[libcxx-commits] [libcxx] [libc++][ranges] Applied `[[nodiscard]]` to `split_view` (PR #205161)

[via libcxx-commits]

llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Hristo Hristov (H-G-Hristov)

<details>
<summary>Changes</summary>

Towards #<!-- -->172124

# References:

- https://wg21.link/range.split
- https://libcxx.llvm.org/CodingGuidelines.html#apply-nodiscard-where-relevant

---
Full diff: https://github.com/llvm/llvm-project/pull/205161.diff


2 Files Affected:

- (modified) libcxx/include/__ranges/split_view.h (+6-6) 
- (added) libcxx/test/libcxx/ranges/range.adaptors/range.split/nodiscard.verify.cpp (+53) 


``````````diff
diff --git a/libcxx/include/__ranges/split_view.h b/libcxx/include/__ranges/split_view.h
index 2ec908ba4070e..2e476691d353f 100644
--- a/libcxx/include/__ranges/split_view.h
+++ b/libcxx/include/__ranges/split_view.h
@@ -88,22 +88,22 @@ class split_view : public view_interface<split_view<_View, _Pattern>> {
   split_view(_Range&& __range, range_value_t<_Range> __elem)
       : __base_(views::all(std::forward<_Range>(__range))), __pattern_(views::single(std::move(__elem))) {}
 
-  _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
     requires copy_constructible<_View>
   {
     return __base_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr __iterator begin() {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __iterator begin() {
     if (!__cached_begin_.__has_value()) {
       __cached_begin_.__emplace(__find_next(ranges::begin(__base_)));
     }
     return {*this, ranges::begin(__base_), *__cached_begin_};
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr auto end() {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end() {
     if constexpr (common_range<_View>) {
       return __iterator{*this, ranges::end(__base_), {}};
     } else {
@@ -142,9 +142,9 @@ struct split_view<_View, _Pattern>::__iterator {
       split_view<_View, _Pattern>& __parent, iterator_t<_View> __current, subrange<iterator_t<_View>> __next)
       : __parent_(std::addressof(__parent)), __cur_(std::move(__current)), __next_(std::move(__next)) {}
 
-  _LIBCPP_HIDE_FROM_ABI constexpr iterator_t<_View> base() const { return __cur_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr iterator_t<_View> base() const { return __cur_; }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr value_type operator*() const { return {__cur_, __next_.begin()}; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr value_type operator*() const { return {__cur_, __next_.begin()}; }
 
   _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator++() {
     __cur_ = __next_.begin();
diff --git a/libcxx/test/libcxx/ranges/range.adaptors/range.split/nodiscard.verify.cpp b/libcxx/test/libcxx/ranges/range.adaptors/range.split/nodiscard.verify.cpp
new file mode 100644
index 0000000000000..213d88c834a53
--- /dev/null
+++ b/libcxx/test/libcxx/ranges/range.adaptors/range.split/nodiscard.verify.cpp
@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++20
+
+// Check that functions are marked [[nodiscard]]
+
+#include <string>
+#include <ranges>
+#include <utility>
+
+void test() {
+  std::string range{"19,28,29,49,82,94"};
+  char pattern = ',';
+
+  auto v = std::views::split(range, pattern);
+
+  // [range.split.view]
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  v.base();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::move(v).base();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  v.begin();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  v.end();
+
+  // [range.split.iterator]
+
+  auto it = v.begin();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::as_const(it).base();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  *std::as_const(it);
+
+  // [range.split.overview]
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::views::split(range, pattern);
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::views::split(pattern);
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/205161