[Bug #21331] Prohibit hash modification during stlike loop

Author: nobu

hash.c

@@ -1404,6 +1404,7 @@ hash_foreach_ensure(VALUE hash)
     return 0;
 }
 
+/* This does not manage iteration level */
 int
 rb_hash_stlike_foreach(VALUE hash, st_foreach_callback_func *func, st_data_t arg)
 {
@@ -1415,6 +1416,7 @@ rb_hash_stlike_foreach(VALUE hash, st_foreach_callback_func *func, st_data_t arg
     }
 }
 
+/* This does not manage iteration level */
 int
 rb_hash_stlike_foreach_with_replace(VALUE hash, st_foreach_check_callback_func *func, st_update_callback_func *replace, st_data_t arg)
 {
@@ -3486,6 +3488,20 @@ transform_values_foreach_replace(st_data_t *key, st_data_t *value, st_data_t arg
     return ST_CONTINUE;
 }
 
+static VALUE
+transform_values_call(VALUE hash)
+{
+    rb_hash_stlike_foreach_with_replace(hash, transform_values_foreach_func, transform_values_foreach_replace, hash);
+    return hash;
+}
+
+static void
+transform_values(VALUE hash)
+{
+    hash_iter_lev_inc(hash);
+    rb_ensure(transform_values_call, hash, hash_foreach_ensure, hash);
+}
+
 /*
  *  call-seq:
  *    transform_values {|value| ... } -> new_hash
@@ -3514,7 +3530,7 @@ rb_hash_transform_values(VALUE hash)
     SET_DEFAULT(result, Qnil);
 
     if (!RHASH_EMPTY_P(hash)) {
-        rb_hash_stlike_foreach_with_replace(result, transform_values_foreach_func, transform_values_foreach_replace, result);
+        transform_values(result);
         compact_after_delete(result);
     }
 
@@ -3549,7 +3565,7 @@ rb_hash_transform_values_bang(VALUE hash)
     rb_hash_modify_check(hash);
 
     if (!RHASH_TABLE_EMPTY_P(hash)) {
-        rb_hash_stlike_foreach_with_replace(hash, transform_values_foreach_func, transform_values_foreach_replace, hash);
+        transform_values(hash);
     }
 
     return hash;

test/ruby/test_hash.rb

@@ -1853,6 +1853,14 @@ def test_transform_values_bang
       end
     end
     assert_equal(@cls[a: 2, b: 2, c: 3, d: 4, e: 5, f: 6, g: 7, h: 8, i: 9, j: 10], x)
+
+    x = (1..1337).to_h {|k| [k, k]}
+    assert_raise_with_message(RuntimeError, /rehash during iteration/) do
+      x.transform_values! {|v|
+        x.rehash if v == 1337
+        v * 2
+      }
+    end
   end
 
   def hrec h, n, &b