Emacs+AUCTeX: Improve ConTeXt mode indentation

Question

I’m using Emacs with AUCTeX in ConTeXt-mode to compose my ConTeXt documents. However, indentation is a little bit inconvenient for me.

Consider the following snippet:

\setuphead
  [section]
  [before={\blank[big]},
   after={\blank[medium]}]

\setuphead
  [subsection]
  [
    before={\blank[big]},
    after={\blank[medium]},
  ]

If I execute indent-region onto this, it should not change (it is indented correctly, i.e. it follows the indentation scheme of the ConTeXt source and the indentation scheme by our local ConTeXt expert Aditya). However, Emacs mangles this code to

\setuphead
  [section]
  [before={\blank[big]},
    after={\blank[medium]}]

  \setuphead
    [subsection]
    [
      before={\blank[big]},
      after={\blank[medium]},
    ]

Especially the second \setuphead should not be indented further at this point.

Can anyone provide some Lisp magic to put in my .emacs to make indentation less painful?

Answer 1

Note: this question led to the inclusion of the following fix in AUCTeX. It'll be available in the ELPA version 11.90.3 and the stable version 11.91.

Warning: this answer does almost what you asked.

Add the following function definition to your init file:

(with-eval-after-load "context"
  (defun ConTeXt-find-indent (&optional virtual)
    "Find the proper indentation of text after point.
VIRTUAL if non-nil indicates that we're only trying to find the
indentation in order to determine the indentation of something
else.  There might be text before point."
    (save-excursion
      (skip-chars-forward " \t")
      (or
       ;; Trust the current indentation, if such info is applicable.
       (and virtual (>= (current-indentation) (current-column))
        (current-indentation))
       ;; Put leading close-paren where the matching open brace would be.
       (condition-case nil
       (and (eq (char-syntax (char-after)) ?\))
        (save-excursion
          (skip-syntax-forward " )")
          (backward-sexp 1)
          (ConTeXt-find-indent 'virtual)))
     (error nil))
       ;; Default (maybe an argument)
       (let ((pos (point))
         (char (char-after))
         (indent 0)
         up-list-pos)
     ;; Look for macros to be outdented
     (cond ((looking-at (concat (regexp-quote TeX-esc)
                    (ConTeXt-environment-stop-name)))
        (setq indent (- indent ConTeXt-indent-basic)))
           ((looking-at ConTeXt-indent-item-re)
        (setq indent (- indent ConTeXt-indent-item))))
     ;; Find the previous point which determines our current indentation.
     (condition-case err
         (progn
           (backward-sexp 1)
           (while (or (> (current-column) (current-indentation))
              ;; Continue going back if we are
              ;; at a hanging optional group.
              (looking-at (regexp-quote ConTeXt-optop)))
         (backward-sexp 1)))
       (scan-error
        (setq up-list-pos (nth 2 err))))
     (cond
      ((= (point-min) pos) 0)  ; We're really just indenting the first line.
      ((integerp up-list-pos)
       ;; Have to indent relative to the open-paren.
       (goto-char up-list-pos)
       (if (and (not ConTeXt-indent-allhanging)
            (> pos (progn (down-list 1)
                  (forward-comment (point-max))
                  (point))))
           ;; Align with the first element after the open-paren.
           (current-column)
         ;; We're the first element after a hanging brace.
         (goto-char up-list-pos)
         (+ indent ConTeXt-indent-basic (ConTeXt-find-indent 'virtual))))
      ;; We're now at the "beginning" of a line.
      ((not (and (not virtual) (eq (char-after) ?\\)))
       ;; Nothing particular here: just keep the same indentation.
       (+ indent (current-column)))
      ;; We're now looking at an item.
      ((looking-at ConTeXt-indent-item-re)
       ;; Indenting relative to an item, have to re-add the outdenting.
       (+ indent (current-column) ConTeXt-indent-item))
      ;; We're looking at an environment starter.
      ((and (looking-at (concat (regexp-quote TeX-esc)
                    (ConTeXt-environment-start-name)))
        (not (looking-at (concat (regexp-quote TeX-esc)
                     (ConTeXt-environment-start-name)
                     ConTeXt-text)))) ; other environments?
       (+ indent (current-column) ConTeXt-indent-basic))
      (t
       (let ((col (current-column)))
         (if (not (and char (eq (char-syntax char) ?\()))
         ;; If the first char was not an open-paren, there's
         ;; a risk that this is really not an argument to the
         ;; macro at all.
         (+ indent col)
           (forward-sexp 1)
           (if (< (line-end-position)
              (save-excursion (forward-comment (point-max))
                      (point)))
           ;; we're indenting the first argument.
           (min (current-column) (+ ConTeXt-indent-arg col))
         (skip-syntax-forward " ")
         (current-column)))))))))))

This is a fixed version of the indenting function provided by AUCTeX. There is only a minor change (the (looking-at (regexp-quote ConTeXt-optop)) line) to adjust indentation after [...].

Now your original code is indented as

\setuphead
  [section]
  [before={\blank[big]},
    after={\blank[medium]}]

\setuphead
  [subsection]
  [
    before={\blank[big]},
    after={\blank[medium]},
  ]

The only thing that I couldn't fix was indentation of after={\blank[medium]}] line, but for multiline settings inside [...] I'd suggest you to do like you did in the second case.

Please, tell me if you find this solution useful in the long run, so that I can install this change upstream.