[libcxx-commits] [libcxx] [libc++][ranges] Applied `[[nodiscard]]` to `views::zip_transform` (PR #207120)

[A. Jiang via libcxx-commits]

================
@@ -0,0 +1,88 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++23
+
+// Check that functions are marked [[nodiscard]]
+
+#include <ranges>
+#include <utility>
+#include <vector>
+
+struct View : std::ranges::view_interface<View> {
+  int* begin();
+  const int* begin() const;
+  volatile int* end();
+  const volatile int* end() const;
+
+  int size() const;
+};
+static_assert(!std::ranges::common_range<View>);
+static_assert(!std::same_as<std::ranges::iterator_t<View>, std::ranges::iterator_t<const View>>);
+static_assert(!std::same_as<std::ranges::sentinel_t<View>, std::ranges::sentinel_t<const View>>);
+
+template <class... Args>
+struct Invocable {
+  int operator()(Args...) const { return 5; }
+};
+
+void test() {
+  View range;
+  std::ranges::zip_transform_view ztv{[](int x) { return x; }, range};
+
+  // [range.zip_transform.view]
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  ztv.begin();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::as_const(ztv).begin();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  ztv.end();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::as_const(ztv).end();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  ztv.size();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::as_const(ztv).size();
+
+  // [range.zip_transform.iterator]
+
+  auto it  = ztv.begin();
+  auto cIt = std::as_const(ztv).begin();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  *cIt;
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  cIt[0];
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  it + 1;
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  1 + it;
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  it - 1;
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  it - it;
+
+  // [range.zip_transform.sentinel]
+
+  auto st = ztv.end();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  it - st;
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  st - it;
+
+  // [range.zip_transform.overview]
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::views::zip_transform(Invocable<>{});
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::views::zip_transform([](int x) { return x; }, range);
+}
----------------
frederick-vs-ja wrote:

Let's add the conventional empty ending line. Also, I think this PR is almost ready and there's no related test failure.

https://github.com/llvm/llvm-project/pull/207120