1 | //===----------------------------------------------------------------------===// |
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | |
9 | // UNSUPPORTED: c++03, c++11, c++14, c++17 |
10 | |
11 | // XFAIL: availability-fp_to_chars-missing |
12 | |
13 | // The sample code is based on the bug report |
14 | // https://github.com/llvm/llvm-project/issues/81590 |
15 | // |
16 | // Tests whether this formatter does not fail to compile due to nested concept |
17 | // evaluation. |
18 | |
19 | #include <format> |
20 | #include <variant> |
21 | |
22 | struct X : std::variant<X*> { |
23 | X* p = nullptr; |
24 | constexpr const std::variant<X*>& decay() const noexcept { return *this; } |
25 | }; |
26 | |
27 | template <> |
28 | struct std::formatter<X, char> : std::formatter<std::string, char> { |
29 | static constexpr auto format(const X& x, auto& ctx) { |
30 | if (!x.p) |
31 | return ctx.out(); |
32 | auto m = [&](const X* t) { return std::format_to(ctx.out(), "{}" , *t); }; |
33 | return std::visit(m, x.decay()); |
34 | } |
35 | }; |
36 | |
37 | void bug_81590() { (void)std::format("{}" , X{}); } |
38 | |