occur: Add bindings for next-error-no-select

Make the navigation in the occur buffer closer
to the navigation in the compilation buffer.

Add bindings to navigate the occur matches (Bug#39121).
Honor `next-error-highlight' and `next-error-highlight-no-select'
when navigating the occurrences.

* lisp/replace.el (occur-highlight-regexp, occur-highlight-overlay):
New variables.
(occur-1): Set `occur-highlight-regexp' to the searched regexp.
(occur-goto-locus-delete-o, occur--highlight-occurrence): New defuns.
(occur-mode-display-occurrence, occur-mode-goto-occurrence):
Use `occur--highlight-occurrence'.
(occur-mode-map): Bind n to `next-error-no-select'
and p to `previous-error-no-select'

* etc/NEWS (Changes in Specialized Modes and Packages in Emacs 28.1):
Announce this change.

* test/lisp/replace-tests.el (replace-tests-with-highlighted-occurrence):
Add helper macro.
(occur-highlight-occurrence): Add test.

3 files changed, 116 insertions, 1 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 64cf0abbdb4..3086ffaf91b 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -109,6 +109,9 @@ setting the variable 'auto-save-visited-mode' buffer-locally to nil.
 
 * Changes in Specialized Modes and Packages in Emacs 28.1
 
+** New bindings in occur-mode, 'next-error-no-select' bound to 'n' and
+'previous-error-no-select' bound to 'p'.
+
 ** EIEIO: 'oset' and 'oset-default' are declared obsolete.
 
 ** New minor mode 'cl-font-lock-built-in-mode' for `lisp-mode'.
diff --git a/lisp/replace.el b/lisp/replace.el
index f3a71f87fec..69092c16f96 100644
--- a/lisp/replace.el
+++ b/lisp/replace.el
@@ -757,6 +757,13 @@ which will run faster and will not set the mark or print anything."
 Maximum length of the history list is determined by the value
 of `history-length', which see.")
 
+(defvar occur-highlight-regexp t
+  "Regexp matching part of visited source lines to highlight temporarily.
+Highlight entire line if t; don't highlight source lines if nil.")
+
+(defvar occur-highlight-overlay nil
+  "Overlay used to temporarily highlight occur matches.")
+
 (defvar occur-collect-regexp-history '("\\1")
   "History of regexp for occur's collect operation")
 
@@ -1113,6 +1120,8 @@ a previously found match."
     (define-key map "\C-m" 'occur-mode-goto-occurrence)
     (define-key map "o" 'occur-mode-goto-occurrence-other-window)
     (define-key map "\C-o" 'occur-mode-display-occurrence)
+    (define-key map "n" 'next-error-no-select)
+    (define-key map "p" 'previous-error-no-select)
     (define-key map "\M-n" 'occur-next)
     (define-key map "\M-p" 'occur-prev)
     (define-key map "r" 'occur-rename-buffer)
@@ -1261,9 +1270,12 @@ If not invoked by a mouse click, go to occurrence on the current line."
            (with-current-buffer (window-buffer (posn-window (event-end event)))
              (save-excursion
                (goto-char (posn-point (event-end event)))
-               (occur-mode-find-occurrence))))))
+               (occur-mode-find-occurrence)))))
+        (regexp occur-highlight-regexp))
     (pop-to-buffer (marker-buffer pos))
     (goto-char pos)
+    (let ((end-mk (save-excursion (re-search-forward regexp nil t))))
+      (occur--highlight-occurrence pos end-mk))
     (when buffer (next-error-found buffer (current-buffer)))
     (run-hooks 'occur-mode-find-occurrence-hook)))
 
@@ -1277,17 +1289,74 @@ If not invoked by a mouse click, go to occurrence on the current line."
     (next-error-found buffer (current-buffer))
     (run-hooks 'occur-mode-find-occurrence-hook)))
 
+;; Stolen from compile.el
+(defun occur-goto-locus-delete-o ()
+  (delete-overlay occur-highlight-overlay)
+  ;; Get rid of timer and hook that would try to do this again.
+  (if (timerp next-error-highlight-timer)
+      (cancel-timer next-error-highlight-timer))
+  (remove-hook 'pre-command-hook
+               #'occur-goto-locus-delete-o))
+
+;; Highlight the current visited occurrence.
+;; Adapted from `compilation-goto-locus'.
+(defun occur--highlight-occurrence (mk end-mk)
+  (let ((highlight-regexp occur-highlight-regexp))
+    (if (timerp next-error-highlight-timer)
+        (cancel-timer next-error-highlight-timer))
+    (unless occur-highlight-overlay
+      (setq occur-highlight-overlay
+            (make-overlay (point-min) (point-min)))
+      (overlay-put occur-highlight-overlay 'face 'next-error))
+    (with-current-buffer (marker-buffer mk)
+      (save-excursion
+        (if end-mk (goto-char end-mk) (end-of-line))
+        (let ((end (point)))
+          (if mk (goto-char mk) (beginning-of-line))
+          (if (and (stringp highlight-regexp)
+                   (re-search-forward highlight-regexp end t))
+              (progn
+                (goto-char (match-beginning 0))
+                (move-overlay occur-highlight-overlay
+                              (match-beginning 0) (match-end 0)
+                              (current-buffer)))
+            (move-overlay occur-highlight-overlay
+                          (point) end (current-buffer)))
+          (if (or (eq next-error-highlight t)
+                  (numberp next-error-highlight))
+              ;; We want highlighting: delete overlay on next input.
+              (add-hook 'pre-command-hook
+                        #'occur-goto-locus-delete-o)
+            ;; We don't want highlighting: delete overlay now.
+            (delete-overlay occur-highlight-overlay))
+          ;; We want highlighting for a limited time:
+          ;; set up a timer to delete it.
+          (when (numberp next-error-highlight)
+            (setq next-error-highlight-timer
+                  (run-at-time next-error-highlight nil
+                               'occur-goto-locus-delete-o))))))
+    (when (eq next-error-highlight 'fringe-arrow)
+      ;; We want a fringe arrow (instead of highlighting).
+      (setq next-error-overlay-arrow-position
+            (copy-marker (line-beginning-position))))))
+
 (defun occur-mode-display-occurrence ()
   "Display in another window the occurrence the current line describes."
   (interactive)
   (let ((buffer (current-buffer))
         (pos (occur-mode-find-occurrence))
+        (regexp occur-highlight-regexp)
+        (next-error-highlight next-error-highlight-no-select)
+        (display-buffer-overriding-action
+         '(nil (inhibit-same-window . t)))
         window)
     (setq window (display-buffer (marker-buffer pos) t))
     ;; This is the way to set point in the proper window.
     (save-selected-window
       (select-window window)
       (goto-char pos)
+      (let ((end-mk (save-excursion (re-search-forward regexp nil t))))
+        (occur--highlight-occurrence pos end-mk))
       (next-error-found buffer (current-buffer))
       (run-hooks 'occur-mode-find-occurrence-hook))))
 
@@ -1612,6 +1681,7 @@ See also `multi-occur'."
             (buffer-undo-list t)
             (occur--final-pos nil))
         (erase-buffer)
+        (set (make-local-variable 'occur-highlight-regexp) regexp)
         (let ((count
                (if (stringp nlines)
                    ;; Treat nlines as a regexp to collect.
diff --git a/test/lisp/replace-tests.el b/test/lisp/replace-tests.el
index f5cff92d546..aed14c33572 100644
--- a/test/lisp/replace-tests.el
+++ b/test/lisp/replace-tests.el
@@ -546,4 +546,46 @@ Return the last evalled form in BODY."
       ?q
       (string= expected (buffer-string))))))
 
+(defmacro replace-tests-with-highlighted-occurrence (highlight-locus &rest body)
+  "Helper macro to test the highlight of matches when navigating occur buffer.
+
+Eval BODY with `next-error-highlight' and `next-error-highlight-no-select'
+bound to HIGHLIGHT-LOCUS."
+  (declare (indent 1) (debug (form body)))
+  `(let ((regexp "foo")
+         (next-error-highlight ,highlight-locus)
+         (next-error-highlight-no-select ,highlight-locus)
+         (buffer (generate-new-buffer "test"))
+         (inhibit-message t))
+     (unwind-protect
+         ;; Local bind to disable the deletion of `occur-highlight-overlay'
+         (cl-letf (((symbol-function 'occur-goto-locus-delete-o) (lambda ())))
+           (with-current-buffer buffer (dotimes (_ 3) (insert regexp ?\n)))
+           (pop-to-buffer buffer)
+           (occur regexp)
+           (pop-to-buffer "*Occur*")
+           (occur-next)
+           ,@body)
+       (kill-buffer buffer)
+       (kill-buffer "*Occur*"))))
+
+(ert-deftest occur-highlight-occurrence ()
+  "Test for https://debbugs.gnu.org/39121 ."
+  (let ((alist '((nil . nil) (0.5 . t) (t . t) (fringe-arrow . nil)))
+        (check-overlays
+         (lambda (has-ov)
+           (eq has-ov (not (null (overlays-in (point-min) (point-max))))))))
+    (pcase-dolist (`(,highlight-locus . ,has-overlay) alist)
+      ;; Visiting occurrences
+      (replace-tests-with-highlighted-occurrence highlight-locus
+        (occur-mode-goto-occurrence)
+        (should (funcall check-overlays has-overlay)))
+      ;; Displaying occurrences
+      (replace-tests-with-highlighted-occurrence highlight-locus
+        (occur-mode-display-occurrence)
+        (with-current-buffer (marker-buffer
+                              (get-text-property (point) 'occur-target))
+          (should (funcall check-overlays has-overlay)))))))
+
+
 ;;; replace-tests.el ends here