How to change the face of a long line without affecting other font-lock customizations in Emacs?

Question

I have some code that I borrowed from a long while ago that sets a long-line face when the line is too long:

 (add-hook 'font-lock-mode-hook
           (function
            (lambda ()
              (setq font-lock-keywords
                    (append font-lock-keywords
                            '( ("^.\\{133,\\}$" (0 'my-long-line-face t))
                              )
                            )
                    )
              )
            ))

(I know about font-lock-add-keywords now, BTW; like I said, this is kind of old.)

The problem is that this changes the face of the entire line. So if I indicate that long-line-face is bold, I lose all the contextual customization of the line, and it appears in the default face, but bold.

How would I get it to keep the contextual colouring but make everything bold?

I used to do this, but I like the fill-column-indicator library better now. http://www.emacswiki.org/emacs/FillColumnIndicator — Michael Hoffman, Nov 30 '11 at 23:32
See the `See also` on the page Michael H. mentioned, for several other ways to highlight or otherwise indicate long lines. — Drew, Dec 01 '11 at 04:46
I actually checked emacswiki first, but I didn't like any of the solutions there. — RealityMonster, Dec 01 '11 at 15:49

scottfrazer · Accepted Answer · 2011-12-01T20:59:40.073

2

You are overriding the fontification with the t in your font-lock spec. Try changing the (0 'my-long-line-face t) to either (0 'my-long-line-face prepend) or (0 'my-long-line-face append).

edited Dec 01 '11 at 20:59

answered Nov 30 '11 at 22:14

scottfrazer

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Correct, with one minor correction. It needs to be either (0 'my-long-line-face prepend) or (0 'my-long-line-face append). But now it works like a charm; I didn't know about append and prepend. :) – RealityMonster Dec 01 '11 at 15:42

score 1 · Answer 2 · answered Nov 30 '11 at 20:25

Try this modification to your code:

(add-hook 'font-lock-mode-hook
       (function
    (lambda ()
      (setq font-lock-keywords
        (append font-lock-keywords
            '( ("^.\\{133\\}\\(.*\\)$" (1 'my-long-line-face t))
              )
            )
        )
      )
    ))

The key being that you want the regexp to have a sub expression that follows the 133 characters that aren't too long, and then apply my-long-line-face to that following sub expression - as indicated by the 1 (instead of the 0 that you had). See the info page for Search-based Fontification for more details.

Definitely works as advertised, but I wanted something more like the answer scottfrazer gave. Thanks! — RealityMonster, Dec 01 '11 at 15:43

How to change the face of a long line without affecting other font-lock customizations in Emacs?

2 Answers2