[libcxx-commits] [libcxx] [libc++][format] P2637R3: Member `visit` (`std::basic_format_arg`) (PR #76449)

[Mark de Wever via libcxx-commits]

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@@ -0,0 +1,64 @@
+//===----------------------------------------------------------------------===//
+// 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
+// UNSUPPORTED: GCC-ALWAYS_INLINE-FIXME
+
+// <format>
+
+// template<class Visitor, class Context>
+//   see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
+
+#include <algorithm>
+#include <cassert>
+#include <format>
+#include <type_traits>
+
+#include "constexpr_char_traits.h"
+#include "make_string.h"
+#include "min_allocator.h"
+#include "test_macros.h"
+
+template <class Context, class To, class From>
+void test(From value) {
+  auto store = std::make_format_args<Context>(value);
+  std::basic_format_args<Context> format_args{store};
+
+  LIBCPP_ASSERT(format_args.__size() == 1);
+  assert(format_args.get(0));
+
+  // non-member
+  {
+    // expected-warning at +1 {{std::basic_format_context<char *, char>>' is deprecated}}
+    std::visit_format_arg(
+        [v = To(value)](auto a) -> To {
+          if constexpr (std::is_same_v<To, decltype(a)>) {
+            assert(v == a);
+            return a;
+          } else {
+            assert(false);
+            return {};
+          }
+        },
+        format_args.get(0));
+  }
+}
+
+template <class CharT>
+void test() {
+  using Context = std::basic_format_context<CharT*, CharT>;
+  std::basic_string<CharT> empty;
+  std::basic_string<CharT> str = MAKE_STRING(CharT, "abc");
+
+  test<Context, bool>(true);
+}
+
+int main(int, char**) {
+  test<char>();
+
+  return 0;
+}
----------------
mordante wrote:

Verify tests are never executed so we prefer not to have `main` in them.
Can you reduce the test to it's bare minimum to trigger the deprecation message for `char` and `wchar_t`?

https://github.com/llvm/llvm-project/pull/76449