generic lambda as function parameter fails to be converted to pointer to function

[nickhuang99]

See compiler explorer (https://www.godbolt.org/z/GGxKoYGsx) both GCC and MSVC accepts the following code. Clange rejects by giving error of conversion lambda. According to standard, generic lambda should still be convertible to function pointer which is defined by type decltype(+[](T t )->T{return t+1;})

template<typename T>
auto foo(T t, decltype(+[](T t )->T{return t+1;}) lam){
	return lam(t);
}
void test(){
	foo<int>(5, [](int t){return t+1;});
}

clang13 giving error of

:8:2: error: no matching function for call to 'foo'
        foo(5, [](int t){return t+1;});
        ^~~~~~~~
 note: candidate function [with T = int] not viable: no known conversion from '(lambda at :8:14)' to 'decltype(+[](int t) -> int {
    return t + 1;
})' for 2nd argument
auto foo(T t, decltype(+[](T t )->T{return t+1;}) lam){
     ^
1 error generated.
Compiler returned: 1

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[cor3ntin]

This is fixed https://www.godbolt.org/z/MsThM8jdT