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

[Juri Linkov]

> When 'i foo RET' yields a partial match, e.g., finding "foobar" in the
> index, the stand-alone Info reader "highlights" the part that matched,
> like this:
>
>    Found FOObar in Some Node. (`,' tries to find next.)
>
> (The stand-alone reader is a text-mode program, so it changes the
> letter-case to emphasize the part that matched.)
>
> It would be nice if Emacs did something similar, although it is
> probably better to use colors if available.

info-look.el uses the following face to highlight found matches
in the Info reader:

  (defcustom info-lookup-highlight-face 'match
    "Face for highlighting looked up help items.
  Setting this variable to nil disables highlighting."
    :group 'info-lookup :type 'face)

Adding a similar face option to highlight the text matched by `Info-index'
will change the output of `Info-virtual-index' and `info-apropos'
to look exactly the same like as output of `occur' that is good
for consistency of the UI.  This is in addition to highlighting
the matches in the each area that you asked for:

=== modified file 'lisp/info.el'
--- lisp/info.el        2013-03-20 23:04:40 +0000
+++ lisp/info.el        2013-03-21 22:30:34 +0000
@@ -158,6 +158,13 @@ (defface info-header-node
   "Face for Info nodes in a node header."
   :group 'info)
 
+(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")
+
 ;; This is a defcustom largely so that we can get the benefit
 ;; of custom-initialize-delay.  Perhaps it would work to make it a
 ;; defvar and explicitly give it a standard-value property, and
@@ -3295,12 +3302,14 @@ (defun Info-index (topic)
              (progn
                (goto-char (point-min))
                (while (re-search-forward pattern nil t)
-                 (push (list (match-string-no-properties 1)
-                             (match-string-no-properties 2)
-                             Info-current-node
-                             (string-to-number (concat "0"
-                                                       (match-string 3))))
-                       matches))
+                 (let ((entry (match-string-no-properties 1))
+                       (nodename (match-string-no-properties 2))
+                       (line (string-to-number (concat "0" (match-string 3)))))
+                   (when (and Info-index-match-face
+                              (string-match (regexp-quote topic) entry))
+                     (add-text-properties (match-beginning 0) (match-end 0)
+                                          `(face ,Info-index-match-face) 
entry))
+                   (push (list entry nodename Info-current-node line) 
matches)))
                (setq nodes (cdr nodes) node (car nodes)))
            (Info-goto-node node))
          (or matches
@@ -3559,12 +3568,15 @@ (defun Info-apropos-matches (string)
                         (progn
                           (goto-char (point-min))
                           (while (re-search-forward pattern nil t)
-                           (setq matches
-                                 (cons (list manual
-                                             (match-string-no-properties 1)
-                                             (match-string-no-properties 2)
-                                             (match-string-no-properties 3))
-                                       matches)))
+                           (let ((entry (match-string-no-properties 1))
+                                 (nodename (match-string-no-properties 2))
+                                 (line (match-string-no-properties 3)))
+                             (when (and Info-index-match-face
+                                        (string-match (regexp-quote string) 
entry))
+                               (add-text-properties (match-beginning 0) 
(match-end 0)
+                                                    `(face 
,Info-index-match-face) entry))
+                             (setq matches (cons (list manual entry nodename 
line)
+                                                 matches))))
                           (setq nodes (cdr nodes) node (car nodes)))
                       (Info-goto-node node))))
            (error