Language Server Protocol (LSP)

[mmsaki]

Motivation

This PR introduces native Language Server Protocol (LSP) support to Foundry via a new forge lsp command.

The motivation behind this is to provide a first-class developer experience for Solidity projects using Foundry by exposing core compiler features (like linting, syntax errors, remappings, etc.) directly to LSP-compatible editors such as Neovim and VSCode.

Previously, users had to rely on external plugins or custom tooling to get real-time feedback while editing Solidity code. This native integration unlocks accurate diagnostics, contextual tooling, and seamless integration with Forge projects out of the box.

Solution

This PR adds:

• A new command: forge lsp
• A tokio-based LSP server implementation using tower-lsp
• The server is implemented in crates/lsp, and registered as a new Forge subcommand.
• Designed for extensibility: future support for hover, go-to-definition, and code actions is planned.
• Initial support for forge lint notification via "textDocument/publishDiagnostics" requests with streaming updates

PR Checklist

• Added Tests
• Added Documentation
• forge lint errors
• Diagnostics (compilation errors and warnings)

Planned

• Go-to-definition
• Symbol search and references
• Code completion
• Hover information
• Code formatting
• Code Actions
• Rename

[0xClandestine]

Thanks for carrying the torch on this, I have wanted a solid LSP for what feels like ages. The fact that forge lint is built-in is the cherry on top, well done brother.

[mmsaki]

Thanks for carrying the torch on this, I have wanted a solid LSP for what feels like ages. The fact that forge lint built-in is the cherry on top, well done brother.

It's so underrated. Already used the LSP to remove 84 unused imports in uniswap v4-core 👀 see PR Uniswap/v4-core#979, refactoring 45 files really easy with the LSP even without all the other features.

@0xClandestine Thanks for your work on forge lint too.

[0xClandestine]

@mmsaki Lol, I had a similar PR the other day forge lint is putting in work.

This actually solves one of my main frustrations when running forge lint on larger repos, the output is super noisy without filtering. With forge lsp you can simply navigate to your desired file and hover over concerning highlights.

Anyways, I was able to get it to work with vscode (and cursor) using the following extension and config if others are interested in trying it out:

[
  {
    "languageId": "solidity",
    "command": "forge",
    "fileExtensions": [
      ".sol"
    ],
    "args": [
      "lsp"
    ]
  }
]

[mmsaki]

@0xClandestine Thanks for testing it on vscode! Looks amazing 🙌.

[DaniPopes]

this does nothing? I think stdin/stdout should be the default

[mmsaki]

it doesn’t do anything at the moment 🤔 spec recommended to use the —stdio flag just to be explicit which transport method we use but maybe we don’t need to do it after all. I think we can remove it.

[DaniPopes]

Ah I see, this is fine then

[DaniPopes]

we can use SHORT_VERSION from foundry_common

[sambacha]

checkout https://github.com/ferranbt/solstice/tree/main/extension for potential reference

[mmsaki]

@DaniPopes can you help with the ci failures, is there something I am doing wrong with the way I set up my tests that they keep failing in CI but locally pass. The lsp implementation depends on forge being installed and available in PATH and test stored in crates/lsp/testdata/*. Could my test failing CI because of that or a different reason?