These are valid init patterns that chibicc rejects.
int fn(void) {
union U { struct {char a,b;}; };
// trailing comma in initializer list
union U u0 = {.a = 4,};
// multiple initializers for inner struct member
union U u1 = {.a = 7, 8};
union U u2 = {.b = 4, .a = 3};
// direct assignment
union U u3;
union U u4 = u3;
}
These are valid init patterns that chibicc rejects.