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a760df3165
[CWG2137](https://cplusplus.github.io/CWG/issues/2137.html) This was previously implemented and then reverted in Clang 18 as #77768 This also implements a workaround for [CWG2311](https://cplusplus.github.io/CWG/issues/2311.html), similarly to the 2024-03-01 comment for [CWG2742](https://cplusplus.github.io/CWG/issues/2742.html). The exact wording this tries to implement, relative to the C++26 draft: [over.match.list]p(1.2) > Otherwise, or if no viable initializer-list constructor is found <ins>and the initializer list does not consist of exactly a single element with the same cv-unqualified class type as `T`</ins>, overload resolution is performed again, [...] [dcl.init.list]p(3.7) > Otherwise, if `T` is a class type, constructors are considered. The applicable constructors are enumerated and the best one is chosen through overload resolution. <ins>If no constructor is found and the initializer list consists of exactly a single element with the same cv-unqualified class type as `T`, the object is initialized from that element (by copy-initialization for copy-list-initialization, or by direct-initialization for direct-list-initialization). Otherwise,</ins> if a narrowing conversion (see below) is required [...]
83 lines
2.0 KiB
C++
83 lines
2.0 KiB
C++
// RUN: %clang_cc1 -std=c++17 -fsyntax-only -verify %s
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// This is heavily affected by the speculative resolution applied to CWG2311
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// So behaviour shown here is subject to change.
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// expected-no-diagnostics
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namespace std {
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typedef decltype(sizeof(int)) size_t;
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// libc++'s implementation
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template <class _E>
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class initializer_list
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{
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const _E* __begin_;
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size_t __size_;
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initializer_list(const _E* __b, size_t __s)
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: __begin_(__b),
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__size_(__s)
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{}
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public:
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typedef _E value_type;
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typedef const _E& reference;
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typedef const _E& const_reference;
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typedef size_t size_type;
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typedef const _E* iterator;
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typedef const _E* const_iterator;
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constexpr initializer_list() : __begin_(nullptr), __size_(0) {}
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constexpr size_t size() const {return __size_;}
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const _E* begin() const {return __begin_;}
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const _E* end() const {return __begin_ + __size_;}
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};
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template<typename T>
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struct vector {
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size_t sz;
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constexpr vector() : sz(0) {}
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constexpr vector(initializer_list<T> ilist) : sz(ilist.size()) {}
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constexpr vector(const vector& other) : sz(other.sz) {}
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constexpr std::size_t size() const { return sz; }
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};
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}
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// https://github.com/llvm/llvm-project/pull/77768#issuecomment-1908062472
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namespace Issue1 {
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struct A {
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constexpr A() {}
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};
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struct B {
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int called_ctor;
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constexpr explicit B(A) : called_ctor(0) {}
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constexpr explicit B(std::vector<A>) : called_ctor(1) {}
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};
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struct C {
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B b;
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constexpr C() : b({A()}) {}
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};
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static_assert(C().b.called_ctor == 0);
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}
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// https://github.com/llvm/llvm-project/pull/77768#issuecomment-1957171805
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namespace Issue2 {
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struct A {
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constexpr A(int x_) {}
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constexpr A(const std::vector<A>& a) {}
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};
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void f() {
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constexpr std::vector<A> a{1,2};
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constexpr std::vector<A> b{a};
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// -> constexpr std::vector<A> b(std::initializer_list<A>{ A(a) });
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static_assert(b.size() == 1);
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}
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}
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