How to add syntax highlighting inside comments for an existing major mode

How to add syntax highlighting inside comments for an existing major mode

[Julien Barnier]

Hi all,

I am trying to customize some syntax highlighting for an existing
major mode. What I would like to do is to display different type of
comments with different faces.

In this mode, comments are lines that begins with one or several
«#». What I would like to display differently those which begin with
«#####» than those which begin with «####», etc.

I tried the 'font-lock-add-keywords' way, but it doesn't seem to work
inside comments, with something like that :

(font-lock-add-keywords 'ess-mode
  '(("^##### .*$" . my-beautiful-face)))

Do you have any idea for a proper way to do such a thing ?

Thanks in advance for any help.

-- 
Julien

Re: How to add syntax highlighting inside comments for an existing major mode

[Michaël Cadilhac]

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Julien Barnier <jbarnier@ens-lsh.fr> writes:

> In this mode, comments are lines that begins with one or several
> «#». What I would like to display differently those which begin with
> «#####» than those which begin with «####», etc.

The simplest way to achieve that is the following, IMO :

(add-hook 'your-mode-hook
          (lambda ()
            (highlight-regexp "^# .*" 'hi-blue)
            (highlight-regexp "^## .*" 'hi-red-b)))

-- 
 |   Michaël `Micha' Cadilhac       |  In a World without Walls and Fences,  |
 |   http://michael.cadilhac.name   |     who needs Windows and Gates?       |
 |   JID/MSN:                       |          -- Dino Esposito              |
 `----  michael.cadilhac@gmail.com  |                                   -  --'

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Re: How to add syntax highlighting inside comments for an existing major mode

[Johan Bockgård]

Julien Barnier <jbarnier@ens-lsh.fr> writes:

> In this mode, comments are lines that begins with one or several
> «#». What I would like to display differently those which begin with
> «#####» than those which begin with «####», etc.
>
> I tried the 'font-lock-add-keywords' way, but it doesn't seem to work
> inside comments, with something like that :
>
> (font-lock-add-keywords 'ess-mode
>   '(("^##### .*$" . my-beautiful-face)))
>

(info "(elisp)Search-based Fontification")

  `(MATCHER . SUBEXP-HIGHLIGHTER)'
       In this kind of element, SUBEXP-HIGHLIGHTER is a list which
       specifies how to highlight matches found by MATCHER.  It has the
       form:

            (SUBEXP FACESPEC [[OVERRIDE [LAXMATCH]])

       The CAR, SUBEXP, is an integer specifying which subexpression of
       the match to fontify (0 means the entire matching text).  The
       second subelement, FACESPEC, is an expression whose value
       specifies the face, as described above.

       The last two values in SUBEXP-HIGHLIGHTER, OVERRIDE and LAXMATCH,
       are optional flags.  If OVERRIDE is `t', this element can override
       existing fontification made by previous elements of
       `font-lock-keywords'.  If it is `keep', then each character is
       fontified if it has not been fontified already by some other
       element.  If it is `prepend', the face specified by FACESPEC is
       added to the beginning of the `font-lock-face' property.  If it is
       `append', the face is added to the end of the `font-lock-face'
       property.

       [...]

       Here are some examples of elements of this kind, and what they do:

            ;; Highlight occurrences of either `foo' or `bar', using
            ;; `foo-bar-face', even if they have already been highlighted.
            ;; `foo-bar-face' should be a variable whose value is a face.
            ("foo\\|bar" 0 foo-bar-face t)

-- 
Johan Bockgård

Re: How to add syntax highlighting inside comments for an existing major mode

[martin rudalics]

 > I am trying to customize some syntax highlighting for an existing
 > major mode. What I would like to do is to display different type of
 > comments with different faces.
 >
 > In this mode, comments are lines that begins with one or several
 > «#». What I would like to display differently those which begin with
 > «#####» than those which begin with «####», etc.
 >
 > I tried the 'font-lock-add-keywords' way, but it doesn't seem to work
 > inside comments, with something like that :
 >
 > (font-lock-add-keywords 'ess-mode
 >   '(("^##### .*$" . my-beautiful-face)))
 >
 > Do you have any idea for a proper way to do such a thing ?

Write your own `font-lock-syntactic-face-function' and do

   (setq font-lock-defaults
	'(...
	  (font-lock-syntactic-face-function
	   . my-font-lock-syntactic-face-function))))

(defun my-font-lock-syntactic-face-function (state)
   (if (nth 3 state)
       (...)
     ;; Here investigate STATE and decide which face to use.
    ))