bug#37045: lisp-indent-region hangs in lisp-indent-calc-next when indenting the three characters "|#\n"

[Noam Postavsky]

found 37045 26.1
tags 37045 + patch
quit

eschulte@grammatech.com writes:

> Indent-region sometimes hangs when indenting a lisp file.  A minimal
> example is the file just containing the characters "|#" followed by a
> newline.

It's actually any unfinished string literal (in Common Lisp, |...| is
treated by Emacs as a string literal, though technically it's an escaped
symbol).

> This hang is due to an infinite loop in the while loop in the
> `lisp-indent-calc-next' function.  The following version of this
> function fixes this problem, but is certainly not the appropriate
> long-term fix.

I think the right fix is just to check for end of buffer:

@@ -810,7 +810,7 @@ lisp-indent-calc-next
                (setq last-sexp (nth 2 ppss)))
              (setq depth (car ppss))
              ;; Skip over newlines within strings.
-             (nth 3 ppss))
+             (and (not (eobp)) (nth 3 ppss)))
       (let ((string-start (nth 8 ppss)))
         (setq ppss (parse-partial-sexp (point) (point-max)
                                        nil nil ppss 'syntax-table))

Full patch with test (and some other comment updates) attached below.
Is this okay for emacs-26?  The bug is a regression from Emacs 25.

0001-Fix-lisp-indent-infloop-on-unfinished-strings-Bug-37.patch
Description: patch