How to get the full LSP support for Solidity in Neovim

Hardhat-VSCode extension provides official support for Vim and Neovim text editors via a standalone executable language server. It means that you will be able to achieve a complete LSP experience with syntax highlighting, autocompletion, go-to definitions, finding references, and marking warnings and errors in Neovim.

Does the hardhat LSP work with Foundry, Truffle, Brownie, etc.?

Yes, it does. Initially, I was skeptical about the hardhat LSP since Foundry is my main framework for working with Solidity. But it turns out that it works perfectly fine. From my experience, there is no need to tweak the config to support different frameworks.

How to install the Solidity LSP?

Hardhat for VSCode’s Solidity Language Server page most likely has all the information you may need to set this up in both Vim and Neovim.

The first part - LSP installation:

  1. You have to install the language server with (I am assuming that you have Node.js and npm installed):
    npm install @ignored/solidity-language-server -g
  2. Once you have the language server installed, you will have access to the standalone executable for the server: nomicfoundation-solidity-language-server --stdio. This will be passed to the Nvim config so that the lspconfig knows how to run the language server for Solidity.

Once you install the LSP, you can move to the Nvim config part.

How to set up the Solidity LSP in Neovim?

The following steps may vary depending on how you have your Nvim set up. I am using AstroNvim, which provides an excellent out-of-the-box experience and is a solid base for further configuration.

The Solidity Language Server page mentioned before provides a general guideline on configuring the init.lua file (or wherever you have your LSP config).

For Astronvim, I had to tweak it a little bit. The custom LSP definition page of the official Astronvim documentation has been helpful.

  1. Add the language server to the servers table. It has to be in a string format. You can name it however you like. I went with “solidity”.
  2. In ["server-settings"], you have to add appropriate config options (the same as defined on the Solidity LSP page). The cmd is the most important setting. Neovim will know how to start the LSP. By additionally configuring the filetypes and root_dir, the language server will start automatically whenever a Solidity file is opened. 
    -- Extend LSP configuration
lsp = {
    -- enable servers that you already have installed without mason
    servers = {
        -- "pyright",
        "solidity"
    },
-- Add overrides for LSP server settings. The keys are the name of the server.
    ["server-settings"] = {
        solidity = {
            cmd = { 'nomicfoundation-solidity-language-server', '--stdio' },
            filetypes = { 'solidity' },
            root_dir = require("lspconfig.util").find_git_ancestor,
            single_file_support = true,
        },
    },
},

With this done, you should be ready to go. Remember that you might have to restart your terminal session to apply changes.

Update: After using this for a while, I’ve stumbled upon a couple of issues in big monorepos. In Foundry projects (or in a mix of Hardhat with Foundry), sometimes the forge-std library is not found in some of the files. Changing the root_dir line in the config above solves the problem most of the time.

solidity = {
    cmd = { 'nomicfoundation-solidity-language-server', '--stdio' },
    filetypes = { 'solidity' },
-	root_dir = require("lspconfig.util").find_git_ancestor,
+	require("lspconfig.util").root_pattern "foundry.toml",
    single_file_support = true,
},

Update v2: Recently, I migrated away from Astronvim to my own tailor-made Nvim config. When it comes to the LSP support, I went with LSP Zero. The Solidity configuration is similar to the one described above. In your lsp.lua file or wherever you do the lsp configuration, add these lines:

-- given: `local lsp = require('lsp-zero').preset({"recommended"})`
-- the snippet below will add Solidity lsp to your config

lsp.use('solidity', {
    cmd = { 'nomicfoundation-solidity-language-server', '--stdio' },
    filetypes = { 'solidity' },
    root_dir = require("lspconfig.util").find_git_ancestor,
    single_file_support = true,
})

References