vdiff

A tool like vimdiff for Emacs

Table of Contents

• vdiff
  • Introduction
  • Recent (Significant) Changes
  • Screenshot
  • Installation and Usage
  • Hydra
  • Further customization

Introduction

vdiff compares two or three buffers on the basis of the output from the diff tool. The buffers are kept synchronized so that as you move through one of the buffers the top of the active buffer aligns with the corresponding top of the other buffer(s). This is similar to how ediff works, but in ediff you use a third “control buffer” to move through the diffed buffers. The key difference is that in vdiff you are meant to actively edit one of the buffers and the display will update automatically for the other buffer. Similar to ediff, vdiff provides commands to “send” and “receive” hunks from one buffer to the other as well as commands to traverse the diff hunks, which are useful if you are trying to merge changes. In contrast to ediff, vdiff also provides folding capabilities to fold sections of the buffers that don’t contain changes. This folding occurs automatically. Finally, you are encouraged to bind a key to `vdiff-hydra/body’, which will use hydra.el (in ELPA) to create a convenient transient keymap containing most of the useful vdiff commands.

This functionality is all inspired by (but not equivalent to) the vimdiff tool from vim.

Contributions and suggestions are very welcome.

Recent (Significant) Changes

• [2019-02-26] If the region is active when changes are sent to other buffers, only lines in the intersection of the region and any hunks are sent. This allows sending individual lines, similar to how individual lines can be staged in magit.
• [2018-04-17] Add option to use various git diff algorithms. See vdiff-diff-algorithm for options.
• [2017-05-17] Split vdiff-magit.el into separate repository.
• [2017-02-01] Added magit integration functions in vdiff-magit.el.
• [2016-07-25] Added three-way diff support. See vdiff-buffers3 and vdiff-files3.

Screenshot

Basic two file diff with refined hunks

Three file diff with targets for sending changes

Installation and Usage

vdiff is available in MELPA, which is the recommended way to install it and keep it up to date. To install it you may do M-x package-install RET vdiff RET.

To start a vdiff session, the main entry points are

Command	Description
vdiff-buffers	Diff two open buffers
vdiff-files	Diff two files
vdiff-buffers3	Diff three open buffers
vdiff-files3	Diff three files
vdiff-current-file	Like ediff-current-file (Diff buffer with disk version of file)
vdiff-merge-conflict	Use vdiff to resolve merge conflicts in current file

After installing you can bind the commands to your preferred key prefix like this

(require 'vdiff)
(define-key vdiff-mode-map (kbd "C-c") vdiff-mode-prefix-map)

which will bind most of the commands under the C-c prefix when vdiff-mode is active. Of course you can pick whatever prefix you prefer. With the C-c prefix the commands would be

Basics

Key	Command	Description
C-c g	vdiff-switch-buffer	Switch buffers at matching line
C-c n	vdiff-next-hunk	Move to next hunk in buffer
C-c p	vdiff-previous-hunk	Move to previous hunk in buffer
C-c h	vdiff-hydra/body	Enter vdiff-hydra

Viewing and Transmitting Changes Between Buffers

Key	Command	Description
C-c r	vdiff-receive-changes	Receive change from other buffer
C-c R	vdiff-receive-changes-and-step	Same as C-c r then C-c n
C-c s	vdiff-send-changes	Send this change(s) to other buffer
C-c S	vdiff-send-changes-and-step	Same as C-c s then C-c n
C-c f	vdiff-refine-this-hunk	Highlight changed words in hunk
C-c x	vdiff-remove-refinements-in-hunk	Remove refinement highlighting
(none)	vdiff-refine-this-hunk-symbol	Refine based on symbols
(none)	vdiff-refine-this-hunk-word	Refine based on words
C-c F	vdiff-refine-all-hunks	Highlight changed words
(none)	vdiff-refine-all-hunks-symbol	Refine all based on symbols
(none)	vdiff-refine-all-hunks-word	Refine all based on words

Folds

Key	Command	Description
C-c N	vdiff-next-fold	Move to next fold in buffer
C-c P	vdiff-previous-fold	Move to previous fold in buffer
C-c c	vdiff-close-fold	Close fold at point or in region
C-c C	vdiff-close-all-folds	Close all folds in buffer
C-c t	vdiff-close-other-folds	Close all other folds in buffer
C-c o	vdiff-open-fold	Open fold at point or in region
C-c O	vdiff-open-all-folds	Open all folds in buffer

Ignoring case and whitespace

Key	Command	Description
C-c i c	vdiff-toggle-case	Toggle ignoring of case
C-c i w	vdiff-toggle-whitespace	Toggle ignoring of case

Saving, Updating and Exiting

Key	Command	Description
C-c w	vdiff-save-buffers	Save both buffers
C-c u	vdiff-refresh	Force diff refresh
(none)	vdiff-restore-windows	Restore window configuration
C-c q	vdiff-quit	Quit vdiff

Evil-mode users might prefer something like the following to use a comma as a prefix in normal state.

(require 'vdiff)
(require 'evil)
(evil-define-key 'normal vdiff-mode-map "," vdiff-mode-prefix-map)

vimdiff-like binding are provided by evil-collection’s evil-collection-vdiff.el

Hydra

Using the hydra package, vdiff-hydra allows quick movement and changes to be made in the buffer. By default it lives on the h command in the prefix map. Bind vdiff-hydra/body directly to customize this key binding.

Further customization

The current customization options and their defaults are

;; Whether to lock scrolling by default when starting vdiff
(setq vdiff-lock-scrolling t)

;; diff program/algorithm to use. Allows choice of diff or git diff along with
;; the various algorithms provided by these commands. See
;; `vdiff-diff-algorithms' for the associated command line arguments.
(setq vdiff-diff-algorithm 'diff)

;; diff3 command to use. Specify as a list where the car is the command to use
;; and the remaining elements are the arguments to the command.
(setq vdiff-diff3-command '("diff3"))

;; Don't use folding in vdiff buffers if non-nil.
(setq vdiff-disable-folding nil)

;; Unchanged lines to leave unfolded around a fold
(setq vdiff-fold-padding 6)

;; Minimum number of lines to fold
(setq vdiff-min-fold-size 4)

;; If non-nil, allow closing new folds around point after updates.
(setq vdiff-may-close-fold-on-point t)

;; Function that returns the string printed for a closed fold. The arguments
;; passed are the number of lines folded, the text on the first line, and the
;; width of the buffer.
(setq vdiff-fold-string-function 'vdiff-fold-string-default)

;; Default syntax table class code to use for identifying "words" in
;; `vdiff-refine-this-change'. Some useful options are
;; 
;; "w"   (default) words
;; "w_"  symbols (words plus symbol constituents)
;; 
;; For more information see
;; https://www.gnu.org/software/emacs/manual/html_node/elisp/Syntax-Class-Table.html
(setq vdiff-default-refinement-syntax-code "w")

;; If non-nil, automatically refine all hunks.
(setq vdiff-auto-refine nil)

;; How to represent subtractions (i.e., deleted lines). The
;; default is full which means add the same number of (fake) lines
;; as those that were removed. The choice single means add only one
;; fake line. The choice fringe means don't add lines but do
;; indicate the subtraction location in the fringe.
(setq vdiff-subtraction-style 'full)

;; Character to use for filling subtraction lines. See also
;; `vdiff-subtraction-style'.
(setq vdiff-subtraction-fill-char ?-)