Diff for "MergingWithEmacs"

Using Emacs as a merger program

Emacs is bundled with an elisp program called Ediff which purpose is to help developers to visually apply patches. One of the various ediff commands is well suited to three way merging and can be used as a merger program with Mercurial.

Wrapping Emacs+Ediff call in a script

So to use Emacs as Mercurial merger program, dump the following content into a file in your PATH (don't forget to turn on the execute bit):

   #!/bin/sh
   
   set -e # bail out quickly on failure
   
   LOCAL="$1"
   BASE="$2"
   OTHER="$3"

   BACKUP="$LOCAL.orig"
   
   Restore ()
   {
       cp "$BACKUP" "$LOCAL" 
   }

   ExitOK ()
   {
       exit $?
   }

   # Back up our file
   cp "$LOCAL" "$BACKUP"

   # Attempt to do a non-interactive merge
   if which merge > /dev/null 2>&1 ; then
       if merge "$LOCAL" "$BASE" "$OTHER" 2> /dev/null; then
           # success!
           ExitOK 
       fi
       Restore
   elif which diff3 > /dev/null 2>&1 ; then
       if diff3 -m "$BACKUP" "$BASE" "$OTHER" > "$LOCAL" ; then
           # success
           ExitOK
       fi
       Restore
   fi

   if emacs -q --no-site-file --eval "(ediff-merge-with-ancestor \"$BACKUP\" \"$OTHER\" \"$BASE\" nil \"$LOCAL\")" 
   then       
       ExitOK
   fi

   echo "emacs-merge: failed to merge files"
   exit 1

   # End of file

Considering Mercurial is now able to premerge before running the merge tool and even does it by default (see hgrc(5)), I feel that attempts of merge with merge and diff3 are not needed anymore.

How the script works

This script tries first to automatically merge the files using the RCS merge program or the diff3 program. If the automatic merger fails merging the files because of a conflict or, neither merge nor diff3 are available on the system, then emacs is launched to let the developer resolve the conflicts.

Enabling the script usage

Don't forget to add an entry in your hgrc file (either ~/.hgrc or the local working copy .hg/hgrc) to point Mercurial at your merge command (let's call it emacs-merge)