(Sudden) Weird behavior of M-q in auctex

Question

I very much enjoying using the auto fill functionality that the key binding M-q provides. However, starting recently, I am experiencing a small (but annoying) change in its behavior when in LaTeX mode. That is, now I have to explicitly mark the paragraph that I want to auto fill, whereas before it was good enough as long as the cursor is somewhere in the paragraph. For example, to format

Hello 
World

to

Hello World

it was enough to hit M-q with my cursor somewhere in those two lines. Now I have to mark the two lines and then hit M-q to get the reformatting. I haven't installed anything new or touched my configuration file. I did update Emacs a couple days ago. Any advice will be greatly appreciated.

Answer 1

Entries in LaTeX-indent-environment-list control the filling behavior in environments. If you want the standard filling AUCTeX applies to environments, remove entries for your appendices from it and M-q should work again.

The appendices environment is provided by LaTeX package appendix.sty. In order to get auto-completion for it when you hit C-c C-e, you need a small AUCTeX style appendix.el which makes the addition to AUCTeX. Such a style can look like this:

(TeX-add-style-hook
 "appendix"
 (lambda ()

   (TeX-add-symbols
    "appendixpage"
    "addappheadtotoc"
    "noappendicestocpagenum"
    "appendicestocpagenum"
    "appendixname"
    "appendixtocname"
    "appendixpagename"

    "appendixtocon"
    "appendixtocoff"
    "appendixpageon"
    "appendixpageoff"
    "appendixtitleon"
    "appendixtitleoff"
    "appendixtitletocon"
    "appendixtitletocoff"
    "appendixheaderon"
    "appendixheaderoff"
    "restoreapp"

    "setthesection"
    "setthesubsection")

   (LaTeX-add-environments
    '("appendices")
    '("subappendices"))

   ;; Don't indent the content inside \(sub\)?appendices environments:
   (unless (string-match "appendices" LaTeX-document-regexp)
     (set (make-local-variable 'LaTeX-document-regexp)
          (concat LaTeX-document-regexp "\\|\\(?:sub\\)?appendices"))))
 LaTeX-dialect)

(defvar LaTeX-appendix-package-options '("toc" "page" "title"
                                         "titletoc" "header")
  "Package options for the appendix package.")

Set the variable TeX-style-private to a directory of your choice, e.g.

(setq TeX-style-private
      '("~/.emacs.d/auctex-styles"))

and save the code above there as appendix.el. Now re-start Emacs and open your .tex file. If you have this in your init file as well

(setq TeX-parse-self t)

the auto-completion should be available directly.