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