Extended Description

The following example is given both in the current C++ draft standard: http://eel.is/c++draft/expr.const#11 and the immediate functions proposal: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1073r3.html

consteval int f() { return 42; }
consteval auto g() { return f; }
consteval int h(int (*p)() = g()) { return p(); }
constexpr int r = h(); // OK

and although examples not normative AFAICT this is meant to be valid but clang rejects this although gcc does accept it, see the following godbolt: https://godbolt.org/z/WW7G9q