[libcxx-commits] [libcxx] [libc++] Add [[nodiscard]] to std::prev and std::next (PR #109550)

[Louis Dionne via libcxx-commits]

================
@@ -20,7 +20,15 @@ void test() {
   int c_array[] = {1, 2, 3};
   std::initializer_list<int> initializer_list;
 
-  std::empty(container);        // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
-  std::empty(c_array);          // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
-  std::empty(initializer_list); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::empty(container);                                     // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::empty(c_array);                                       // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::empty(initializer_list);                              // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::prev(c_array);                                        // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::next(c_array);                                        // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::prev(c_array);                                // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::prev(container.end(), 2);                     // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::next(container.end(), 2, container.begin());  // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::next(c_array);                                // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::next(container.begin(), 2);                   // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::next(container.end(), 1, container.end());    // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
----------------
ldionne wrote:

```suggestion
#if TEST_STD_VER >= 20
  std::ranges::prev(c_array);                                // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
  std::ranges::prev(container.end(), 2);                     // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
  std::ranges::next(container.end(), 2, container.begin());  // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
  std::ranges::next(c_array);                                // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
  std::ranges::next(container.begin(), 2);                   // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
  std::ranges::next(container.end(), 1, container.end());    // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
#endif
```

And then add `#include "test_macros.h"` above. I think that should fix the CI.

https://github.com/llvm/llvm-project/pull/109550