Emacs 25+, scan-sexp with standard syntax table causes infloop in syntax propertize

[npostavs]

This is a minimal example reduced from joaotavora/yasnippet#687.

In a git checkout of lates master (5d58314) emacs -Q -L . -l haskell-autoloads -l synprop-bug.el causes an infinite loop. After hitting C-g, *Messages* contains Error during redisplay: (internal--syntax-propertize 6) signaled (quit). synprop-bug.el contains:

(switch-to-buffer "hh")
(haskell-mode)
(erase-buffer)
(insert "{-# foo #-}")
(with-syntax-table (standard-syntax-table)
  (scan-sexps 5 1))

This doesn't happen in Emacs 24.5, so it may be a bug in Emacs.

[gracjan]

Hmm, even if haskell-propertize would not hang I do not see it producing correct result when syntax-table is not the one it expects.

Then I do not see why yasnippets try to use different syntax table than is defined in the buffer. What is the point of messing with syntax table?

[npostavs]

Because it's parsing yasnippet syntax, which is independent of the major mode's syntax. So it looks like the question is why does yasnippet's temporary syntax-table manipulation affect the syntax propertize function in Emacs 25, but not earlier? I will open an Emacs bug.

EDIT: Emacs bug #23443

[gracjan]

Great. Thanks.

[npostavs]

The conclusion from the Emacs bug discussion is that it's expected behaviour, I will fix this in yasnippet (joaotavora/yasnippet#695)

[gracjan]

Good, thanks.