bug#15298: 24.3.50; Background color lost when highlighting a string

[Glenn Morris]

Minimal example:

(defface foo '((t :foreground "blue" :background "yellow"))
  "foo face")

(define-derived-mode foo-mode nil "foo"
  "foo doc"
  (set (make-local-variable 'font-lock-defaults)
       '((("^FOO.*" . 'foo)))))

(font-lock-add-keywords 'foo-mode '(("bar" 0 'underline prepend)))

Eval that, M-x foo-mode, enter

FOO text bar text

As soon as "bar" is entered, "FOO..." loses its highlighting.


It works if you use instead:

(font-lock-add-keywords 'foo-mode '(("bar" 0 'underline prepend)) 'end)


Another approach that works is:

(define-derived-mode foo-mode nil "foo"
  "foo doc"
  (set (make-local-variable 'font-lock-defaults)
       '((("^FOO.*" 0 'foo append)))))    ; note addition of "append" here

(font-lock-add-keywords 'foo-mode '(("bar" 0 'underline)))


So I think this is not a bug, just a confusing aspect of the way
font-lock-keywords is applied in order.