bug#29710: Emacs becomes unresponsive when typing brackets (haskell-mode)

[Noam Postavsky <npostavs@users.sourceforge.net>]

On Thu, Dec 14, 2017 at 12:05 PM, Hariharan Rangasamy
<hariharanrangasamy@gmail.com> wrote:
> Emacs becomes unresponsive when typing {-[]-} when both haskell mode and
> electric pair mode are enabled.
>
> Install haskell mode from https://github.com/haskell/haskell-mode
>
> * emacs -Q
> * enable electric-pair-mode
> * enable haskell mode in scratch buffer
> * type {--}
> * try to input brackets
> {-[]-}
>
> On pressing [  emacs becomes unresponsive, the mouse pointer rotates
> continuously. On giving C-g repeatedly, the brackets are inserted and
> emacs becomes responsive again. Also when i send SIGUSR2 signal emacs
> becomes responsive.
>
> The bug was posted in
> https://www.reddit.com/r/emacs/comments/7jb4qu/bug_with_haskellmode_and_electricpairmode_doesnt/
> In the original post the user mentioned emacs was crashing but i was
> able to reproduce the emacs hang only.
>
> I was able to reproduce this issue easily on two different systems.
> Let me know if you are unable to reproduce the issue or if you need
> more info.

I can reproduce also in 25.3, not in 24.5. Probably same issue as
Bug#23443, i.e., electric-pair-mode needs to clear the cache after it
finishes messing with the syntax table.