Decay a function to a pointer in the func param context

parse.c

@@ -569,12 +569,18 @@ static Type *func_params(Token **rest, Token *tok, Type *ty) {
     Type *ty2 = declspec(&tok, tok, NULL);
     ty2 = declarator(&tok, tok, ty2);
 
-    // "array of T" is converted to "pointer to T" only in the parameter
-    // context. For example, *argv[] is converted to **argv by this.
+    Token *name = ty2->name;
+
     if (ty2->kind == TY_ARRAY) {
-      Token *name = ty2->name;
+      // "array of T" is converted to "pointer to T" only in the parameter
+      // context. For example, *argv[] is converted to **argv by this.
       ty2 = pointer_to(ty2->base);
       ty2->name = name;
+    } else if (ty2->kind == TY_FUNC) {
+      // Likewise, a function is converted to a pointer to a function
+      // only in the parameter context.
+      ty2 = pointer_to(ty2);
+      ty2->name = name;
     }
 
     cur = cur->next = copy_type(ty2);

test/function.c

@@ -112,6 +112,8 @@ int (*fnptr(int (*fn)(int n, ...)))(int, ...) {
   return fn;
 }
 
+int param_decay2(int x()) { return x(); }
+
 int main() {
   ASSERT(3, ret3());
   ASSERT(8, add2(3, 5));
@@ -187,6 +189,8 @@ int main() {
   ASSERT(7, ({ int (*fn)(int,int) = add2; fn(2,5); }));
   ASSERT(6, fnptr(add_all)(3, 1, 2, 3));
 
+  ASSERT(3, param_decay2(ret3));
+
   printf("OK\n");
   return 0;
 }