[libcxx-commits] [libcxx] [libc++] Eliminate extra allocations from `std::move(oss).str()` (PR #67294)

[via libcxx-commits]

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+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// TODO: Change to XFAIL once https://github.com/llvm/llvm-project/issues/40340 is fixed
+// UNSUPPORTED: availability-pmr-missing
+
+// This test ensures that we properly propagate allocators from istringstream's
+// inner string object to the new string returned from .str().
+// `str() const&` is specified to preserve the allocator (not copy the string).
+// `str() &&` isn't specified, but should preserve the allocator (move the string).
+
+#include <cassert>
+#include <memory>
+#include <memory_resource>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <type_traits>
+
+#include "make_string.h"
+#include "test_macros.h"
+
+template <class T>
+struct SocccAllocator {
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philnik777 wrote:

I think it would make sense to move this to support/allocators.h`.

https://github.com/llvm/llvm-project/pull/67294