Show current line highlighted in *Occur* buffer

* lisp/replace.el (list-matching-lines-current-line-face)
(list-matching-lines-jump-to-current-line): New user options.
(occur--orig-line, occur--orig-line-str): New variables.
(occur, occur-engine): Use them.
(occur--final-pos): New variable.
(occur-1): Use it.
(occur-engine): Idem.
Show the current line with 'list-matching-lines-current-line-face'.
Set point on the first matching line after the current one.
* etc/NEWS: Add entry for the new option.

3 files changed, 76 insertions, 5 deletions

diff --git a/doc/emacs/search.texi b/doc/emacs/search.texi
index 2a67619678b..a6cb1a4c9f5 100644
--- a/doc/emacs/search.texi
+++ b/doc/emacs/search.texi
@@ -1726,6 +1726,10 @@ face.  A numeric argument @var{n} specifies that @var{n} lines of
 context are to be displayed before and after each matching line.
 The default number of context lines is specified by the variable
 @code{list-matching-lines-default-context-lines}.
+When @code{list-matching-lines-jump-to-current-line} is non-nil,
+the current line is shown highlighted with face
+@code{list-matching-lines-current-line-face} and the point is set
+at the first match after such line.
 
 You can also run @kbd{M-s o} when an incremental search is active;
 this uses the current search string.
diff --git a/etc/NEWS b/etc/NEWS
index dcefb75fd55..ddd40fa8535 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -311,6 +311,11 @@ substituted by a home directory by writing it as "/foo:/:/~/file".
 * Editing Changes in Emacs 26.1
 
 +++
+** Two new user options 'list-matching-lines-jump-to-current-line' and
+'list-matching-lines-current-line-face' to show highlighted the current
+line in *Occur* buffer.
+
++++
 ** The 'occur' command can now operate on the region.
 
 +++
diff --git a/lisp/replace.el b/lisp/replace.el
index 0a8e4804858..a825040a979 100644
--- a/lisp/replace.el
+++ b/lisp/replace.el
@@ -1304,6 +1304,19 @@ If the value is nil, don't highlight the buffer names specially."
   :type 'face
   :group 'matching)
 
+(defcustom list-matching-lines-current-line-face 'lazy-highlight
+  "Face used by \\[list-matching-lines] to highlight the current line."
+  :type 'face
+  :group 'matching
+  :version "26.1")
+
+(defcustom list-matching-lines-jump-to-current-line nil
+  "If non-nil, \\[list-matching-lines] shows the current line highlighted.
+Set the point right after such line when there are matches after it."
+:type 'boolean
+:group 'matching
+:version "26.1")
+
 (defcustom list-matching-lines-prefix-face 'shadow
   "Face used by \\[list-matching-lines] to show the prefix column.
 If the face doesn't differ from the default face,
@@ -1364,6 +1377,9 @@ invoke `occur'."
 (defvar occur--region-start nil)
 (defvar occur--region-end nil)
 (defvar occur--matches-threshold nil)
+(defvar occur--orig-line nil)
+(defvar occur--orig-line-str nil)
+(defvar occur--final-pos nil)
 
 (defun occur (regexp &optional nlines region)
   "Show all lines in the current buffer containing a match for REGEXP.
@@ -1382,6 +1398,9 @@ REGION must be a list of (START . END) positions as returned by
 The lines are shown in a buffer named `*Occur*'.
 It serves as a menu to find any of the occurrences in this buffer.
 \\<occur-mode-map>\\[describe-mode] in that buffer will explain how.
+If `list-matching-lines-jump-to-current-line' is non-nil, then show
+the current line highlighted with `list-matching-lines-current-line-face'
+and set point at the first match after such line.
 
 If REGEXP contains upper case characters (excluding those preceded by `\\')
 and `search-upper-case' is non-nil, the matching is case-sensitive.
@@ -1409,7 +1428,13 @@ is not modified."
           (occur--region-end end)
           (occur--matches-threshold
            (and in-region-p
-                (line-number-at-pos (min start end)))))
+                (line-number-at-pos (min start end))))
+          (occur--orig-line
+           (line-number-at-pos (point)))
+          (occur--orig-line-str
+           (buffer-substring-no-properties
+            (line-beginning-position)
+            (line-end-position))))
       (save-excursion ; If no matches `occur-1' doesn't restore the point.
         (and in-region-p (narrow-to-region start end))
         (occur-1 regexp nlines (list (current-buffer)))
@@ -1508,7 +1533,8 @@ See also `multi-occur'."
         (occur-mode))
       (let ((inhibit-read-only t)
             ;; Don't generate undo entries for creation of the initial contents.
-            (buffer-undo-list t))
+            (buffer-undo-list t)
+            (occur--final-pos nil))
         (erase-buffer)
         (let ((count
                (if (stringp nlines)
@@ -1560,6 +1586,10 @@ See also `multi-occur'."
           (if (= count 0)
               (kill-buffer occur-buf)
             (display-buffer occur-buf)
+            (when occur--final-pos
+              (set-window-point
+               (get-buffer-window occur-buf 'all-frames)
+               occur--final-pos))
             (setq next-error-last-buffer occur-buf)
             (setq buffer-read-only t)
             (set-buffer-modified-p nil)
@@ -1572,7 +1602,8 @@ See also `multi-occur'."
           (global-matches 0)  ;; total count of matches
           (coding nil)
           (case-fold-search case-fold)
-          (in-region-p (and occur--region-start occur--region-end)))
+          (in-region-p (and occur--region-start occur--region-end))
+          (multi-occur-p (cdr buffers)))
       ;; Map over all the buffers
       (dolist (buf buffers)
         (when (buffer-live-p buf)
@@ -1580,12 +1611,16 @@ See also `multi-occur'."
                 (matches 0)             ;; count of matches
                 (curr-line              ;; line count
                  (or occur--matches-threshold 1))
+                (orig-line occur--orig-line)
+                (orig-line-str occur--orig-line-str)
+                (orig-line-shown-p)
                 (prev-line nil)         ;; line number of prev match endpt
                 (prev-after-lines nil)  ;; context lines of prev match
                 (matchbeg 0)
                 (origpt nil)
                 (begpt nil)
                 (endpt nil)
+                (finalpt nil)
                 (marker nil)
                 (curstring "")
                 (ret nil)
@@ -1686,6 +1721,18 @@ See also `multi-occur'."
                               (nth 0 ret))))
                       ;; Actually insert the match display data
                       (with-current-buffer out-buf
+                        (when (and list-matching-lines-jump-to-current-line
+                                   (not multi-occur-p)
+                                   (not orig-line-shown-p)
+                                   (>= curr-line orig-line))
+                          (insert
+                           (concat
+                            (propertize
+                             (format "%7d:%s" orig-line orig-line-str)
+                             'face list-matching-lines-current-line-face
+                             'mouse-face 'mode-line-highlight
+                             'help-echo "Current line") "\n"))
+                          (setq orig-line-shown-p t finalpt (point)))
                         (insert data)))
                     (goto-char endpt))
                   (if endpt
@@ -1699,6 +1746,18 @@ See also `multi-occur'."
                         (forward-line 1))
                     (goto-char (point-max)))
                   (setq prev-line (1- curr-line)))
+                ;; Insert original line if haven't done yet.
+                (when (and list-matching-lines-jump-to-current-line
+                           (not multi-occur-p)
+                           (not orig-line-shown-p))
+                  (with-current-buffer out-buf
+                    (insert
+                     (concat
+                      (propertize
+                       (format "%7d:%s" orig-line orig-line-str)
+                       'face list-matching-lines-current-line-face
+                       'mouse-face 'mode-line-highlight
+                       'help-echo "Current line") "\n"))))
                 ;; Flush remaining context after-lines.
                 (when prev-after-lines
                   (with-current-buffer out-buf
@@ -1732,8 +1791,11 @@ See also `multi-occur'."
                   (setq end (point))
                   (add-text-properties beg end `(occur-title ,buf))
                   (when title-face
-                    (add-face-text-property beg end title-face)))
-                (goto-char (point-min)))))))
+                    (add-face-text-property beg end title-face))
+                  (goto-char (if finalpt
+                                 (setq occur--final-pos
+                                       (cl-incf finalpt (- end beg)))
+                               (point-min)))))))))
       ;; Display total match count and regexp for multi-buffer.
       (when (and (not (zerop global-lines)) (> (length buffers) 1))
         (goto-char (point-min))