[libcxx-commits] [libcxx] [libc++] Make sure `flat_{multi}map::key_compare` handle `boolean-testable` correctly (PR #132621)

[A. Jiang via libcxx-commits]

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@@ -846,7 +846,7 @@ class flat_map {
         __compare_(std::forward<_CompArg>(__comp)...) {}
 
   _LIBCPP_HIDE_FROM_ABI bool __is_sorted_and_unique(auto&& __key_container) const {
-    auto __greater_or_equal_to = [this](const auto& __x, const auto& __y) { return !__compare_(__x, __y); };
+    auto __greater_or_equal_to = [this](const auto& __x, const auto& __y) -> bool { return !__compare_(__x, __y); };
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frederick-vs-ja wrote:

Oh, I see. It's the nature of lambda expression without trailing return type that unfortunately decay-copies the result.

Perhaps there should be some test cases for this, with types in `boolean_testable.h` reused?

https://github.com/llvm/llvm-project/pull/132621