Subject: bug#19892: 25.0.50; hideshow: hs-hide-all-non-comment-function example infloop

From: Michael Heerdegen <[email-masked]>
Date: Tue, 17 Feb 2015 23:45:15 +0100

Hello,

  (CCing the authors of hideshow specified in the file header)

in the header of hideshow.el, we have the following paragraph:

--8<---------------cut here---------------start------------->8---
;; Some languages (e.g., Java) are deeply nested, so the normal behavior
;; of `hs-hide-all' (hiding all but top-level blocks) results in very
;; little information shown, which is not very useful.  You can use the
;; variable `hs-hide-all-non-comment-function' to implement your idea of
;; what is more useful.  For example, the following code shows the next
;; nested level in addition to the top-level:
;;
;;   (defun ttn-hs-hide-level-1 ()
;;     (hs-hide-level 1)
;;     (forward-sexp 1))
;;   (setq hs-hide-all-non-comment-function 'ttn-hs-hide-level-1)
--8<---------------cut here---------------end--------------->8---

But this doesn't always work.  For example, eval the above example in
emacs -Q, open "files.el", M-x hs-minor-mode, M-x hs-hide-all.  You get
an infloop.

AFAICT the definition should be (or at least it works with that)

(defun ttn-hs-hide-level-1 ()
  (when (hs-looking-at-block-start-p)
    (hs-hide-level 1))
  (forward-sexp 1))

Secondly, there is this comment in `hs-hide-all' which confuses me a bit:

;; Go to end of matched data to prevent from getting stuck
;; with an endless loop.

Which match data is meant there?  It is either match data from before
hiding the block - then it should be documented that
`hs-hide-all-non-comment-function' must not change match data, I guess,
or the call should be wrapped into `save-match-data'.  Or it is even the
case that `hs-hide-all-non-comment-function' must set the match data
(how?), which then should probably be documented.

Thanks,

Michael.

In GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.5)
 of 2015-02-15 on drachen
Repository revision: ba5bc0ee7c81f2122072bee162fcf1dbd8b2a8f2
Windowing system distributor `The X.Org Foundation', version 11.0.11602901
System Description:	Debian GNU/Linux 8.0 (jessie)

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS NOTIFY
LIBXML2 FREETYPE XFT ZLIB

Important settings:
  value of $LC_ALL: de_DE.utf8
  value of $LC_COLLATE: C
  value of $LC_TIME: C
  value of $LANG: de_DE.utf8
  locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
  magit-auto-revert-mode: t
  rainbow-delimiters-mode: t
  paredit-mode: t
  on-screen-global-mode: t
  ml-scale-mode: t
  interaction-log-mode: t
  highlight-defined-mode: t
  helm-descbinds-mode: t
  helm-mode: t
  shell-dirtrack-mode: t
  helm-occur-match-plugin-mode: t
  helm-match-plugin-mode: t
  helm-autoresize-mode: t
  global-diff-hl-mode: t
  diff-hl-mode: t
  diff-auto-refine-mode: t
  recentf-mode: t
  which-function-mode: t
  winner-mode: t
  show-paren-mode: t
  auto-image-file-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  mouse-wheel-mode: t
  prettify-symbols-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  hs-minor-mode: t