typedef struct t t; みたいな宣言の意味; 同じデータ構造なんだけど、名前を変えて取り違えたときに警告を出すため

voidtype.c

#include <stdlib.h>
#include <stdbool.h>
#include <stdio.h>

#define dfunc(f) ((void (void *)) f)            \

typedef struct set_t {
  int cap;
  int num;
  void ** t;
} set;

set * SET_new (int n)
{
  set * t = malloc(sizeof(set));
  void * x = malloc(sizeof(void *) * n);
  t->cap = n;
  t->num = 0;
  t->t = x;
  return t;
}

bool SET_find (void * e, set * s){
  for (int i = 0; i < s->num; i++)
    {
      if (s->t[i] == e)
        return true;
    }
  return false;
}

void SET_add (void * e, set * s){
  if (s->cap > s->num) {
    s->t = realloc (s->t, s->cap * 2);
    s->cap = s->cap * 2;
  }
  s->t[s->num] = e;
  s->num += 1;
}

void dump (set * s, void f (void *)) {
  for (int i = 0; i < s->num; i++)
    f (s->t[i]);
}

void print_int (int * n){
  printf("%d\n",  * n);
}

int * Int_new(int n) {
  int * c = malloc(sizeof(int));
  *c = n;
  return c;
}

typedef struct intset intset;

intset * INTSET_new(int n) {
  return (intset *) SET_new(n);
}

void INTSET_add (int n, intset * s) {
  int * c = malloc(sizeof(int));
  *c = n;
  SET_add (c, (set *)s);
}

int main()
{
  // 警告が出ない
  intset * s = INTSET_new(1);
  INTSET_add(1, s);
  INTSET_add(2, s);
  INTSET_add(3, s);
  INTSET_add(4, s);

  // 警告が出る
  // a.c: In function ‘main’:
  // a.c:78:13: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
  // set * t = INTSET_new(1);
  //       ^
  set * t = INTSET_new(1);
}