[clang] std::views::zip causes "error: type constraint differs in template redeclaration"

[somecho]

Hello! Compiling this example from cppreference works with GCC 13.2 but not Clang 17.0.1 using -std=c++23 flag. See comparison on godbolt.

#include <array>
#include <iostream>
#include <list>
#include <ranges>
#include <string>
#include <tuple>
#include <vector>
 
void print(auto const rem, auto const& range)
{
    for (std::cout << rem; auto const& elem : range)
        std::cout << elem << ' ';
    std::cout << '\n';
}
 
int main()
{
    auto x = std::vector{1, 2, 3, 4};
    auto y = std::list<std::string>{"α", "β", "γ", "δ", "ε"};
    auto z = std::array{'A', 'B', 'C', 'D', 'E', 'F'};
 
    print("Source views:", "");
    print("x: ", x);
    print("y: ", y);
    print("z: ", z);
 
    print("\nzip(x,y,z):", "");
 
    for (std::tuple<int&, std::string&, char&> elem : std::views::zip(x, y, z))
    {
        std::cout << std::get<0>(elem) << ' '
                  << std::get<1>(elem) << ' '
                  << std::get<2>(elem) << '\n';
 
        std::get<char&>(elem) += ('a' - 'A'); // modifies the element of z
    }
 
    print("\nAfter modification, z: ", z);
}

Clangd 19.1.2 also complains:

[EugeneZelenko]

main seems OK: https://godbolt.org/z/bsscGKbvb. Please note that only most recent release (19 as of now) is maintained.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Somē Cho (somecho)

Hello! Compiling this example from [cppreference](https://en.cppreference.com/w/cpp/ranges/zip_view) works with GCC 13.2 but not Clang 17.0.1 using `-std=c++23` flag. See comparison on [godbolt](https://godbolt.org/z/KabY5Mhcz).

#include <array>
#include <iostream>
#include <list>
#include <ranges>
#include <string>
#include <tuple>
#include <vector>
 
void print(auto const rem, auto const& range)
{
    for (std::cout << rem; auto const& elem : range)
        std::cout << elem << ' ';
    std::cout << '\n';
}
 
int main()
{
    auto x = std::vector{1, 2, 3, 4};
    auto y = std::list<std::string>{"α", "β", "γ", "δ", "ε"};
    auto z = std::array{'A', 'B', 'C', 'D', 'E', 'F'};
 
    print("Source views:", "");
    print("x: ", x);
    print("y: ", y);
    print("z: ", z);
 
    print("\nzip(x,y,z):", "");
 
    for (std::tuple<int&, std::string&, char&> elem : std::views::zip(x, y, z))
    {
        std::cout << std::get<0>(elem) << ' '
                  << std::get<1>(elem) << ' '
                  << std::get<2>(elem) << '\n';
 
        std::get<char&>(elem) += ('a' - 'A'); // modifies the element of z
    }
 
    print("\nAfter modification, z: ", z);
}

Clangd 19.1.2 also complains:

[shafik]

Looks like this started working in clang-19: https://godbolt.org/z/hGbvvT9js

So we won't try and fix this any further back.

[somecho]

Thanks for checking this out. For those that may encounter the same issue, after updating to Clang 19.1.4, the example still wouldn't compile with -std=c++23 only and the -stdlib=libc++ flag was also needed (which is not the case in Godbolt).