[llvm] [ADT] Mark reverse and concat as nodiscard (PR #115611)
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Sat Nov 9 08:22:51 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-adt
Author: Jakub Kuderski (kuhar)
<details>
<summary>Changes</summary>
It may not be immediately obvious if these two functions modify the given ranges or return a view over them. We have seen downstream code that mistakenly assumed the given range would be mutated.
Add the `[[nodiscard]]` attribute to prevent these errors. Also clarify the lack of mutation in the documentation comments.
---
Full diff: https://github.com/llvm/llvm-project/pull/115611.diff
1 Files Affected:
- (modified) llvm/include/llvm/ADT/STLExtras.h (+6-3)
``````````diff
diff --git a/llvm/include/llvm/ADT/STLExtras.h b/llvm/include/llvm/ADT/STLExtras.h
index 43c9b80edff78e..4f516ccf4cd6f1 100644
--- a/llvm/include/llvm/ADT/STLExtras.h
+++ b/llvm/include/llvm/ADT/STLExtras.h
@@ -416,7 +416,8 @@ static constexpr bool HasFreeFunctionRBegin =
} // namespace detail
// Returns an iterator_range over the given container which iterates in reverse.
-template <typename ContainerTy> auto reverse(ContainerTy &&C) {
+// Does not mutate the containers.
+template <typename ContainerTy> [[nodiscard]] auto reverse(ContainerTy &&C) {
if constexpr (detail::HasFreeFunctionRBegin<ContainerTy>)
return make_range(adl_rbegin(C), adl_rend(C));
else
@@ -1182,11 +1183,13 @@ template <typename ValueT, typename... RangeTs> class concat_range {
} // end namespace detail
-/// Concatenated range across two or more ranges.
+/// Returns a concatenated range across two or more ranges. Does not modify the
+/// ranges.
///
/// The desired value type must be explicitly specified.
template <typename ValueT, typename... RangeTs>
-detail::concat_range<ValueT, RangeTs...> concat(RangeTs &&... Ranges) {
+[[nodiscard]] detail::concat_range<ValueT, RangeTs...>
+concat(RangeTs &&...Ranges) {
static_assert(sizeof...(RangeTs) > 1,
"Need more than one range to concatenate!");
return detail::concat_range<ValueT, RangeTs...>(
``````````
</details>
https://github.com/llvm/llvm-project/pull/115611
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