* lisp/vc/vc.el (vc-region-history): New command.

(vc-print-log-internal): Use cl-some.
* lisp/vc/vc-git.el (vc-git-region-history): New function.
(vc-git-region-history-mode-map)
(vc-git--log-view-long-font-lock-keywords)
(vc-git-region-history-font-lock-keywords): New vars.
(vc-git-region-history-font-lock): New function.
(vc-git-region-history-mode): New major mode.

4 files changed, 106 insertions, 19 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 6dcf64bede3..68ad5c00c8f 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -125,6 +125,8 @@ Unicode standards.
 
 * Changes in Specialized Modes and Packages in Emacs 25.1
 
+** VC
+*** The new command vc-region-history shows the log+diff of the active region.
 ** Calc
 +++
 *** If `quick-calc' is called with a prefix argument, insert the
diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 9b8cf9793cd..a0108305ac3 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,15 @@
+2014-11-05  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+        * vc/vc.el (vc-region-history): New command.
+        (vc-print-log-internal): Use cl-some.
+
+        * vc/vc-git.el (vc-git-region-history): New function.
+        (vc-git-region-history-mode-map)
+        (vc-git--log-view-long-font-lock-keywords)
+        (vc-git-region-history-font-lock-keywords): New vars.
+        (vc-git-region-history-font-lock): New function.
+        (vc-git-region-history-mode): New major mode.
+
 2014-11-05  Tassilo Horn  <tsdh@gnu.org>
 
         * net/eww.el (subr-x): Require subr-x at compile-time because eww
@@ -23,9 +35,9 @@
 
 2014-11-05  Michael Albinus  <michael.albinus@gmx.de>
 
-        * net/tramp-sh.el (tramp-do-copy-or-rename-file-via-buffer): Don't use
-        a local copy; setting `inhibit-file-name-handlers' proper might be
-        more performant.  (Bug#18751)
+        * net/tramp-sh.el (tramp-do-copy-or-rename-file-via-buffer): Don't use
+        a local copy; setting `inhibit-file-name-handlers' proper might be
+        more performant.  (Bug#18751)
 
 2014-11-05  Glenn Morris  <rgm@gnu.org>
 
diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index afcfd666082..5d7c0ef5c7b 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -869,6 +869,52 @@ If LIMIT is non-nil, show no more than this many entries."
                         "@{upstream}"
                       remote-location))))
 
+(defun vc-git-region-history (file buffer lfrom lto)
+  (vc-git-command buffer 'async nil "log" "-p" ;"--follow" ;FIXME: not supported?
+                  (format "-L%d,%d:%s" lfrom lto (file-relative-name file))))
+
+(require 'diff-mode)
+
+(defvar vc-git-region-history-mode-map
+  (let ((map (make-composed-keymap
+              nil (make-composed-keymap
+                   (list diff-mode-map vc-git-log-view-mode-map)))))
+    map))
+
+(defvar vc-git--log-view-long-font-lock-keywords nil)
+(defvar font-lock-keywords)
+(defvar vc-git-region-history-font-lock-keywords
+  `((vc-git-region-history-font-lock)))
+
+(defun vc-git-region-history-font-lock (limit)
+  (let ((in-diff (save-excursion
+                   (beginning-of-line)
+                   (or (looking-at "^\\(?:diff\\|commit\\)\\>")
+                       (re-search-backward "^\\(?:diff\\|commit\\)\\>" nil t))
+                   (eq ?d (char-after (match-beginning 0))))))
+    (while
+        (let ((end (save-excursion
+                     (if (re-search-forward "\n\\(diff\\|commit\\)\\>"
+                                            limit t)
+                         (match-beginning 1)
+                       limit))))
+          (let ((font-lock-keywords (if in-diff diff-font-lock-keywords
+                                      vc-git--log-view-long-font-lock-keywords)))
+            (font-lock-fontify-keywords-region (point) end))
+          (goto-char end)
+          (prog1 (< (point) limit)
+            (setq in-diff (eq ?d (char-after))))))
+    nil))
+
+(define-derived-mode vc-git-region-history-mode
+    vc-git-log-view-mode "Git-Region-History"
+  "Major mode to browse Git's \"log -p\" output."
+  (setq-local vc-git--log-view-long-font-lock-keywords
+              log-view-font-lock-keywords)
+  (setq-local font-lock-defaults
+              (cons 'vc-git-region-history-font-lock-keywords
+                    (cdr font-lock-defaults))))
+
 (defvar log-view-message-re)
 (defvar log-view-file-re)
 (defvar log-view-font-lock-keywords)
@@ -884,7 +930,7 @@ If LIMIT is non-nil, show no more than this many entries."
        (if (not (eq vc-log-view-type 'long))
            (cadr vc-git-root-log-format)
          "^commit *\\([0-9a-z]+\\)"))
-  ;; Allow expanding short log entries
+  ;; Allow expanding short log entries.
   (when (eq vc-log-view-type 'short)
     (setq truncate-lines t)
     (set (make-local-variable 'log-view-expanded-log-entry-function)
diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 5491d67e700..b2cb4470da1 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -1,4 +1,4 @@
-;;; vc.el --- drive a version-control system from within Emacs  -*- lexical-binding: t -*-
+;;; vc.el --- drive a version-control system from within Emacs  -*- lexical-binding:t -*-
 
 ;; Copyright (C) 1992-1998, 2000-2014 Free Software Foundation, Inc.
 
@@ -458,6 +458,15 @@
 ;;   If the backend supports annotating through copies and renames,
 ;;   and displays a file name and a revision, then return a cons
 ;;   (REVISION . FILENAME).
+;;
+;; - region-history (FILE BUFFER LFROM LTO)
+;;
+;;   Insert into BUFFER the history (log comments and diffs) of the content of
+;;   FILE between lines LFROM and LTO.  This is typically done asynchronously.
+;;
+;; - region-history-mode ()
+;;
+;;   Major mode to use for the output of `region-history'.
 
 ;; TAG SYSTEM
 ;;
@@ -673,6 +682,7 @@
 
 (require 'vc-hooks)
 (require 'vc-dispatcher)
+(require 'cl-lib)
 
 (declare-function diff-setup-whitespace "diff-mode" ())
 
@@ -2227,19 +2237,11 @@ earlier revisions.  Show up to LIMIT entries (non-nil means unlimited)."
   ;; Don't switch to the output buffer before running the command,
   ;; so that any buffer-local settings in the vc-controlled
   ;; buffer can be accessed by the command.
-  (let ((dir-present nil)
-        (vc-short-log nil)
+  (let* ((dir-present (cl-some #'file-directory-p files))
+         (shortlog (not (null (memq (if dir-present 'directory 'file)
+                                    vc-log-short-style))))
         (buffer-name "*vc-change-log*")
-        type)
-    (dolist (file files)
-      (when (file-directory-p file)
-        (setq dir-present t)))
-    (setq vc-short-log
-          (not (null (if dir-present
-                         (memq 'directory vc-log-short-style)
-                       (memq 'file vc-log-short-style)))))
-    (setq type (if vc-short-log 'short 'long))
-    (let ((shortlog vc-short-log))
+         (type (if shortlog 'short 'long)))
       (vc-log-internal-common
        backend buffer-name files type
        (lambda (bk buf _type-arg files-arg)
@@ -2252,7 +2254,7 @@ earlier revisions.  Show up to LIMIT entries (non-nil means unlimited)."
          (vc-call-backend bk 'show-log-entry working-revision))
        (lambda (_ignore-auto _noconfirm)
          (vc-print-log-internal backend files working-revision
-                                is-start-revision limit))))))
+                              is-start-revision limit)))))
 
 (defvar vc-log-view-type nil
   "Set this to differentiate the different types of logs.")
@@ -2271,7 +2273,6 @@ earlier revisions.  Show up to LIMIT entries (non-nil means unlimited)."
     (with-current-buffer (get-buffer-create buffer-name)
       (set (make-local-variable 'vc-log-view-type) type))
     (setq retval (funcall backend-func backend buffer-name type files))
-    (pop-to-buffer buffer-name)
     (let ((inhibit-read-only t))
       ;; log-view-mode used to be called with inhibit-read-only bound
       ;; to t, so let's keep doing it, just in case.
@@ -2280,6 +2281,9 @@ earlier revisions.  Show up to LIMIT entries (non-nil means unlimited)."
       (set (make-local-variable 'log-view-vc-fileset) files)
       (set (make-local-variable 'revert-buffer-function)
            rev-buff-func))
+    ;; Display after setting up major-mode, so display-buffer-alist can know
+    ;; the major-mode.
+    (pop-to-buffer buffer-name)         
     (vc-run-delayed
      (let ((inhibit-read-only t))
        (funcall setup-buttons-func backend files retval)
@@ -2387,6 +2391,29 @@ When called interactively with a prefix argument, prompt for REMOTE-LOCATION."
                                    'log-outgoing)))
 
 ;;;###autoload
+(defun vc-region-history (from to)
+  "Show the history of the region FROM..TO."
+  (interactive "r")
+  (let* ((lfrom (line-number-at-pos from))
+         (lto   (line-number-at-pos to))
+         (file buffer-file-name)
+         (backend (vc-backend file))
+         (buf (get-buffer-create "*VC-history*")))
+    (with-current-buffer buf
+      (setq-local vc-log-view-type 'long))
+    (vc-call region-history file buf lfrom lto)
+    (with-current-buffer buf
+      (vc-call-backend backend 'region-history-mode)
+      (set (make-local-variable 'log-view-vc-backend) backend)
+      (set (make-local-variable 'log-view-vc-fileset) file)
+      (set (make-local-variable 'revert-buffer-function)
+           (lambda (_ignore-auto _noconfirm)
+             (with-current-buffer buf
+               (let ((inhibit-read-only t)) (erase-buffer)))
+             (vc-call region-history file buf lfrom lto))))
+    (display-buffer buf)))
+
+;;;###autoload
 (defun vc-revert ()
   "Revert working copies of the selected fileset to their repository contents.
 This asks for confirmation if the buffer contents are not identical