Allow global VC ops like `C-x v D' in Diff and Log-View buffers.

* vc/diff-mode.el (diff-vc-backend): New var.

* vc/vc.el (vc-deduce-backend): New fun.  Handle diff buffers.
(vc-root-diff, vc-print-root-log, vc-log-incoming)
(vc-log-outgoing): Use it.
(vc-diff-internal): Set diff-vc-backend.

1 files changed, 3 insertions, 0 deletions

diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index adc5a2a0455..0ef9d06c3b2 100644
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -97,6 +97,9 @@ when editing big diffs)."
   :options '(diff-delete-empty-files diff-make-unified)
   :group 'diff-mode)
 
+(defvar diff-vc-backend nil
+  "The VC backend that created the current Diff buffer, if any.")
+
 (defvar diff-outline-regexp
   "\\([*+][*+][*+] [^0-9]\\|@@ ...\\|\\*\\*\\* [0-9].\\|--- [0-9]..\\)")