Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.

[moralismercatus]

Bugzilla Link	48324
Version	11.0
OS	Linux
Attachments	.ii, .cpp, .sh and backtrace associated files.
CC	@dwblaikie,@zygoloid

Extended Description

Front-end assertion while compiling dry-comparison library code.

Briefly tested code compilation godbolt.org. Clang-6 compiles. Clang versions subsequent to 6 fail with the noted assertion.

See attached files for details.

Thanks,

[Endilll]

Appears to be fixed on post-17 trunk: https://godbolt.org/z/Mj97b3bY4
Reduced by C-Reduce:

auto tuple = [](auto... ts) {
  return [](auto f) -> decltype(f(ts...)) {}
} auto or_elements = [](auto func) {
  return [](auto... elements) -> decltype((func(elements) || ...)) {}
};
template <typename Func, typename Tuple> struct op_t {
  Tuple tup;
  Func func;
  template <typename E> auto apply(E e) -> decltype(tup(func(e)));
  op_t(int , Func , Tuple ;
  template < typename RH > auto operator==(RH rh)  -> decltype(apply(rh));
  template < typename LH > friend auto operator==(LH lh, op_t rh) -> decltype(rh == lh)
} auto none_of = [](auto... ts) { return op_t(0, nor_elements, tuple (ts ...)
} void main() {
  0 == none_of(int{})

[llvmbot]

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