Shrink git conflicts

shrink-conflicts is a program which tries to minimise diff3-style git conflicts.

Workflow

As I work on resolving a conflict, I slowly make all three parts (left, right, and centre) more and more similar. As I do this, I repeatedly pass the conflict through shrink-conflicts to have it automatically simplified (and possibly elliminated). It's pretty nice.

shrink-conflicts reads data on stdin and prints it to stdout (ie. it's a "filter"). This means you can easily use it from within your text editor: just pipe the buffer through it.

Credit

I got the idea from git-mediate. shrink-conflicts is a re-implementation of (part of) git-mediate's functionality.

Example

Here's lib.rs:

impl Conflict {
<<<<<<<
    /// Is this conflict resolved?
    fn is_resolved(&self) -> bool {
        // TODO: Should we be handling the common part too?
        self.left.is_empty() && self.right.is_empty()
    }
|||||||
    fn is_resolved(&self) -> bool {
        self.left.is_empty() && self.right.is_empty()
    }
=======
    fn is_resolved(&self) -> bool {
        self.left.is_empty() && self.common.is_empty() && self.right.is_empty()
    }
>>>>>>>
}

Running this file through shrink-conflicts will have no effect yet. Let's copy the doc comment from the left part into the common and right parts.

impl Conflict {
<<<<<<<
    /// Is this conflict resolved?
    fn is_resolved(&self) -> bool {
        // TODO: Should we be handling the common part too?
        self.left.is_empty() && self.right.is_empty()
    }
|||||||
    /// Is this conflict resolved?
    fn is_resolved(&self) -> bool {
        self.left.is_empty() && self.right.is_empty()
    }
=======
    /// Is this conflict resolved?
    fn is_resolved(&self) -> bool {
        self.left.is_empty() && self.common.is_empty() && self.right.is_empty()
    }
>>>>>>>
}

Now when we run this through shrink-conflicts it detects that all three have a common prefix, and pulls it out:

$ shrink-conflicts <lib.rs
impl Conflict {
    /// Is this conflict resolved?
    fn is_resolved(&self) -> bool {
<<<<<<<
        // TODO: Should we be handling the common part too?
        self.left.is_empty() && self.right.is_empty()
|||||||
        self.left.is_empty() && self.right.is_empty()
=======
        self.left.is_empty() && self.common.is_empty() && self.right.is_empty()
>>>>>>>
    }
}

Now, let's delete the TODO.

impl Conflict {
    /// Is this conflict resolved?
    fn is_resolved(&self) -> bool {
<<<<<<<
        self.left.is_empty() && self.right.is_empty()
|||||||
        self.left.is_empty() && self.right.is_empty()
=======
        self.left.is_empty() && self.common.is_empty() && self.right.is_empty()
>>>>>>>
    }
}

This time, when we run the file through shrink-conflicts, it detects that the left and common parts are identical, and so selects the right part.

$ shrink-conflicts <lib.rs
impl Conflict {
    /// Is this conflict resolved?
    fn is_resolved(&self) -> bool {
        self.left.is_empty() && self.common.is_empty() && self.right.is_empty()
    }
}