From: Juri Linkov <juri@linkov.net>
Date: Wed, 14 Nov 2018 00:23:04 +0000 (+0200)
Subject: New option vc-find-revision-no-save to not write revision to file
X-Git-Tag: emacs-27.0.90~4165
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=f561c6a1124d4a1d79c264a9cb79ac0e7cb1650f;p=emacs.git

New option vc-find-revision-no-save to not write revision to file

* lisp/vc/vc.el (vc-find-revision-no-save): New defcustom (bug#33319).
(vc-find-revision): Depending on vc-find-revision-no-save,
call either vc-find-revision-no-save or vc-find-revision-save.
(vc-find-revision-save): Rename from vc-find-revision.
(vc-find-revision-no-save): New function.

* lisp/vc/diff-mode.el (diff-find-source-location):
Let-bind vc-find-revision-no-save to t.
---

diff --git a/etc/NEWS b/etc/NEWS
index 2a2010e9d36..44f54894cdb 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -344,6 +344,9 @@ still be used if it exists.)  Set the variable to nil to get the
 previous behavior of always creating a buffer that visits a ChangeLog
 file.
 
+*** New customizable variable 'vc-find-revision-no-save'.
+With non-nil, 'vc-find-revision' doesn't write the created buffer to file.
+
 *** New customizable variable 'vc-git-grep-template'.
 This new variable allows customizing the default arguments passed to
 git-grep when 'vc-git-grep' is used.
diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index 8539423eed5..b86c17fe366 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -56,6 +56,7 @@
 (eval-when-compile (require 'cl-lib))
 
 (autoload 'vc-find-revision "vc")
+(defvar vc-find-revision-no-save)
 (defvar add-log-buffer-file-name-function)
 
 
@@ -1743,7 +1744,8 @@ NOPROMPT, if non-nil, means not to prompt the user."
 	   (revision (and other diff-vc-backend
                           (nth (if reverse 1 0) diff-vc-revisions)))
 	   (buf (if revision
-                    (vc-find-revision file revision diff-vc-backend)
+                    (let ((vc-find-revision-no-save t))
+                      (vc-find-revision file revision diff-vc-backend))
                   (find-file-noselect file))))
       ;; Update the user preference if he so wished.
       (when (> (prefix-numeric-value other-file) 8)
diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 6b7ca02440d..de43544864f 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -871,6 +871,12 @@ is sensitive to blank lines."
 		       (string :tag "Comment End")))
   :group 'vc)
 
+(defcustom vc-find-revision-no-save nil
+  "If non-nil, `vc-find-revision' doesn't write the created buffer to file."
+  :type 'boolean
+  :group 'vc
+  :version "27.1")
+
 
 ;; File property caching
 
@@ -1953,6 +1959,13 @@ If `F.~REV~' already exists, use it instead of checking it out again."
 (defun vc-find-revision (file revision &optional backend)
   "Read REVISION of FILE into a buffer and return the buffer.
 Use BACKEND as the VC backend if specified."
+  (if vc-find-revision-no-save
+      (vc-find-revision-no-save file revision backend)
+    (vc-find-revision-save file revision backend)))
+
+(defun vc-find-revision-save (file revision &optional backend)
+  "Read REVISION of FILE into a buffer and return the buffer.
+Saves the buffer to the file."
   (let ((automatic-backup (vc-version-backup-file-name file revision))
 	(filebuf (or (get-file-buffer file) (current-buffer)))
         (filename (vc-version-backup-file-name file revision 'manual)))
@@ -1985,6 +1998,38 @@ Use BACKEND as the VC backend if specified."
 	(set (make-local-variable 'vc-parent-buffer) filebuf))
       result-buf)))
 
+(defun vc-find-revision-no-save (file revision &optional backend)
+  "Read REVISION of FILE into a buffer and return the buffer.
+Unlike `vc-find-revision-save', doesn't save the created buffer to file."
+  (let ((filebuf (or (get-file-buffer file) (current-buffer)))
+        (filename (vc-version-backup-file-name file revision 'manual)))
+    (unless (or (get-file-buffer filename)
+                (file-exists-p filename))
+      (with-current-buffer filebuf
+	(let ((failed t))
+	  (unwind-protect
+	      (let ((coding-system-for-read 'no-conversion)
+		    (coding-system-for-write 'no-conversion))
+		(with-current-buffer (create-file-buffer filename)
+                  (setq buffer-file-name filename)
+		  (let ((outbuf (current-buffer)))
+		    (with-current-buffer filebuf
+		      (if backend
+			  (vc-call-backend backend 'find-revision file revision outbuf)
+			(vc-call find-revision file revision outbuf))))
+                  (goto-char (point-min))
+                  (normal-mode)
+	          (set-buffer-modified-p nil)
+                  (setq buffer-read-only t))
+		(setq failed nil))
+	    (when (and failed (get-file-buffer filename))
+	      (kill-buffer (get-file-buffer filename)))))))
+    (let ((result-buf (or (get-file-buffer filename)
+                          (find-file-noselect filename))))
+      (with-current-buffer result-buf
+	(set (make-local-variable 'vc-parent-buffer) filebuf))
+      result-buf)))
+
 ;; Header-insertion code
 
 ;;;###autoload