bug#14015: Feature request: highlight partial matches in Info's index-search

[Juri Linkov]

>> +(defcustom Info-index-match-face 'match
>> +  "Face used by \\[Info-index] to show the text that matches.
>> +If the value is nil, don't highlight the matching portions specially."
>> +  :type 'face
>> +  :group 'info
>> +  :version "24.4")
>
> Nowadays, we usually prefer to define a new face that inherits from
> `match'.

I installed with defface that inherits from `match' instead of using defcustom.
All other Info faces are defined with defface too, so a new defface will be
consistent with other Info faces.

However, a new face `list-matching-lines-prefix-face' that I proposed
in bug#14017 is better to define with defcustom for consistency with other
occur-related faces `list-matching-lines-buffer-name-face' and
`list-matching-lines-face' that are defined with defcustom:

  (defcustom list-matching-lines-face 'match
    "Face used by \\[list-matching-lines] to show the text that matches.
  If the value is nil, don't highlight the matching portions specially."
    :type 'face
    :group 'matching)

  (defcustom list-matching-lines-buffer-name-face 'underline
    "Face used by \\[list-matching-lines] to show the names of buffers.
  If the value is nil, don't highlight the buffer names specially."
    :type 'face
    :group 'matching)

I'm not sure whether they should be turned info defface as well
because this will also require converting more related faces to defface,
e.g. grep faces:

  (defvar grep-match-face       'match
    "Face name to use for grep matches.")

  (defvar grep-context-face 'shadow
    "Face name to use for grep context lines.")

And even after adding deffaces for them these old variables should still remain
for backward compatibility with definitions like:

  (defcustom list-matching-lines-face 'occur-match

  (defvar grep-match-face 'grep-match