unison/unison-src/transcripts/resolve.md

Resolving edit conflicts in ucm

.> builtins.merge

The ucm tool tracks edits to hashes in an object called a patch. When patches get merged, sometimes those patches will have conflicting edits. The replace.term command helps resolve such conflicts.

First, let's make a new namespace, example.resolve:

.> cd example.resolve

Now let's add a term named a.foo:

a.foo = 42

.example.resolve> add

We'll fork the namespace a into a new namespace b, so we can edit the two concurrently.

.example.resolve> fork a b

We'll also make a second fork c which we'll use as the target for our patch later.

.example.resolve> fork a c

Now let's make a change to foo in the a namespace:

.example.resolve> cd a

foo = 43

.example.resolve.a> update

And make a different change in the b namespace:

.example.resolve> cd .example.resolve.b

foo = 44

.example.resolve.b> update

The a and b namespaces now each contain a patch named patch. We can view these:

.example.resolve.b> cd .example.resolve
.example.resolve> view.patch a.patch
.example.resolve> view.patch b.patch

Let's now merge these namespaces into c:

.example.resolve> merge a c

.example.resolve> merge b c

The namespace c now has an edit conflict, since the term foo was edited in two different ways.

.example.resolve> cd c
.example.resolve.c> todo

We see that #44954ulpdf (the original hash of a.foo) got replaced with both the #8e68dvpr0a and #jdqoenu794.

We can resolve this conflict by picking one of the terms as the "winner":

.example.resolve.c> replace.term #44954ulpdf #8e68dvpr0a

This changes the merged c.patch so that only the edit from #44954ulpdf to #8e68dvpr0a remains:

.example.resolve.c> view.patch

We still have a remaining name conflict since it just so happened that both of the definitions in the edits were named foo.

.example.resolve.c> todo

We can resolve the name conflict by deleting one of the names.

.example.resolve.c> delete.term foo#jdqoenu794

And that's how you resolve edit conflicts with UCM.