Merge Conflict Assistant

This is a language server implementation to assist with resolving merge conflicts in files. The conflicts in a file will be returned as Diagnostics and show as errors like any other syntax error. Code Actions for these are made available which will show the branch, tag, or whatever name is included in the conflict markers.

Features

The names shown are based on the conflict markers. If branch names or hashes are included like git does that is what you will see in the list. You choose which portion you want to keep. There is also a "drop all" option which removes the marker and all of the impacted code completely. No worries, it is an editor undo away if you decided you chose poorly.

The conflicts are marked as errors which means your editor should let you easily jump between the conflicts.

Conflict Marker Formats

Diff3

The server detects the standard two-way conflict marker format and its diff3 variant with an ancestor (|||||||) section:

<<<<<<< HEAD
your changes
||||||| original
ancestor content
=======
incoming changes
>>>>>>> branch-name

Code actions: Keep HEAD, Keep branch-name, Keep ancestor (diff3 only), Keep both, and Drop all.

jj snapshot format

The server also detects jj snapshot conflicts, produced by Jujutsu VCS when configured with ui.conflict-marker-style = "snapshot". A snapshot conflict materializes each side of a conflict as a complete content snapshot rather than as a diff:

<<<<<<< conflict 1 of 1
+++++++ rtsqusxu 2768b0b9 "commit A"
apple
grapefruit
orange
------- vpxusssl 38d49363 "merge base"
apple
grape
orange
+++++++ ysrnknol 7a20f389 "commit B"
APPLE
GRAPE
ORANGE
>>>>>>> conflict 1 of 1 ends

Detection routes on the first marker inside the block: a <<<<<<< followed by +++++++ is a snapshot conflict; a <<<<<<< followed by ======= or ||||||| is a diff3-style conflict.

Code actions for each snapshot region:

• Keep '<label>' for each +++++++ side (verbatim label from the marker line).
• Keep '<label>' for each ------- base (one action per base; a conflict with N sides has N−1 bases).
• Keep all sides — concatenates all side content in document order; base is omitted.
• Drop all — removes the entire conflict block.

Limitation: marker tokens must be exactly 7 characters (<<<<<<<, +++++++, -------, >>>>>>>). Runs of 8 or more identical characters are treated as file content, not markers. jj can emit longer markers when 7-character sequences appear in file content; if your codebase triggers this, open an issue.

Mixed-format files

A file containing both a diff3-style conflict block and a jj snapshot conflict block produces a single error diagnostic at the opening line of the second (conflicting-style) block. No code actions are offered for any conflict in the file.

Install

Build. Copy it somewhere in your path. Then add the tool to you editor as a language server.

Helix

Add the following to languages.toml

[language-server.merge-conflict-assistant]
command = "merge-conflict-assistant"

Now you can put the "merge-conflict-assistant" into the list of language servers for whatever languages you want to use it in. !NOTE! Always add it after the main LSPs for the language. This ensures the main LSP catches and flags warnings and errors.

As an example for Rust you want

language-servers = ["rust-analyzer", "merge-conflict-assistant"]

NixOS / Home Manager

A Home Manager module is provided via the flake output homeManagerModules.helix.

Flake Input

Add the following to your flake inputs:

merge-conflict-assistant = {
  url = "github:shaleh/merge-conflict-assistant";
  inputs.nixpkgs.follows = "nixpkgs";
};

Module Setup

Add the module to your Home Manager sharedModules:

home-manager.sharedModules = [
  inputs.merge-conflict-assistant.homeManagerModules.helix
];

The module automatically sets the command for the language server when programs.helix.enable = true, so no manual languages.toml configuration is needed for the server definition.

Language Configuration

You still need to add merge-conflict-assistant to the language servers for whichever languages you want to use it with.

In your Home Manager config:

programs.helix.languages = {
  language = [
    {
      name = "rust";
      language-servers = [ "rust-analyzer" "merge-conflict-assistant" ];
    }
  ];
};

As noted above, always add merge-conflict-assistant after the primary LSP for the language.