llvm-project/clang/test/Parser/struct-recursion.c

// RUN: %clang_cc1 %s -fsyntax-only

// C99 6.7.2.3p11

// mutually recursive structs
struct s1 { struct s2 *A; };
struct s2 { struct s1 *B; };

// both types are complete now.
struct s1 a;
struct s2 b;