
+                        p->ctxt.cant_return = 0;
                         $$ = $1;
                     }
                 ;
@@ -4628,6 +4635,7 @@ primary		: literal
                     /*% ripper: class!($:cpath, $:superclass, $:bodystmt) %*/
                         local_pop(p);
                         p->ctxt.in_class = $k_class.in_class;
+                        p->ctxt.cant_return = $k_class.cant_return;
                         p->ctxt.shareable_constant_value = $k_class.shareable_constant_value;
                     }
                 | k_class tLSHFT expr_value
@@ -4646,6 +4654,7 @@ primary		: literal
                         local_pop(p);
                         p->ctxt.in_def = $k_class.in_def;
                         p->ctxt.in_class = $k_class.in_class;
+                        p->ctxt.cant_return = $k_class.cant_return;
                         p->ctxt.shareable_constant_value = $k_class.shareable_constant_value;
                     }
                 | k_module cpath
@@ -4662,6 +4671,7 @@ primary		: literal
                     /*% ripper: module!($:cpath, $:bodystmt) %*/
                         local_pop(p);
                         p->ctxt.in_class = $k_module.in_class;
+                        p->ctxt.cant_return = $k_module.cant_return;
                         p->ctxt.shareable_constant_value = $k_module.shareable_constant_value;
                     }
                 | defn_head[head]
@@ -4890,7 +4900,7 @@ k_end		: keyword_end
 
 k_return	: keyword_return
                     {
-                        if (p->ctxt.in_class && !p->ctxt.in_def && !dyna_in_block(p))
+                        if (p->ctxt.cant_return && !dyna_in_block(p))
                             yyerror1(&@1, "Invalid return in class/module body");
                     }
                 ;

prism/prism.c

@@ -15342,6 +15342,7 @@ parse_arguments_list(pm_parser_t *parser, pm_arguments_t *arguments, bool accept
  */
 static void
 parse_return(pm_parser_t *parser, pm_node_t *node) {
+    bool in_sclass = false;
     for (pm_context_node_t *context_node = parser->current_context; context_node != NULL; context_node = context_node->prev) {
         switch (context_node->context) {
             case PM_CONTEXT_BEGIN_ELSE:
@@ -15366,10 +15367,6 @@ parse_return(pm_parser_t *parser, pm_node_t *node) {
             case PM_CONTEXT_PREDICATE:
             case PM_CONTEXT_PREEXE:
             case PM_CONTEXT_RESCUE_MODIFIER:
-            case PM_CONTEXT_SCLASS_ELSE:
-            case PM_CONTEXT_SCLASS_ENSURE:
-            case PM_CONTEXT_SCLASS_RESCUE:
-            case PM_CONTEXT_SCLASS:
             case PM_CONTEXT_TERNARY:
             case PM_CONTEXT_UNLESS:
             case PM_CONTEXT_UNTIL:
@@ -15377,6 +15374,12 @@ parse_return(pm_parser_t *parser, pm_node_t *node) {
                 // Keep iterating up the lists of contexts, because returns can
                 // see through these.
                 continue;
+            case PM_CONTEXT_SCLASS_ELSE:
+            case PM_CONTEXT_SCLASS_ENSURE:
+            case PM_CONTEXT_SCLASS_RESCUE:
+            case PM_CONTEXT_SCLASS:
+                in_sclass = true;
+                continue;
             case PM_CONTEXT_CLASS_ELSE:
             case PM_CONTEXT_CLASS_ENSURE:
             case PM_CONTEXT_CLASS_RESCUE:
@@ -15411,6 +15414,9 @@ parse_return(pm_parser_t *parser, pm_node_t *node) {
                 break;
         }
     }
+    if (in_sclass) {
+        pm_parser_err_node(parser, node, PM_ERR_RETURN_INVALID);
+    }
 }
 
 /**

test/prism/errors/dont_allow_return_inside_sclass_body.txt

@@ -0,0 +1,3 @@
+class << A; return; end
+            ^~~~~~ Invalid return in class/module body
+

test/ruby/test_class.rb

@@ -316,6 +316,7 @@ class TestClass < Test::Unit::TestCase
 
   def test_invalid_return_from_class_definition
     assert_syntax_error("class C; return; end", /Invalid return/)
+    assert_syntax_error("class << Object; return; end", /Invalid return/)
   end
 
   def test_invalid_yield_from_class_definition