gcc/testsuite/gcc.dg/c23-tag-enum-3.c - gcc - Git at Google

 /* { dg-do compile }
  * { dg-options "-std=c23" }
  */

 enum A { N = 0 * sizeof(enum A { M = 1 }) }; 	/* { dg-error "nested" } */
	/* { dg-do compile }
	* { dg-options "-std=c23" }
	*/

	enum A { N = 0 * sizeof(enum A { M = 1 }) }; /* { dg-error "nested" } */