[Bug #20033] Dynamic regexp should not assign captures

compile.c

@@ -4213,11 +4213,28 @@ compile_dstr(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node)
 }
 
 static int
-compile_dregx(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node)
+compile_dregx(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, int popped)
 {
     int cnt;
+
+    if (!RNODE_DREGX(node)->nd_next) {
+        VALUE match = RNODE_DREGX(node)->nd_lit;
+        if (RB_TYPE_P(match, T_REGEXP)) {
+            if (!popped) {
+                ADD_INSN1(ret, node, putobject, match);
+                RB_OBJ_WRITTEN(iseq, Qundef, match);
+            }
+            return COMPILE_OK;
+        }
+    }
+
     CHECK(compile_dstr_fragments(iseq, ret, node, &cnt));
     ADD_INSN2(ret, node, toregexp, INT2FIX(RNODE_DREGX(node)->nd_cflag), INT2FIX(cnt));
+
+    if (popped) {
+        ADD_INSN(ret, node, pop);
+    }
+
     return COMPILE_OK;
 }
 
@@ -9901,14 +9918,9 @@ iseq_compile_each0(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const no
       case NODE_EVSTR:
         CHECK(compile_evstr(iseq, ret, RNODE_EVSTR(node)->nd_body, popped));
         break;
-      case NODE_DREGX:{
-        compile_dregx(iseq, ret, node);
-
-        if (popped) {
-            ADD_INSN(ret, node, pop);
-        }
+      case NODE_DREGX:
+        compile_dregx(iseq, ret, node, popped);
         break;
-      }
       case NODE_ONCE:{
         int ic_index = body->ise_size++;
         const rb_iseq_t *block_iseq;

parse.y

@@ -12905,8 +12905,8 @@ new_regexp(struct parser_params *p, NODE *node, int options, const YYLTYPE *loc)
         }
         if (!RNODE_DREGX(node)->nd_next) {
             VALUE src = RNODE_DREGX(node)->nd_lit;
-            nd_set_type(node, NODE_LIT);
-            RB_OBJ_WRITTEN(p->ast, Qnil, RNODE_LIT(node)->nd_lit = reg_compile(p, src, options));
+            VALUE re = reg_compile(p, src, options);
+            RB_OBJ_WRITTEN(p->ast, Qnil, RNODE_DREGX(node)->nd_lit = re);
         }
         if (options & RE_OPTION_ONCE) {
             node = NEW_ONCE(node, loc);

test/ruby/test_parse.rb

@@ -1071,6 +1071,7 @@ x = __ENCODING__
       '(%w();/(?<a>.*)/)',
       '(1; (2; 3; (4; /(?<a>.*)/)))',
       '(1+1; /(?<a>.*)/)',
+      '/#{""}(?<a>.*)/',
     ) do |code, pass|
       token = Random.bytes(4).unpack1("H*")
       if pass