Clang crash when trying to evaluate a constexpr with `auto` type, variadic template before type is fully defined

[bricknerb]

Example:

struct MyClass {
  template <int...> static constexpr auto foo() { return 1; }
  static constexpr auto my_value = foo();
};

We get a "Unexpected undeduced type!" crash

Compiler Explorer: https://godbolt.org/z/5PKP885K7

I believe this should be an error that says the function foo() isn't defined yet because the class isn't fully defined, but not a crash.

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Boaz Brickner (bricknerb)

Example:

struct MyClass {
  template <int...> static constexpr auto foo() { return 1; }
  static constexpr auto my_value = foo();
};

We get a "Unexpected undeduced type!" crash

Compiler Explorer: https://godbolt.org/z/5PKP885K7

I believe this should be an error that says the function foo() isn't defined yet because the class isn't fully defined, but not a crash.