Assertion failed: "List initialization must have initializer list as expression."

[dcci]

$ ./clang "-cc1" "-o" "/dev/null" -std=c++1y "-x" "c++"  pat.cpp
Assertion failed: ((!ListInitialization || (Exprs.size() == 1 && isa<InitListExpr>(Exprs[0]))) && "List initialization must have initializer list as expression."), function BuildCXXTypeConstructExpr, file SemaExprCXX.cpp, line 1457.

$ cat pat.cpp
namespace std {
template <class _Tp> class vector {};
} // namespace std                                                                                                                        

template <typename T>
class Vector : public std::vector<T> {};

struct S {
  S();
  template <class Dummy> void f();
  const Vector<int> &g();
};

S::S() {
  f<int>();
}

template <class Dummy>
void S::f() {
  __attribute__((unused)) auto _ =
    decltype(g()){};
}

[dcci]

cc: @AaronBallman

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[llvmbot]

@llvm/issue-subscribers-c-14

[AaronBallman]

At first I thought this might be a duplicate of #58302 because the assertions happen in the "same" place (line numbers are different but that's not unexpected), however, they seem to be distinct cases. This bug report only asserts in C++14 mode (works fine in C++17 and C++20).

[shafik]

I am on vacation but @AaronBallman have you checked if we are getting a CXXTemporaryObjectExpr like the other case. This is near the top of my list of crash bugs to look at when I get back. I am pretty sure the assert is not correct anymore but I need to dig into it some more to see what the full consequences are.

[AaronBallman]

I am on vacation but @AaronBallman have you checked if we are getting a CXXTemporaryObjectExpr like the other case.

Yes, that is what's happening. There's one expression in the init list and it's a temporary object expr. I'll leave this one to you (and if you think it's the same as the other report, feel free to close one as a duplicate of the other). However, most importantly: go enjoy your vacation!

[dcci]

@shafik are you looking at this one, or you'd like me to look at? We're hitting this internally.