bug#70820: [PATCH] Editable grep buffers

[Visuwesh <visuweshm@gmail.com>]

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Tags: patch

Attached patch is a proof of concept for an occur-edit-mode alike for
*grep* buffers.  It uses the new track-changes library to track the
edits made in the *grep* buffer to then finally save these edits to the
corresponding files.  I've tested this with:

    1. pure deletions: If you have a match that says "(cur-beg start"
       and you change it to "(cur- start".  This is special because
       track-changes-fetch passes equal BEG and END to
       grep-edit--track-changes-finalise.
    2. edits: something like "(cur-beg start" -> "(cur-beg start balh"
       is handled like you would expect.
    3. edits with newline: if the edit includes a newline, then that is
       reproduced.

and what is not handled currently: deleting a match line to imply
deletion of that line from the matched file.  I don't know how to handle
this currently, I need to learn the library more.

There's also definitely a million more cases that I didn't anticipate
when I wrote the logic for grep-edit--track-changes-finalise.

I'm sending the patch now to see if there's enough interest before I go
about fixing the edge cases (there's bug#52815).  If there is enough
interest, I will take a shot at implementing something like this for
xref result buffers too.



In GNU Emacs 30.0.50 (build 8, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.18.0, Xaw scroll bars) of 2024-05-07 built on astatine
Repository revision: 4b31074f5f49898ba0499a2b617cad425750eafa
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101011
System Description: Debian GNU/Linux trixie/sid

Configured using:
 'configure --with-sound=alsa --with-x-toolkit=lucid --with-json
 --without-xaw3d --without-gconf --without-libsystemd --with-cairo
 --with-xft'

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diff --git a/lisp/progmodes/grep.el b/lisp/progmodes/grep.el
index 657349cbdff..3fa6fce0e8d 100644
--- a/lisp/progmodes/grep.el
+++ b/lisp/progmodes/grep.el
@@ -31,6 +31,7 @@
 
 (eval-when-compile (require 'cl-lib))
 (require 'compile)
+(require 'track-changes)
 
 (defgroup grep nil
   "Run `grep' and display the results."
@@ -295,6 +296,8 @@ grep-mode-map
     (define-key map "}" #'compilation-next-file)
     (define-key map "\t" #'compilation-next-error)
     (define-key map [backtab] #'compilation-previous-error)
+
+    (define-key map "e" #'grep-edit-minor-mode)
     map)
   "Keymap for grep buffers.
 `compilation-minor-mode-map' is a cdr of this.")
@@ -1029,6 +1032,71 @@ grep
 		       command-args)
 		     #'grep-mode))
 
+(defvar-local grep-edit--tracker nil
+  "ID of the `track-changes' tracker.")
+
+(defun grep-edit--track-changes-signal (_id &optional _distance)
+  ;; Empty because we want to simply accumulate the changes at end
+  ;; when the user calls the finish function.
+  nil)
+
+(defun grep-edit--track-changes-finalise (beg end _before)
+  (let ((grep-buf (current-buffer))
+        (cur-res beg))                  ; Point at current grep result.
+    (save-excursion
+      (while (<= cur-res end)
+        (goto-char cur-res)
+        (let* ((change-beg (next-single-char-property-change (pos-bol) 'compilation-message))
+               ;; `1-' is required to ignore the newline.
+               (change-end (1- (next-single-char-property-change (pos-eol) 'compilation-message)))
+               (loc (compilation--message->loc
+                     (get-text-property (pos-bol) 'compilation-message)))
+               (line (compilation--loc->line loc))
+               (file (caar (compilation--loc->file-struct loc))))
+          (with-current-buffer (find-file-noselect file)
+            (save-excursion
+              (goto-char (point-min))
+              (forward-line (1- line))
+              (delete-region (pos-bol) (pos-eol))
+              (insert-buffer-substring-no-properties grep-buf change-beg change-end))))
+        (setq cur-res  (next-single-property-change cur-res 'compilation-message))))))
+
+(define-minor-mode grep-edit-minor-mode
+  "Minor mode for editing *grep* buffers.
+In this mode, changes to the *grep* buffer are applied to the
+originating files upon saving using \\[grep-save-changes]."
+  :lighter " Grep-Edit"
+  (if (null grep-edit-minor-mode)
+      (progn
+        (setq buffer-read-only t)
+        (buffer-disable-undo)
+        (use-local-map grep-mode-map))
+    (unless grep-edit--tracker
+      (use-local-map grep-edit-minor-mode-map)
+      (setq buffer-read-only nil)
+      (buffer-enable-undo)
+      (setq grep-edit--tracker
+            (track-changes-register #'grep-edit--track-changes-signal
+                                    :disjoint t)))
+    (message (substitute-command-keys
+              "Editing: \\[grep-edit-save-changes] to return to Grep mode."))))
+
+(defun grep-edit-save-changes ()
+  "Save the changes made to the *grep* buffer."
+  (interactive)
+  (when (and grep-edit-minor-mode grep-edit--tracker)
+    (track-changes-fetch grep-edit--tracker #'grep-edit--track-changes-finalise)
+    (message "Applied edits, switching to Grep mode.")
+    (track-changes-unregister grep-edit--tracker)
+    (setq grep-edit--tracker nil)
+    (grep-edit-minor-mode -1)))
+
+(defvar grep-edit-minor-mode-map
+  (let ((map (make-sparse-keymap)))
+    (set-keymap-parent map text-mode-map)
+    (define-key map (kbd "C-c C-c") #'grep-edit-save-changes)
+    map)
+  "Keymap for `grep-edit-minor-mode'.")
 
 ;;;###autoload
 (defun grep-find (command-args)