Clang with -std=c++2a crashes on invalid recursive variadic template struct definition

[rgreenblatt]

This happens with 10 rc2/rc3 and latest dev built from source.

This is a pretty minimal reproduction:

template <char First, char... Rest> struct Recursive {
  using next = typename Recursive<Rest...>::type;
  using type = notdefined<next::anything>;
};

Build with clang++ -std=c++2a test.cpp
It doesn't crash with -std=c++17

I made a docker container which reproduces the issue.

backtrace.txt

Here is a zip with the backtrace, preprocessed source and associated run script.
bug-report.zip

[rgreenblatt]

I ran into this when including some parts of libstdc++ and having errors from elsewhere. The fact that the struct in this case is invalid may not be the root cause of the issue.

[zmodem]

Bisection points to this commit:

---

commit 67c608a
Author: Saar Raz saar@raz.email
Date: Fri Jan 24 00:43:22 2020 +0200

[Concepts] Deprecate -fconcepts-ts, enable Concepts under -std=c++2a  
                                                                                           
Now with concepts support merged and mostly complete, we do not need -fconcepts-ts
(which was also misleading as we were not implementing the TS) and can enable
concepts features under C++2a. A warning will be generated if users still attempt
to use -fconcepts-ts.

---

@saarraz can you take a look?

[saarraz]

Will do in a few hours

…

On Mon, Mar 16, 2020, 12:56 PM Hans ***@***.***> wrote: Bisection points to this commit: ------------------------------ commit 67c608a <67c608a> Author: Saar Raz ***@***.*** Date: Fri Jan 24 00:43:22 2020 +0200 [Concepts] Deprecate -fconcepts-ts, enable Concepts under -std=c++2a Now with concepts support merged and mostly complete, we do not need -fconcepts-ts (which was also misleading as we were not implementing the TS) and can enable concepts features under C++2a. A warning will be generated if users still attempt to use -fconcepts-ts. ------------------------------ @saarraz <https://github.com/saarraz> can you take a look? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#181 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABCB37LBXZLDXU7S2624XL3RHYAWJANCNFSM4LJOIAVA> .

[saarraz]

Fixed 19fccc5

[rgreenblatt]

This seems to be resolved, and I can't get any more crashes when using trunk.