Assertion `FromType->isIntegralOrUnscopedEnumerationType()' failed when converting between scoped enums

[pcc]

> cat test.ii
enum class a : int;
enum class b : int;

b x{a{}};
> ~/l/ra/bin/clang++ test.ii -std=c++17
clang: ../clang/lib/Sema/SemaOverload.cpp:424: clang::NarrowingKind clang::StandardConversionSequence::getNarrowingKind(clang::ASTContext &, const clang::Expr *, clang::APValue &, clang::QualType &, bool) const: Assertion `FromType->isIntegralOrUnscopedEnumerationType()' failed.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[pcc]

https://reviews.llvm.org/D120862

[shafik]

This code is ill-formed and both gcc and clang currently reject this code and clang no longer seems to assert, see godbolt: https://godbolt.org/z/35MdP5EKv

Note defect report 2374