21 KiB
Configuration
Configuring haskell-language-server
Language servers like haskell-language-server
expose most of their configuration via the client (i.e. the editor).
That means that the way in which you configure the settings will depend on the client.
Most clients (editors) already have an opinion about how settings should be configured!
For example, in VS Code you use the graphical Settings tab or settings.json
, whereas in Emacs you use customization variables.
In the editor configuration section we give some pointers for popular editors, but you should consult the documentation for your specific editor if you have trouble.
However, we can say some high-level things about the kinds of configuration haskell-language-server
uses, and how to use them.
This can sound a bit confusing, but ultimately the client should present you with these options in a user-friendly way that makes sense for that editor.
Generic server options
The LSP protocol is designed to support many useful server configuration options generically. These are sent to the server by the client, and can be controlled without reference to a specific language.
For example, there are protocol methods for highlighting matching identifiers throughout a document. This is a capability that any server can implement, so the client can decide generically whether to ask the server to do it or not. So your editor can provide a setting to turn this on or off globally, for any language server you might use.
Settings like this are typically provided by the generic LSP client support for your editor, for example in Emacs by lsp-mode.
Generic editor options
Your editor may provide some settings that affect how the information from the language server is used. For example, whether popups are shown, or whether code lenses appear by default.
Settings like this are typically provided by the generic LSP client support for your editor, for example in Emacs by lsp-mode.
Language-specific server options
A specific language server can also have its own configuration options. These are still sent to the server by the client, but they can only be controlled by a specific client that knows about those options.
For example, haskell-language-server
allows you to choose the formatting provider which will be used for formatting Haskell source.
This option obviously would not make sense for language servers for other languages, or even for other Haskell language servers (which need not even support formatting).
Here is a list of the additional settings currently supported by haskell-language-server
, along with their setting key (you may not need to know this) and default:
- Formatting provider (
haskell.formattingProvider
, defaultormolu
): what formatter to use; one offloskell
,ormolu
,fourmolu
, orstylish-haskell
. - Max completions (
haskell.maxCompletions
, default 40): maximum number of completions sent to the LSP client. - Check project (
haskell.checkProject
, default true): whether to typecheck the entire project on initial load. As it is activated by default could drive to bad performance in large projects. - Check parents (
haskell.checkParents
, defaultCheckOnSave
): when to typecheck reverse dependencies of a file; one ofNeverCheck
,CheckOnSave
(means dependent/parent modules will only be checked when you save), orAlwaysCheck
(means re-typechecking them on every change).
Generic plugin configuration
Plugins have a generic config to control their behaviour. The schema of such config is:
haskell.plugin.${pluginName}.globalOn
: usually with default true. Whether the plugin is enabled at runtime or it is not. That is the option you might use if you want to disable completely a plugin.- Actual plugin names are:
ghcide-code-actions-fill-holes
,ghcide-completions
,ghcide-hover-and-symbols
,ghcide-type-lenses
,ghcide-code-actions-type-signatures
,ghcide-code-actions-bindings
,ghcide-code-actions-imports-exports
,eval
,moduleName
,pragmas
,importLens
,class
,hlint
,retrie
,rename
,splice
,stan
. - So to disable the import lens with an explicit list of module definitions you could set
haskell.plugin.importLens.globalOn: false
- Actual plugin names are:
haskell.plugin.${pluginName}.${lspCapability}On
: usually with default true. Whether a concrete plugin capability is enabled.- Capabilities are the different ways a lsp server can interact with the editor. The current available capabilities of the server are:
callHierarchy
,codeActions
,codeLens
,diagnostics
,hover
,symbols
,completion
,rename
. - Note that usually plugins don't provide all capabilities but some of them or even only one.
- So to disable code changes suggestions from the
hlint
plugin (but no diagnostics) you could sethaskell.plugin.hlint.codeActionsOn: false
- Capabilities are the different ways a lsp server can interact with the editor. The current available capabilities of the server are:
- Plugin specific configuration:
eval
:haskell.plugin.eval.config.diff
, default true: When reloading haddock test results in changes, mark it with WAS/NOW.haskell.plugin.eval.config.exception
, default false: When the command results in an exception, mark it with*** Exception:
.
rename
:haskell.plugin.rename.config.diff
, default false: Enables renaming across modules (experimental)
ghcide-completions
:haskell.plugin.ghcide-completions.config.snippetsOn
, default true: Inserts snippets when using code completions.haskell.plugin.ghcide-completions.config.autoExtendOn
, default true: Extends the import list automatically when completing a out-of-scope identifier.
ghcide-type-lenses
:haskell.plugin.ghcide-type-lenses.config.mode
, defaultalways
: Control how type lenses are shown. One ofalways
,exported
,diagnostics
.
hlint
:haskell.plugin.hlint.config.flags
, default empty: List of flags used by hlint.
ormolu
:haskell.plugin.ormolu.config.external
, defaultfalse
: Use an externalormolu
executable rather than the one packaged with HLS.
fourmolu
:haskell.plugin.fourmolu.config.external
, defaultfalse
: Use an externalfourmolu
executable rather than the one packaged with HLS. This reference of configuration can be outdated at any time but we can query thehaskell-server-executable
about what configuration is effectively used:
haskell-language-server generate-default-config
: will print the json configuration with all default values. It can be used as template to modify it.haskell-language-server vscode-extension-schema
: will print a json schema used to setup the haskell vscode extension. But it is useful to see what range of values can an option take and a description about it.
Settings like this are typically provided by the language-specific LSP client support for your editor, for example in Emacs by lsp-haskell
.
Client options
A particular client might also have some options of its own, for example to control how the server executable is started.
Settings like this are typically be provided by the language-specific LSP client support for your editor, for example in Emacs by lsp-haskell
.
Configuring your project build
haskell-language-server
has to compile your project in order to give you diagnostics, which means that it needs to know how to do so.
This is handled under the hood by the hie-bios application.
In turn, hie-bios
needs some configuration to identify all files, GHC options, etc., needed to compile a project.
There are several ways to provide this configuration to hie-bios
, detailed below.
Implicit configuration
If no hie.yaml
file is present, haskell-language-server
automatically detects your hie-bios
configuration using implicit-hie.
For most cases, this works just fine, and is the recommended way.
Explicit, generated configuration
Maybe using the implicit configuration does not suit you.
E.g., it does not work, or you prefer to have explicit configuration in your project.
In that case, you can automatically generate a hie.yaml
file, using implicit-hie:
gen-hie > hie.yaml # In the root directory of your project
Explicit, manual configuration
Maybe using the generated hie.yaml
file does not suit you.
E.g., it still does not work, or you want to fine-tune the configuration.
In that case, refer to the hie-bios explicit configuration documentation.
Keep in mind that you can start from the hie.yaml
file generated by implicit-hie
(see previous section) and modify it to your liking.
Examples of explicit hie.yaml
configurations
Basic Stack
cradle:
stack:
Basic Cabal
cradle:
cabal:
Single Stack component
cradle:
stack:
component: "haskell-language-server:lib"
Single Cabal component
cradle:
cabal:
component: "lib:haskell-language-server"
Multiple Stack components
cradle:
stack:
- path: "./test/functional/"
component: "haskell-language-server:func-test"
- path: "./exe/Main.hs"
component: "haskell-language-server:exe:haskell-language-server"
- path: "./exe/Wrapper.hs"
component: "haskell-language-server:exe:haskell-language-server-wrapper"
- path: "./src"
component: "haskell-language-server:lib"
- path: "./ghcide/src"
component: "ghcide:lib:ghcide"
- path: "./ghcide/exe"
component: "ghcide:exe:ghcide"
Multiple Cabal components
cradle:
cabal:
- path: "./test/functional/"
component: "haskell-language-server:func-test"
- path: "./test/utils/"
component: "haskell-language-server:hls-test-utils"
- path: "./exe/Main.hs"
component: "haskell-language-server:exe:haskell-language-server"
- path: "./exe/Wrapper.hs"
component: "haskell-language-server:exe:haskell-language-server-wrapper"
- path: "./src"
component: "lib:haskell-language-server"
- path: "./ghcide/src"
component: "ghcide:lib:ghcide"
- path: "./ghcide/exe"
component: "ghcide:exe:ghcide"
Custom program
You can explicitly state the program which should be used to collect the options by supplying the path to the program. It is interpreted relative to the current working directory if it is not an absolute path.
cradle:
bios:
program: ".hie-bios"
The complete configuration is a subset of
cradle:
cabal:
component: "optional component name"
stack:
component: "optional component name"
bios:
program: "program to run"
dependency-program: "optional program to run"
direct:
arguments: ["list","of","ghc","arguments"]
default:
none:
dependencies:
- someDep
How to show local documentation on hover
Haskell Language Server can display Haddock documentation on hover and completions if the project and
its dependencies have been built with the -haddock
GHC flag.
-
For cabal:
-
Add to your global config file (e.g.
~/.cabal/config
):program-default-options ghc-options: -haddock
-
Or, for a single project, run
cabal configure --ghc-options=-haddock
-
-
For stack, add to global
$STACK_ROOT\config.yaml
, or project'sstack.yaml
:ghc-options: '$everything': -haddock
Note that this flag will cause compilation errors if a dependency contains invalid Haddock markup, until GHC 9.0 which will report warnings instead.
Configuring your editor
Most editors provide a Haskell-specific extension that provides support for launching haskell-language-server
and talking to it, as well as exposing configuration options.
Editors typically assume that you have already installed haskell-language-server
(see above) and that the installation script put the haskell-language-server
and haskell-language-server-wrapper
binaries in your PATH
(usually ~/.local/bin
or ~/.cabal/bin
on Linux and macOS, %APPDATA%\local\bin
or %APPDATA%\cabal\bin
on Windows).
The exception is VS Code, which can automatically install the binaries if they are not installed already.
VS Code
Install from
the VSCode marketplace, or manually from the repository vscode-haskell.
The haskell-language-server
and haskell-language-server-wrapper
binaries will be automatically downloaded on an ad-hoc basis, but if you have them already installed on your PATH then it will just use them instead.
Configuration is done via the "Haskell" section of "Settings".
Sublime Text
Install LSP using Package Control.
Open Preferences > Package Settings > LSP > Settings
and add the following "haskell-language-server" client configuration to the "clients" key:
{
"clients": {
"haskell-language-server": {
"enabled": true,
"command": ["haskell-language-server-wrapper", "--lsp"],
"selector": "source.haskell"
}
}
}
See the Sublime Text LSP documentation for information on configuring the client. In particular, you can add a "settings" key to the "haskell-language-server" setting to configure specific HLS plugins as described elsewhere in these docs.
Neovim
Neovim provides a native LSP implementation with a Lua framework.
Plugins that streamline the setup of haskell-language-server
using Neovim's built-in LSP framework include:
- haskell-tools.nvim: A plugin with a focus on Haskell tooling, including
haskell-language-server
. - nvim-lspconfig: A collection of quickstart configs for various LSP servers.
- Includes a basic
hls
configuration.
- Includes a basic
Neovim is also compatible with the Vim plugins.
Vim
You can use Coc, LanguageClient-neovim or any other Vim Language server protocol client. Coc is recommend since it is the only complete LSP implementation for Vim and offers snippets and floating documentation out of the box.
Coc
Follow Coc's installation instructions.
Then issue :CocConfig
and add the following to your Coc config file.
Minimal Example
{
"languageserver": {
"haskell": {
"command": "haskell-language-server-wrapper",
"args": ["--lsp"],
"rootPatterns": ["*.cabal", "stack.yaml", "cabal.project", "package.yaml", "hie.yaml"],
"filetypes": ["haskell", "lhaskell"]
}
}
}
Example with Settings
{
"languageserver": {
"haskell": {
"command": "haskell-language-server-wrapper",
"args": ["--lsp"],
"rootPatterns": [ "*.cabal", "stack.yaml", "cabal.project", "package.yaml", "hie.yaml" ],
"filetypes": ["haskell", "lhaskell"],
"settings": {
"haskell": {
"checkParents": "CheckOnSave",
"checkProject": true,
"maxCompletions": 40,
"formattingProvider": "ormolu",
"plugin": {
"stan": { "globalOn": true }
}
}
}
}
}
}
LanguageClient-neovim
vim-plug
If you use vim-plug, then you can do this by e.g.,
including the following line in the Plug section of your init.vim
or ~/.vimrc
:
Plug 'autozimu/LanguageClient-neovim', {
\ 'branch': 'next',
\ 'do': 'bash install.sh'
\ }
and issuing a :PlugInstall
command within Neovim or Vim.
Clone the LanguageClient-neovim repo
As an alternative to using vim-plug shown above, clone LanguageClient-neovim
into ~/.vim/pack/XXX/start/
, where XXX
is just a name for your "plugin suite".
Configuration and sample ~/.vimrc
sections
set rtp+=~/.vim/pack/XXX/start/LanguageClient-neovim
let g:LanguageClient_serverCommands = { 'haskell': ['haskell-language-server-wrapper', '--lsp'] }
You'll probably want to add some mappings for common commands:
nnoremap <F5> :call LanguageClient_contextMenu()<CR>
map <Leader>lk :call LanguageClient#textDocument_hover()<CR>
map <Leader>lg :call LanguageClient#textDocument_definition()<CR>
map <Leader>lr :call LanguageClient#textDocument_rename()<CR>
map <Leader>lf :call LanguageClient#textDocument_formatting()<CR>
map <Leader>lb :call LanguageClient#textDocument_references()<CR>
map <Leader>la :call LanguageClient#textDocument_codeAction()<CR>
map <Leader>ls :call LanguageClient#textDocument_documentSymbol()<CR>
Use Ctrl+xCtrl+o (<C-x><C-o>
) to open up the auto-complete menu,
or for asynchronous auto-completion, follow the setup instructions on
LanguageClient.
If you'd like diagnostics to be highlighted, add a highlight group for ALEError
/ALEWarning
/ALEInfo
,
or customize g:LanguageClient_diagnosticsDisplay
:
hi link ALEError Error
hi Warning term=underline cterm=underline ctermfg=Yellow gui=undercurl guisp=Gold
hi link ALEWarning Warning
hi link ALEInfo SpellCap
If you're finding that the server isn't starting at the correct project root, it may also be helpful to also specify root markers:
let g:LanguageClient_rootMarkers = ['*.cabal', 'stack.yaml']
Further configuration can be done by pointing the g:LanguageClient_settingsPath
option
variable to the file in which you want to keep your LSP settings.
Atom
Install the two Atom packages atom-ide-ui and haskell,
$ apm install language-haskell atom-ide-ui haskell
Emacs
Emacs support can be provided by different combinations of packages:
- eglot (built-in from Emacs 29 onwards)
or
- lsp-mode, lsp-ui and lsp-haskell
You can install these manually if you are using plain Emacs; instructions for some specific flavours are included below.
Make sure to check the READMEs of each of these packages, which explain how to configure the
various parts of the Emacs integration.
In particular, lsp-haskell
provides customization options for the haskell-language-server
-specific parts,
such as the path to the server executable.
use-package eglot
If you are using vanilla emacs with use-package
, put the following into your ~/.emacs
.
This will install eglot
and enable it by default in haskell-mode
.
To configure haskell-language-server
we use the eglot-workspace-configuration
variable.
With M-x eglot-show-workspace-configuration
you can see the JSON that eglot
will send to haskell-language-server
.
See https://joaotavora.github.io/eglot/#Customizing-Eglot for more information.
As an example, the setting below will disable the stan
plugin.
(use-package eglot
:ensure t
:config
(add-hook 'haskell-mode-hook 'eglot-ensure)
:config
(setq-default eglot-workspace-configuration
'((haskell
(plugin
(stan
(globalOn . :json-false)))))) ;; disable stan
:custom
(eglot-autoshutdown t) ;; shutdown language server after closing last file
(eglot-confirm-server-initiated-edits nil) ;; allow edits without confirmation
)
doom-emacs
Manual installation of packages is not required.
Enable the lsp module and the haskell lang module with lsp flag in .doom.d/init.el
:
:tools
lsp
;; ...
:lang
(haskell +lsp)
then do $HOME/.emacs.d/bin/doom sync
Spacemacs
Manual installation of packages is not required.
Enable the haskell
layer and the lsp
layer in your Spacemacs config file:
dotspacemacs-configuration-layers
'(
haskell
lsp
;; ...
)
Kakoune
- Grab a copy of kak-lsp, and follow the setup instructions.
- Point your
kak-lsp.toml
tohaskell-language-server-wrapper
.
[language.haskell]
filetypes = ["haskell"]
roots = ["Setup.hs", "stack.yaml", "*.cabal"]
command = "haskell-language-server-wrapper"
args = ["--lsp"]
Helix
Once haskell-language-server-wrapper
is installed in your system, it will be used automatically by the editor.
For more details please refer to the helix guide on installing language servers