clang/test/Sema/c2x-nodiscard.c

   1 // RUN: %clang_cc1 -fsyntax-only -std=c2x -verify %s
   2
   3 // This is the latest version of nodiscard that we support.
   4 _Static_assert(__has_c_attribute(nodiscard) == 202003L);
   5
   6 struct [[nodiscard]] S1 { // ok
   7   int i;
   8 };
   9 struct [[nodiscard, nodiscard]] S2 { // ok
  10   int i;
  11 };
  12 struct [[nodiscard("Wrong")]] S3 {
  13   int i;
  14 };
  15
  16 struct S3 get_s3(void);
  17
  18 [[nodiscard]] int f1(void);
  19 enum [[nodiscard]] E1 { One };
  20
  21 [[nodiscard]] int i; // expected-warning {{'nodiscard' attribute only applies to Objective-C methods, enums, structs, unions, classes, functions, function pointers, and typedefs}}
  22
  23 struct [[nodiscard]] S4 {
  24   int i;
  25 };
  26 struct S4 get_s(void);
  27
  28 enum [[nodiscard]] E2 { Two };
  29 enum E2 get_e(void);
  30
  31 [[nodiscard]] int get_i(void);
  32
  33 void f2(void) {
  34   get_s(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
  35   get_s3(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute: Wrong}}
  36   get_i(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
  37   get_e(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
  38
  39   // Okay, warnings are not encouraged
  40   (void)get_s();
  41   (void)get_s3();
  42   (void)get_i();
  43   (void)get_e();
  44 }
  45
  46 struct [[nodiscard]] error_info{
  47   int i;
  48 };
  49
  50 struct error_info enable_missile_safety_mode(void);
  51 void launch_missiles(void);
  52 void test_missiles(void) {
  53   enable_missile_safety_mode(); // expected-warning {{ignoring return value of function declared with 'nodiscard'}}
  54   launch_missiles();
  55 }
  56