Subject: bug#52349: 29.0.50; vc-git and diff-mode: stage hunks

From: Juri Linkov <[email-masked]>
Date: Sat, 12 Feb 2022 21:42:50 +0200

> But could you explain the case when the changes to 'vc-diff-internal' are
> going to be used? If those are only for log-edit-show-diff, I think it'd be
> better if the new logic was implemented in the new value of
> log-edit-diff-function, rather than having it spliced into the common code
> path. Would that result in a lot of code duplication?

Not much code duplication, thanks for the suggestion, the patch below
sets log-edit-diff-function for log-edit-show-diff.

> It might also be worth it to thread the 'patch-buffer' value through the
> backend method arguments (the actual value will be the patch string), so
> that vc-git-checkin gets it in the 4th argument, rather than having it call
> (derived-mode-p 'diff-mode) (this feels a little brittle: I suppose which
> buffer is current during this call might change in the future). It would
> also automatically weed out backends which don't support this feature,
> rather than having an attempt to commit from a diff buffer using Hg fail
> silently.

I agree that in the first version ‘(derived-mode-p 'diff-mode)’ was brittle.
But changing the established API with a new argument doesn't look right.
So the next version below uses the buffer-local variable ‘vc-patch-string’.
In other backends such as Hg it shouldn't fail silently, but it will be
just less granular, and will commit whole files instead of edited diffs.

There is a new problem however.  After starting vc-log-edit from *vc-diff*,
and using log-edit-show-diff, it reuses the original buffer *vc-diff*.
This is not a problem, because the buffer-local variable ‘vc-patch-string’
is saved in the *vc-log* buffer.  But after deleting *vc-diff*, log-edit-done
fails on the deleted vc-parent-buffer with

  Debugger entered--Lisp error: (error "Selecting deleted buffer")
    vc-finish-logentry()
    funcall-interactively(vc-finish-logentry)
    log-edit-done()

But this is an old problem.  The same error is signaled
after typing ‘v’ in *vc-dir* buffer, then deleting the
original *vc-dir* buffer, and trying to type ‘C-c C-c’
(log-edit-done) in the *vc-log* buffer.

diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index 0bf7899246..50f68bef70 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -2859,6 +2859,15 @@ diff-syntax-fontify-props
         (forward-line 1)))
     (nreverse props)))
 
+;;;###autoload
+(defun diff-vc-deduce-fileset ()
+  (let ((backend (vc-responsible-backend default-directory))
+        files)
+    (save-excursion
+      (goto-char (point-min))
+      (while (progn (diff-file-next) (not (eobp)))
+        (push (diff-find-file-name nil t) files)))
+    (list backend (nreverse files) nil nil 'patch)))
 
 (defun diff--filter-substring (str)
   (when diff-font-lock-prettify
diff --git a/lisp/vc/vc-dispatcher.el b/lisp/vc/vc-dispatcher.el
index 5c664d58f1..dc141fd650 100644
--- a/lisp/vc/vc-dispatcher.el
+++ b/lisp/vc/vc-dispatcher.el
@@ -653,9 +653,14 @@ vc-log-edit
                      (mapcar
                       (lambda (file) (file-relative-name file root))
                       ',fileset))))
-	      (log-edit-diff-function . vc-diff)
+	      (log-edit-diff-function
+               . ,(if (buffer-local-value 'vc-patch-buffer vc-parent-buffer)
+                      'vc-diff-patch 'vc-diff))
 	      (log-edit-vc-backend . ,backend)
-	      (vc-log-fileset . ,fileset))
+	      (vc-log-fileset . ,fileset)
+              ,@(if (buffer-local-value 'vc-patch-buffer vc-parent-buffer)
+                    `((vc-patch-string . ,(with-current-buffer vc-parent-buffer
+                                            (buffer-string))))))
 	    nil
 	    mode)
   (set-buffer-modified-p nil)
@@ -753,7 +758,8 @@ vc-finish-logentry
 (defun vc-dispatcher-browsing ()
   "Are we in a directory browser buffer?"
   (or (derived-mode-p 'vc-dir-mode)
-      (derived-mode-p 'dired-mode)))
+      (derived-mode-p 'dired-mode)
+      (derived-mode-p 'diff-mode)))
 
 ;; These are unused.
 ;; (defun vc-dispatcher-in-fileset-p (fileset)
diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index 208cbee0e6..4eb114633d 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -943,12 +943,20 @@ vc-git-checkin
           (if (eq system-type 'windows-nt)
               (let ((default-directory (file-name-directory file1)))
                 (make-nearby-temp-file "git-msg")))))
+    (when vc-patch-string
+      (let ((patch-file (make-temp-file "git-patch")))
+        (with-temp-file patch-file
+          (insert vc-patch-string))
+        (unwind-protect
+            (apply #'vc-git-command nil 0 patch-file
+                   (list "apply" "--cached"))
+          (delete-file patch-file))))
     (cl-flet ((boolean-arg-fn
                (argument)
                (lambda (value) (when (equal value "yes") (list argument)))))
       ;; When operating on the whole tree, better pass "-a" than ".", since "."
       ;; fails when we're committing a merge.
-      (apply #'vc-git-command nil 0 (if only files)
+      (apply #'vc-git-command nil 0 (if (and only (not vc-patch-string)) files)
              (nconc (if msg-file (list "commit" "-F"
                                        (file-local-name msg-file))
                       (list "commit" "-m"))
@@ -966,7 +974,8 @@ vc-git-checkin
                           (write-region (car args) nil msg-file))
                         (setq args (cdr args)))
                       args)
-		    (if only (list "--only" "--") '("-a")))))
+                    (unless vc-patch-string
+                      (if only (list "--only" "--") '("-a"))))))
     (if (and msg-file (file-exists-p msg-file)) (delete-file msg-file))))
 
 (defun vc-git-find-revision (file rev buffer)
diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index a6124acadd..1b30e9b671 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -1102,6 +1102,8 @@ vc-deduce-fileset-1
       (vc-dir-deduce-fileset state-model-only-files))
      ((derived-mode-p 'dired-mode)
       (dired-vc-deduce-fileset state-model-only-files not-state-changing))
+     ((derived-mode-p 'diff-mode)
+      (diff-vc-deduce-fileset))
      ((setq backend (vc-backend buffer-file-name))
       (if state-model-only-files
 	(list backend (list buffer-file-name)
@@ -1114,7 +1116,8 @@ vc-deduce-fileset-1
            (or (buffer-file-name vc-parent-buffer)
 				(with-current-buffer vc-parent-buffer
 				  (or (derived-mode-p 'vc-dir-mode)
-				      (derived-mode-p 'dired-mode)))))
+				      (derived-mode-p 'dired-mode)
+				      (derived-mode-p 'diff-mode)))))
       (progn                  ;FIXME: Why not `with-current-buffer'? --Stef.
 	(set-buffer vc-parent-buffer)
 	(vc-deduce-fileset-1 not-state-changing allow-unregistered state-model-only-files)))
@@ -1230,6 +1233,9 @@ vc-next-action
       (error "Fileset files are missing, so cannot be operated on"))
      ((eq state 'ignored)
       (error "Fileset files are ignored by the version-control system"))
+     ((eq model 'patch)
+      (setq-local vc-patch-buffer t)
+      (vc-checkin files backend))
      ((or (null state) (eq state 'unregistered))
       (cond (verbose
              (let ((backend (vc-read-backend "Backend to register to: ")))
@@ -1779,6 +1785,24 @@ vc-diff-finish
 (defvar vc-diff-added-files nil
   "If non-nil, diff added files by comparing them to /dev/null.")
 
+(defvar vc-patch-buffer nil)
+(defvar vc-patch-string nil)
+
+(defun vc-diff-patch ()
+  (let ((buffer "*vc-diff*")
+        (patch-string vc-patch-string))
+    (vc-setup-buffer buffer)
+    (set-buffer buffer)
+    (let ((buffer-undo-list t)
+          (inhibit-read-only t))
+      (insert patch-string))
+    (setq buffer-read-only t)
+    (diff-mode)
+    (setq-local diff-vc-backend (vc-responsible-backend default-directory))
+    (setq-local revert-buffer-function (lambda (_ _) (vc-diff-patch)))
+    (pop-to-buffer (current-buffer))
+    (vc-run-delayed (vc-diff-finish (current-buffer) nil))))
+
 (defun vc-diff-internal (async vc-fileset rev1 rev2 &optional verbose buffer)
   "Report diffs between two revisions of a fileset.
 Output goes to the buffer BUFFER, which defaults to *vc-diff*.