saep / haskell-tools.nvim

Supercharge your Haskell experience in neovim!

haskell-tools.nvim

Supercharge your Haskell experience in neovim!

Quick Links

• Installation
• Quick Setup
• Features
• Advanced configuration
• Troubleshooting
• Recommendations

Prerequisites

Required

• neovim >= 0.8
• nvim-lspconfig
• plenary.nvim
• haskell-language-server

Optional

• telescope.nvim
• A local hoogle installation (recommended for better hoogle search performance)

Installation

Example using packer.nvim:

use {
  'MrcJkb/haskell-tools.nvim',
  requires = {
    'neovim/nvim-lspconfig',
    'nvim-lua/plenary.nvim',
    'nvim-telescope/telescope.nvim', -- optional
  },
  -- tag = 'x.y.z' -- [^1]
}

[^1] It is suggested to use the latest release tag and to update it manually, if you would like to avoid breaking changes.

Quick Setup

This plugin automatically configures the haskell-language-server neovim client.

⚠️ Do not call the lspconfig.hls setup or set up the lsp manually, as doing so may cause conflicts.

To get started quickly with the default setup, add the following to your neovim config:

local ht = require('haskell-tools')

local opts = { noremap = true, silent = true, buffer = bufnr }
ht.setup {
  hls = {
    -- See nvim-lspconfig's  suggested configuration for keymaps, etc.
    on_attach = function(client, bufnr)
      -- haskell-language-server relies heavily on codeLenses,
      -- so auto-refresh (see advanced configuration) is enabled by default
      vim.keymap.set('n', '<space>ca', vim.lsp.codelens.run, opts)
      vim.keymap.set('n', '<space>hs', ht.hoogle.hoogle_signature, opts)
      -- default_on_attach(client, bufnr)  -- if defined, see nvim-lspconfig
    end,
  },
}

If using a local hoogle installation, follow these instructions to generate a database.

Features

• Basic haskell-language-server functionality on par with nvim-lspconfig.hls

Beyond nvim-lspconfig.hls

• Clean shutdown of language server on exit to prevent corrupted files (see ghc #14533).
• Automatically adds capabilities for the following plugins, if loaded:
  • cmp-nvim-lsp (provides completion sources for nvim-cmp).
  • nvim-lsp-selection-range (Adds haskell-specific expand selection support).
• Automatically refreshes code lenses by default, which haskell-language-server heavily relies on. Can be disabled.
• The following code lenses are currently supported:

Show/Add type signatures for bindings without type signatures

Evaluate code snippets in comments

Make import lists fully explicit

Fix module names that do not match the file path

Beyond haskell-language-server

The below features are not implemented by haskell-language-server.

Hoogle-search for signature

• Search for the type signature under the cursor.
• Falls back to the word under the cursor if the type signature cannot be determined.
• Telescope keymaps:
  • <CR> to copy the selected entry ( :: ) to the clipboard.
  • <C-b> to open the selected entry's Hackage URL in a browser.
  • <C-r> to replace the word under the cursor with the selected entry.

require('haskell-tools').hoogle.hoogle_signature()

Use Hoogle search to fill holes

With the <C-r> keymap, the Hoogle search telescope integration can be used to fill holes.

Planned

For planned features, refer to the issues.

Advanced configuration

To modify the default configs, call

-- defaults
require('haskell-tools').setup {
  tools = { -- haskell-tools options
    codeLens = {
      -- Whether to automatically display/refresh codeLenses
      autoRefresh = true,
    },
    hoogle = {
      -- 'auto': Choose a mode automatically, based on what is available.
      -- 'telescope-local': Force use of a local installation.
      -- 'telescope-web': The online version (depends on curl).
      -- 'browser': Open hoogle search in the default browser.
      mode = 'auto', 
    },
  },
  hls = { -- LSP client options
    -- ...
    haskell = { -- haskell-language-server options
      formattingProvider = 'ormolu', 
      checkProject = true, -- Setting this to true could have a performance impact on large mono repos.
      -- ...
    }
  }
}

• The full list of defaults can be found here.
• To view all available language server settings (including those not set by this plugin), run haskell-language-server generate-default-config.
• For detailed descriptions of the configs, look at the haskell-language-server documentation.

How to disable individual code lenses

Some code lenses might be more interesting than others. For example, the importLens could be annoying if you prefer to import everything or use a custom prelude. Individual code lenses can be turned off by disabling them in the respective plugin configurations:

hls = {
  haskell = {
    plugin = {
      class = { -- missing class methods
        codeLensOn = false,
      },
      importLens = { -- make import lists fully explicit
        codeLensOn = false,
      },
      refineImports = { -- refine imports
        codeLensOn = false,
      },
      tactics = { -- wingman
        codeLensOn = false,
      },
      moduleName = { -- fix module names
        globalOn = false,
      },
      eval = { -- evaluate code snippets
        globalOn = false,
      },
      ['ghcide-type-lenses'] = { -- show/add missing type signatures
        globalOn = false,
      },
    },
  },
},

Troubleshooting

LSP features not working

Check which version of GHC you are using (:LspInfo). Sometimes, certain features take some time to be implemented for the latest GHC versions. You can see how well a specific GHC version is supported here.

Recommendations

Here are some other plugins I recommend for Haskell (and nix) development in neovim:

• MrcJkb/neotest-haskell: Interact with tests in neovim.
• luc-tielen/telescope_hoogle: Live Hoogle search.
• MrcJkb/telescope-manix: Nix search.
• mfussenegger/nvim-lint: As a fallback in case there are problems with haskell-language-server (e.g. in large mono repos).
• aloussase/scout: CLI for searching Hackage with telescope.nvim integration.