merlin-language-server

Simple LSP protocol wrapper for `merlin`, written in reason

⚠️ Alpha quality

Overview

merlin-language-server is a thin wrapper over the excellent merlin tooling - implementing the LSP protocol on-top of merlin's protocol.

As with ocaml-language-server, this is not intended as a replacement for any existing Reason / OCaml tooling, but to make it more accessible across editors.

Why?

There are already two excellent language server implementations - reason-language-server and ocaml-language-server - why another one?

The current language-server landspace could be summarized with this table:

Language Server	Uses `merlin`	Implemented in `reason`	Supports Windows
`ocaml-language-server`	✅	❌	❌ (1)
`reason-language-server`	❌	✅	❌ (2)
`merlin-language-server`	✅	✅	✅

NOTE (1): I believe ocaml-language-server may support Windows, but I was not able to get it working.

NOTE (2): reason-language-server mentions Windows support as a goal, but again, it did not work for me. I contributed several fixes towards this (PRs #36, #130, #199), but there is still significant investment required to get support on parity with merlin on Windows.

The primary issue for me being that there was not a language server implementation that worked well for me on Windows. It turns out that merlin works great on Windows - so having a native-reason LSP implementation that uses merlin is a natural choice.

In the future, perhaps we could integrate this more fully into merlin at some point, or incorporate merlin as a library that we call directly.

Building

Prerequisites

You will need esy to build - npm install -g esy
For running tests, you will need node.

Build

git clone https://github.com/bryphe/merlin-language-server
esy install
esy build

Tests

Unit tests: esy x TestRunner.exe
E2E tests:
- cd test-e2e
- npm install
- npm test

Roadmap

Distribution
- First-class Oni integration
- VSCode Plugin
- NPM package with pre-built binaries
Features
- Text synchronization
  - textDocument/didOpen
  - textDocument/didChange
  - Full document sync
  - Incremental document sync
- Language Features
  - completion
  - hover
  - definition
  - implementation
  - references
  - signatureHelp
  - codeAction?
  - codeLens
  - formatting
  - rangeFormatting
  - onTypeFormatting

Contributions

Contributions & PRs are welcome! Please ensure that test coverage is added for any new functionality - either in the form of unit tests or E2E tests.

License

MIT License

bryphe/merlin-language-server