crash when undeclared template name with dependent template argument used as type

[rgreenblatt]

Bugzilla Link	45207
Resolution	FIXED
Resolved on	Oct 28, 2021 10:05
Version	trunk
OS	Linux
Blocks	#44654
CC	@AaronBallman,@zmodem,@tambry,@zygoloid,@tstellar
Fixed by commit(s)	llvmorg-11-init-6027-gc48442c9f38

Extended Description

I have filed the same bug on github here: #181, but I am posting here for completeness.

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: https://hub.docker.com/r/greenblattryan/clang-crash-recursive-template.

Backtrace: https://github.com/llvm/llvm-project/files/4333084/backtrace.txt

Here is a zip with the backtrace, preprocessed source and associated run script.
https://github.com/llvm/llvm-project/files/4333081/bug-report.zip

[rgreenblatt]

assigned to @zygoloid

[zygoloid]

Further-reduced testcase:

template notdefined<T::any> x;

[zygoloid]

*** Bug #44386 has been marked as a duplicate of this bug. ***

[zmodem]

Re-opening in case we want this for 10.0.1.

[tstellar]

Richard, is this OK to merge to the release/10.x branch?

https://github.com/tstellar/llvm-project/pull/63/files

[zygoloid]

It is, but...

It looks like you already merged 19fccc5. The commit you mentioned above fixed the same bug in a somewhat different way (Saar and I both fixed the bug after it was filed in two different places, and both patches ended up landing). This pull request has no additional functional change, so it's probably not worth merging.

If you do take my patch, I'd suggest also taking the cleanup patch fc8a009 which removes some redundant code left behind by the combination of the two fixes.

[AaronBallman]

Re-closing as 10.x shipped already sailed.

[tstellar]

mentioned in issue #44654