I run into an issue lately while trying to use the hexl-mode with
a modula2 file that I found and emacs starts to hang after the
hexl-mode starts. I tested it on emacs 24.5, 25.2 and master.
To reproduce the issue you can use :
echo "abcd" > test.MOD
emacs -Q --eval '(show-paren-mode 1)' test.MOD
--> emacs hangs and use 100% cpu. It only happen on the first character so
we can run out the hang with multiple C-g + an arrow key.
I dig into the issue and it appears that the was because of the
show-paren-mode and the fact that the ":" character have meaning in
modula-2-mode. Emacs is stuck in the loop of the
m2-smie-refine-colon function because after the "00000000" that start
the hexl buffer there is no more sexp to parse so the tok variable is
empty but the (forward-sexp -1) call does not fail.
I fixed that myself by stopping the loop if the point is at the beginning
of the buffer. Not sure if it correct but here is the diff :
diff --git a/lisp/progmodes/modula2.el b/lisp/progmodes/modula2.el
index 582e495..30c8c46 100644
@@ -203,6 +203,7 @@ m2-smie-refine-colon
(while (not res)
(let ((tok (smie-default-backward-token)))
+ ((= (point) (point-min)) (setq res ":"))
((zerop (length tok))
(let ((forward-sexp-function nil))
I am not really into modula2 files but this bug was quite surprising.