Overview

Knit Merge is kind of merging that gives similar results to weave merge. It was introduced in bzr 0.8.

Like weave merge, it

• Uses historical information about the individual lines to determine which should appear.
• Handles criss-cross merging
• Handles cherrypicking (not currently implemented).

Unlike weave merge, it

• Uses annotation information rather than line identity
• Only requres historical information about differing lines.
• Can be applied to both Weave and Knit data files

Algorithm

Simple case

As described by Martin Pool:

• Do a two-way diff between the two versions to be merged. Within the difference regions, we need to determine whether each line is unborn, live, or killed in the other side. Taking the lines from the left-hand-side conflict region first, get the line origins. If that origin is in the merged-revisions set of the right hand side, then the line has been deleted (or moved) on the right hand side. Otherwise, it's new on the left hand side.

Extension to cherry-picks

One way to expand support for cherry-picks is as follows:

Given a cherrypick BASE, generate a second merge plan. Compare the merge plan to the first merge plan. Where the new-OTHER lines agree, they should be turned to killed-THIS. Where killed-THIS lines agree, they should be turned into new-OTHER.

Future extension

Martin Pool again:

• This can still be improved for some criss-cross merge cases by recording when the user explicitly choses a resolution to a conflict, but I think this may give comparable results to current weave merge.

I would like to see a concept of line identity added to knits, so that the initial matching can be highly accurate. We can add convergence support on top of that. --AaronBentley

Example

Result of comparison, with annotations added

  My dog has
  <<<<<<< OTHER
b fleas
d and a bad attitude
e and sneakers
  =======
c interesting habits
f a skateboard
  >>>>>>> THIS

Ancestors of THIS: c, f, b Ancestors of OTHER: c, f, b, d, e

Plan-merge result

common       My dog has
             <<<<<<< OTHER
killed-THIS  fleas
new-OTHER    and a bad attitude
new-OTHER    and sneakers
             =======
killed-OTHER interesting habits
killed-OTHER a skateboard
             >>>>>>> THIS

After removing killed lines:

My dog has
and a bad attitude
and sneakers