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6d43aad742
Also add test to make sure this doesn't get broken in the future. This was breaking vector<bool> serialization in multiprocess code because template current deduction guides would make it appear like vector<bool> could be converted to a span, but then the actual conversion to span would fail.
73 lines
2.1 KiB
C++
73 lines
2.1 KiB
C++
// Copyright (c) 2023 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include <span.h>
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#include <boost/test/unit_test.hpp>
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#include <array>
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#include <set>
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#include <vector>
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namespace {
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struct Ignore
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{
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template<typename T> Ignore(T&&) {}
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};
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template<typename T>
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bool Spannable(T&& value, decltype(Span{value})* enable = nullptr)
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{
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return true;
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}
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bool Spannable(Ignore)
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{
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return false;
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}
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#if defined(__clang__)
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# pragma clang diagnostic push
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# pragma clang diagnostic ignored "-Wunneeded-member-function"
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# pragma clang diagnostic ignored "-Wunused-member-function"
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#endif
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struct SpannableYes
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{
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int* data();
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size_t size();
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};
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struct SpannableNo
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{
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void* data();
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size_t size();
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};
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#if defined(__clang__)
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# pragma clang diagnostic pop
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#endif
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} // namespace
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BOOST_AUTO_TEST_SUITE(span_tests)
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// Make sure template Span template deduction guides accurately enable calls to
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// Span constructor overloads that work, and disable calls to constructor overloads that
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// don't work. This makes it is possible to use the Span constructor in a SFINAE
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// contexts like in the Spannable function above to detect whether types are or
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// aren't compatible with Spans at compile time.
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//
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// Previously there was a bug where writing a SFINAE check for vector<bool> was
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// not possible, because in libstdc++ vector<bool> has a data() memeber
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// returning void*, and the Span template guide ignored the data() return value,
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// so the template substitution would succeed, but the constructor would fail,
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// resulting in a fatal compile error, rather than a SFINAE error that could be
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// handled.
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BOOST_AUTO_TEST_CASE(span_constructor_sfinae)
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{
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BOOST_CHECK(Spannable(std::vector<int>{}));
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BOOST_CHECK(!Spannable(std::set<int>{}));
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BOOST_CHECK(!Spannable(std::vector<bool>{}));
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BOOST_CHECK(Spannable(std::array<int, 3>{}));
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BOOST_CHECK(Spannable(Span<int>{}));
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BOOST_CHECK(Spannable("char array"));
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BOOST_CHECK(Spannable(SpannableYes{}));
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BOOST_CHECK(!Spannable(SpannableNo{}));
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}
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BOOST_AUTO_TEST_SUITE_END()
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