[libcxx-commits] [libcxx] [libc++][strings] P2591R5: Concatenation of strings and string views (PR #88389)

[Giuseppe D'Angelo 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, c++20, c++23
+
+// <string>
+
+// [string.op.plus]
+//
+// template<class charT, class traits, class Allocator>
+//   constexpr basic_string<charT, traits, Allocator>
+//     operator+(const basic_string<charT, traits, Allocator>& lhs,
+//               type_identity_t<basic_string_view<charT, traits>> rhs);                           // Since C++26
+// template<class charT, class traits, class Allocator>
+//   constexpr basic_string<charT, traits, Allocator>
+//     operator+(basic_string<charT, traits, Allocator>&& lhs,
+//               type_identity_t<basic_string_view<charT, traits>> rhs);                           // Since C++26
+// template<class charT, class traits, class Allocator>
+//   constexpr basic_string<charT, traits, Allocator>
+//     operator+(type_identity_t<basic_string_view<charT, traits>> lhs,
+//               const basic_string<charT, traits, Allocator>& rhs);                               // Since C++26
+// template<class charT, class traits, class Allocator>
+//   constexpr basic_string<charT, traits, Allocator>
+//     operator+(type_identity_t<basic_string_view<charT, traits>> lhs,
+//               basic_string<charT, traits, Allocator>&& rhs);                                    // Since C++26
+
+#include <cassert>
+#include <concepts>
+#include <string>
+#include <utility>
+
+#include "asan_testing.h"
+#include "constexpr_char_traits.h"
+#include "make_string.h"
+#include "min_allocator.h"
+#include "test_allocator.h"
+#include "test_macros.h"
+
+#define CS(S) MAKE_CSTRING(CharT, S)
+#define ST(S, a) std::basic_string<CharT, TraitsT, AllocT>(MAKE_CSTRING(CharT, S), MKSTR_LEN(CharT, S), a)
+#define SV(S) std::basic_string_view<CharT, TraitsT>(MAKE_CSTRING(CharT, S), MKSTR_LEN(CharT, S))
+
+template <typename CharT, typename TraitsT, typename AllocT>
+constexpr void test(const CharT* x, const CharT* y, const CharT* expected) {
+  AllocT allocator;
+
+  // string& + string_view
+  {
+    std::basic_string<CharT, TraitsT, AllocT> st{x, allocator};
+    std::basic_string_view<CharT, TraitsT> sv{y};
+
+    std::same_as<std::basic_string<CharT, TraitsT, AllocT>> decltype(auto) result = st + sv;
+    assert(result == expected);
+    assert(result.get_allocator() == allocator);
+    LIBCPP_ASSERT(is_string_asan_correct(st + sv));
+  }
+  // const string& + string_view
+  {
+    const std::basic_string<CharT, TraitsT, AllocT> st{x, allocator};
+    std::basic_string_view<CharT, TraitsT> sv{y};
+
+    std::same_as<std::basic_string<CharT, TraitsT, AllocT>> decltype(auto) result = st + sv;
+    assert(result == expected);
+    assert(result.get_allocator() == allocator);
+    LIBCPP_ASSERT(is_string_asan_correct(st + sv));
+  }
+  // string&& + string_view
+  {
+    std::basic_string<CharT, TraitsT, AllocT> st{x, allocator};
+    std::basic_string_view<CharT, TraitsT> sv{y};
+
+    std::same_as<std::basic_string<CharT, TraitsT, AllocT>> decltype(auto) result = std::move(st) + sv;
+    assert(result == expected);
+    assert(result.get_allocator() == allocator);
+    LIBCPP_ASSERT(is_string_asan_correct(std::move(st) + sv));
+  }
+  // string_view + string&
+  {
+    std::basic_string_view<CharT, TraitsT> sv{x};
+    std::basic_string<CharT, TraitsT, AllocT> st{y, allocator};
+
+    std::same_as<std::basic_string<CharT, TraitsT, AllocT>> decltype(auto) result = sv + st;
+    assert(result == expected);
+    assert(result.get_allocator() == allocator);
+    LIBCPP_ASSERT(is_string_asan_correct(sv + st));
+  }
+  // string_view + const string&
+  {
+    std::basic_string_view<CharT, TraitsT> sv{x};
+    const std::basic_string<CharT, TraitsT, AllocT> st{y, allocator};
+
+    std::same_as<std::basic_string<CharT, TraitsT, AllocT>> decltype(auto) result = sv + st;
+    assert(result == expected);
+    assert(result.get_allocator() == allocator);
+    LIBCPP_ASSERT(is_string_asan_correct(sv + st));
+  }
+  // string_view + string&&
+  {
+    // Create a `basic_string` to workaround clang bug:
+    // https://github.com/llvm/llvm-project/issues/92382
+    // Comparison between pointers to a string literal and some other object results in constant evaluation failure.
+    std::basic_string<CharT, TraitsT, AllocT> st_{x, allocator};
+    std::basic_string_view<CharT, TraitsT> sv{st_};
+    std::basic_string<CharT, TraitsT, AllocT> st{y, allocator};
+
+    std::same_as<std::basic_string<CharT, TraitsT, AllocT>> decltype(auto) result = sv + std::move(st);
+    assert(result == expected);
+    assert(result.get_allocator() == allocator);
+    LIBCPP_ASSERT(is_string_asan_correct(sv + std::move(st)));
+  }
----------------
dangelog wrote:

Would it also make sense to test `string + convertible_to_string_view` ?

https://github.com/llvm/llvm-project/pull/88389