magit-diff-buffer-file-popup: new command

Documentation/RelNotes/2.5.1.txt

@@ -7,6 +7,10 @@ Updates since v2.5.0
 * Added a cache, which memorizes the values of some function calls for
   the duration of a refresh.  This cuts the calls to git in half.
 
+* Added new command `magit-diff-buffer-file-popup' intended for use in
+  file-visiting buffers.  It shows the same popup as `magit-diff-popup'
+  but starts out already limited to the visited file.
+
 * Added new command `magit-push-refspecs', which allows pushing using
   one or more comma-separated and refspecs, which are explicitly typed
   in the minibuffer.

lisp/magit-diff.el

@@ -556,6 +556,24 @@ and https://debbugs.gnu.org/cgi/bugreport.cgi?bug=7847."
            (default-value 'magit-diff-arguments))))
     (magit-invoke-popup 'magit-diff-popup nil arg)))
 
+(defun magit-diff-buffer-file-popup (arg)
+  "Popup console for diff commans.
+
+This is a variant of `magit-diff-popup' which shows the same popup
+but which limits the diff to the file being visited in the current
+buffer."
+  (interactive "P")
+  (-if-let (file (magit-file-relative-name))
+      (let ((magit-diff-arguments
+             (magit-popup-import-file-args
+              (-if-let (buffer (magit-mode-get-buffer 'magit-diff-mode))
+                  (with-current-buffer buffer
+                    (nth 2 magit-refresh-args))
+                (default-value 'magit-diff-arguments))
+              (list file))))
+        (magit-invoke-popup 'magit-diff-popup nil arg))
+    (user-error "Buffer isn't visiting a file")))
+
 (defun magit-diff-refresh-popup (arg)
   "Popup console for changing diff arguments in the current buffer."
   (interactive "P")

lisp/magit.el

@@ -2262,12 +2262,13 @@ the current repository."
 
 (magit-define-popup magit-file-popup
   "Popup console for Magit commands in file-visiting buffers."
-  :actions '((?s "Stage"   magit-stage-file)
-             (?l "Log"     magit-log-buffer-file)
-             (?c "Commit"  magit-commit-popup)
-             (?u "Unstage" magit-unstage-file)
-             (?b "Blame"   magit-blame-popup) nil nil
-             (?p "Find blob" magit-blob-previous))
+  :actions '((?s "Stage"     magit-stage-file)
+             (?d "Diff"      magit-diff-buffer-file-popup)
+             (?b "Blame"     magit-blame-popup)
+             (?u "Unstage"   magit-unstage-file)
+             (?l "Log"       magit-log-buffer-file)
+             (?p "Find blob" magit-blob-previous)
+             (?c "Commit"    magit-commit-popup))
   :max-action-columns 3)
 
 (defvar magit-file-mode-lighter "")