[llvm-bugs] [Bug 44538] New: Unsized temporary array problem inside template function

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https://bugs.llvm.org/show_bug.cgi?id=44538

            Bug ID: 44538
           Summary: Unsized temporary array problem inside template
                    function
           Product: clang
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: m.cencora at gmail.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

Temporary unsized arrays declared inside function template, are treated as
unsized in some contexts, and as sized in others.
I.e. decltype always returns int (&&)[3], but range based for-loop sometimes
treats it as unsized (and incomplete).

Reproducer:

#include <type_traits>

using Array = int[];

template <typename ...Ts>
void bar1(Ts ...values)
{
    auto && array1 = Array{ 1, 2, 3 };
    auto && array2 = Array{ values...};

    static_assert(std::is_same<int (&&)[3], decltype(array1)>{}, "");      //
ok
    static_assert(std::is_same<decltype(array1), decltype(array2)>{}, ""); //
ok

    for (auto c : array1) {} // ok
    for (auto c : array2) {} // does not compile, says array2 has incomplete
type int[]
}

template <typename T1, typename T2, typename T3>
void bar2(T1 v1, T2 v2, T3 v3)
{
    auto && array1 = Array{ 1, 2, 3 };
    auto && array2 = Array{ v1, v2, v3 };
    auto && array3 = Array{ (int)v1, (int) v2, (int)v3 };

    static_assert(std::is_same<int (&&)[3], decltype(array1)>{}, "");      //
ok
    static_assert(std::is_same<decltype(array1), decltype(array2)>{}, ""); //
ok
    static_assert(std::is_same<decltype(array1), decltype(array3)>{}, ""); //
ok

    for (auto c : array1) {} // ok
    for (auto c : array2) {} // does not compile, says array2 has incomplete
type int[]
    for (auto c : array3) {} // ok
}

void bar3(int a, int b, int c)
{
    auto && array1 = Array{ 1, 2, 3 };
    auto && array2 = Array{ a, b, c };

    static_assert(std::is_same<int (&&)[3], decltype(array1)>{}, "");      //
ok
    static_assert(std::is_same<decltype(array1), decltype(array2)>{}, ""); //
ok

    for (auto c : array1) {} // ok
    for (auto c : array2) {} // ok
}

int main()
{
    bar1<int, int, int>(1, 2, 3);
    bar2<int, int, int>(1, 2, 3);
    bar3(1, 2, 3);
}

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