This project contains an implementation of an LSP server for OCaml and a standalone implementation of the LSP protocol.

We recommend to install the server via a project such as opam or esy.

To install the lsp server in a particular opam switch:

$ opam pin add ocaml-lsp-server https://github.com/ocaml/ocaml-lsp.git
$ opam install ocaml-lsp-server

Note that you will need to run install the lsp server in every switch where you'd like to use it.

To add the lsp server to an esy project, add the following lines to your project's package.json:

  "devDependencies": {
    "@opam/ocaml-lsp-server": "*"
  },
  "resolutions": {
    "@opam/ocaml-lsp-server": "github:ocaml/ocaml-lsp:ocaml-lsp-server.opam#<git-commit-sha>"
  }

Note that you need to specify a specific git commit sha from this repository instead of <git-commit-sha> placeholder above.

This project uses submodules to handle dependencies. This is done so that users who install ocaml-lsp-server into their sandbox will not share constraints on the same dependencies that ocaml-lsp-server is using.

$ git clone --recurse-submodules http://github.com/ocaml/ocaml-lsp.git
$ cd ocaml-lsp
$ make build

The server supports the following queries:

• textDocument/completion
• completionItem/resolve
• textdocument/hover
• textDocument/signatureHelp
• textDocument/declaration
• textDocument/definition
• textDocument/typeDefinition
• textDocument/implementation
• textDocument/codeLens
• textDocument/documentHighlight
• textDocument/documentSymbol
• textDocument/references
• textDocument/documentColor
• textDocument/colorPresentation
• textDocument/formatting
• textDocument/rangeFormatting
• textDocument/onTypeFormatting
• textDocument/prepareRename
• textDocument/foldingRange
• textDocument/selectionRange
• workspace/symbol

Note that degrees of support for each LSP request are varying.

To run tests execute:

$ make test

Note that tests require Node.js and Yarn installed.

The lsp server uses merlin under the hood, but users are not required to have merlin installed. We vendor merlin because we currently heavily depend on some implementation details of merlin that make infeasible to upgrade the lsp server and merlin independently.

The implementation of the lsp protocol itself was taken from facebook's hack

Previously, this lsp server was a part of merlin, until it was realized that the lsp protocol covers a wider scope than merlin.

Note that the comparisons below make no claims of being objective and may be entirely out of date:

• reason-language-server This server supports bucklescript & reason. However, this project does not use merlin which means that it supports less versions of OCaml and offers less "smart" functionality - especially in the face of sources that do not yet compile.

• ocaml-language-server This project is extremely similar in the functionality it provides because it also reuses merlin on the backend. The essential difference is that this project is written in typescript, while our server is in OCaml. We feel that it's best to use OCaml to maximize the contributor pool.