Customizing tab behavior for "%" comment in prolog-mode (emacs)

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#1

I’m using Stefan Bruda’s Prolog mode for emacs but I find the behavior with tab and “%” to be annoying … it always indents comments to column 32 (variable comment-column), even for lines starting with “%!”.

How can I change this behaviour? If I set comment-column to 0, then single-line comments get indented incorrectly:

foo :-
% this is a comment
    bar.

instead of

foo :-
    % this is a comment
    bar.

and if I leave comment-column at 32, then I get the following, which I don’t want:

                              %! foo is det.
foo :-
                              % this is a comment
    bar.
#3

I think I’ve linked this to you before, but I’m using a slightly-modified version of the prolog.el that I think comes with Emacs that doesn’t seem to have this issue with indenting (I originally started working on this to fix the indentation of terms with dictionaries & character things like 0'.).

Probably a good idea…

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#4

I met the same problem recently, but it seems to have been fixed by:

(setq prolog-align-small-comments-flag nil)

Then the single-line comments get indented:

foo :-
  % this is a comment
  bar.

One new customizable variable has been added in version 1.28:

prolog-align-small-comments-flag (group “Prolog Indentation”) specifies how to handle “small” comments (the ones that start with a simgle “%”) as follows: When this variable is non-nil (default) small comments are aligned to comment-column' (default 32) in all circumstances. When the variable is set to nil however small comments that begin a line (blank characters notwithstanding) will be treated just like “large” comments (the ones that start with “%%”). Note that small comments that start somewhere other than at the beginning of the line are still aligned to comment-column’.

#5

Also, the latest version (1.29) has a bug, I don’t know if it exists in the old version though, is that prolog-indent-buffer doesn’t work properly in some cases. The root cause is that the prolog-indent-line may throw an error “Beginning of buffer”.

It could be work around by advising:

(defun prolog-indent-line/around (orig-fun &rest args)
  (save-excursion
    (condition-case nil
        (apply orig-fun args)
      (beginning-of-buffer 'noindent))))

(advice-add 'prolog-indent-line :around  #'prolog-indent-line/around)

PS. At the writing time, Stefan Bruda’s Prolog mode for emacs’ website said the prolog-mode is version 1.28, but it is actually 1.29. This may cause some confusion.