Strange interaction with whitespace-mode’s highlighting of long lines

[guillaumebrunerie]

I’m using js2-mode together with whitespace-mode to highlight the part of the line that is over 80 characters, and it seems like the syntax highlighting gets messed up somehow. This doesn’t happen with js-mode or other major modes.

Steps to reproduce:
Start emacs with -Q and evaluate the following lines (assuming js2-mode is installed)

(require 'package)
(package-initialize)
(global-whitespace-mode)
(setq whitespace-style '(face lines-tail))
(set-face-attribute 'whitespace-line nil :background "Blue" :foreground nil)

Now open a new .js file, activate js2-mode, and write a long syntactically correct line (long enough that the end becomes blue)

var xxxxxxxxxxxxxxx = 3;

Now add // at the beginning of the line, and note that only the beginning of the line got updated to a red foreground color, the end of the line still uses the old foreground color.
Add a space at the end of the line and remove it: it now updates the foreground color of the end of the line to be red too.
Remove //, it only updates the foreground color of the beginning of the line, the end of the line stays red.

In js-mode or for instance emacs-lisp-mode it works fine, the foreground color gets updated immediately on the whole line.

[dgutov]

Hi!

Thanks for the report.

By "red foreground", you mean the foreground of the comment face? If so, I see it.

This might be a fundamental limitation in how font-lock's font-lock-face mapping works. Or it might just require the js2-mode parser to be triggered from syntax-propertize-function. IOW, I see no quick fixes for now.