haskell-language-server
Integration point for ghcide and haskell-ide-engine. One IDE to rule
them all. Read the project's
background.
Features
-
Code evaluation codelens (Tutorial):
-
Type information and documentation on hover. Note that currently, in order for docs to be displayed for dependencies, they must have been built with GHC's -haddock
flag:
-
For cabal:
-
For stack, add to global $STACK_ROOT\config.yaml
, or project's stack.yaml
:
ghc-options:
"$everything": -haddock
This will cause compilation errors if a dependency contains invalid Haddock markup, though from GHC version 9.0, these will be demoted to warnings.
-
Integration with retrie
-
Code lenses for explicit import lists
-
Many more (TBD)
Installation
Prerequisites
- For standalone
.hs
/.lhs
files, ghc must be installed and on the PATH. The easiest way to install it is with ghcup or Chocolatey on Windows.
- For Cabal based projects, both ghc and cabal-install must be installed and on the PATH. It can also be installed with ghcup or Chocolatey on Windows.
- For Stack based projects, stack must be installed and on the PATH.
ghcup
If you are using ghcup
to manage your installations, you can install the latest version of haskell-language-server
with
ghcup install hls
Visual Studio Code
If you are using Visual Studio Code, the Haskell extension will automatically download and install haskell-language-server
for you.
Pre-built binaries
There are pre-built binaries available from the releases page for Linux, Windows and macOS.
To install, download the haskell-language-server-wrapper
executable for your platform as well as any haskell-language-server
executables for the GHC versions you plan on working with, and either put them on your PATH or point your client to them.
Installation from source
Common pre-requirements
stack
or cabal
must be in your PATH
- You need stack version >= 2.1.1 or cabal >= 2.4.0.0
git
must be in your PATH
- The directory where
stack
or cabal
put the binaries must be in you PATH:
- For stack you can get it with
stack path --local-bin
- For cabal it is by default
$HOME/.cabal/bin
in linux and %APPDATA%\cabal\bin
in windows.
Tip: you can quickly check if some command is in your path by running the command.
If you receive some meaningful output instead of "command not found"-like message
then it means you have the command in PATH.
Linux-specific pre-requirements
On Linux you will need install a couple of extra libraries:
Debian 9/Ubuntu 18.04 or earlier:
sudo apt install libicu-dev libtinfo-dev libgmp-dev zlib1g-dev
Debian 10/Ubuntu 18.10 or later:
sudo apt install libicu-dev libncurses-dev libgmp-dev zlib1g-dev
Fedora:
sudo dnf install libicu-devel ncurses-devel zlib-devel
Windows-specific pre-requirements
In order to avoid problems with long paths on Windows you can do either one of the following:
-
Clone the haskell-language-server
to a short path, for example the root of your logical drive (e.g. to
C:\hls
). Even if you choose C:\haskell-language-server
you could hit the problem. If this doesn't work or you want to use a longer path, try the second option.
-
If the Local Group Policy Editor
is available on your system, go to: Local Computer Policy -> Computer Configuration -> Administrative Templates -> System -> Filesystem
set Enable Win32 long paths
to Enabled
. If you don't have the policy editor you can use regedit by using the following instructions here. You also need to configure git to allow longer paths by using unicode paths. To set this for all your git repositories use git config --system core.longpaths true
(you probably need an administrative shell for this) or for just this one repository use git config core.longpaths true
.
In addition make sure haskell-language-server.exe
is not running by closing your editor, otherwise in case of an upgrade the executable can not be installed.
Download the source code
git clone https://github.com/haskell/haskell-language-server --recurse-submodules
cd haskell-language-server
Building
Note, on first invocation of the build script with stack, a GHC is being installed for execution.
The GHC used for the install.hs
can be adjusted in ./install/stack.yaml
by using a different resolver.
Available commands can be seen with:
stack ./install.hs help
Remember, this will take time to download a Stackage-LTS and an appropriate GHC for build
haskell-language-server the first time.
Install via cabal
The install-script can be invoked via cabal
instead of stack
with the command
cabal v2-run ./install.hs --project-file install/shake.project <target>
or using the existing alias script
./cabal-hls-install <target>
Running the script with cabal on windows requires a cabal version greater or equal to 3.0.0.0
.
For brevity, only the stack
-based commands are presented in the following sections.
Install specific GHC Version
The script will install the executables haskell-language-server-wrapper
and haskell-language-server
.
It will copy the latter appending the used ghc version, needed by the wrapper to choose the suitable version
for the project at hand.
So installing the executables directly with stack install
or cabal v2-install
may not be enough
for it to work properly.
Install haskell-language-server for the latest available and supported GHC version (and hoogle docs):
stack ./install.hs hls
Install haskell-language-server for a specific GHC version (and hoogle docs):
stack ./install.hs hls-8.8.3
hls-8.8.3
target will build the project and install haskell-language-server-wrapper
,
haskell-language-server
, haskell-language-server-8.8.3
and haskell-language-server-8.8
executables.
The Haskell Language Server can also be built with cabal v2-build
instead of stack build
.
This has the advantage that you can decide how the GHC versions have been installed.
To see what GHC versions are available, the command cabal-hls-install ghcs
can be used.
It will list all supported GHC versions that are on the path for build with their respective installation directory.
If you think, this list is incomplete, you can try to modify the PATH variable, such that the executables can be found.
Note, that the targets hls
and data
depend on the found GHC versions.
An example output is:
> ./cabal-hls-install ghcs
******************************************************************
Found the following GHC paths:
ghc-8.6.5: /opt/bin/ghc-8.6.5
ghc-8.8.3: /opt/bin/ghc-8.8.3
******************************************************************
If your desired ghc has been found, you use it to install haskell-language-server.
./cabal-hls-install hls-8.6.5
Installation from Hackage
Direct installation from Hackage, while possible via cabal install haskell-language-server
, is not recommended for most people.
Said command builds the haskell-language-server
binary and installs it in the default Cabal binaries folder,
but the binary will only work with projects that use the same GHC version that built it.
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 which 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
, default ormolu
): what formatter to use; one of floskell
, ormolu
, fourmolu
, stylish-haskell
, or brittany
(if compiled with AGPL)
- Format on imports (
haskell.formatOnImportOn
, default true): whether to format after adding an import
- Maximum number of problems to report (
haskell.maxNumberOfProblems
, default 100): the maximum number of problems the server will send to the client
- Diagnostics on change (
haskell.diagnosticsOnChange
, default true): (currently unused)
- Completion snippets (
haskell.completionSnippetsOn
, default true): whether to support completion snippets
- Liquid Haskell (
haskell.liquidOn
, default false): whether to enable Liquid Haskell support (currently unused until the Liquid Haskell support is functional again)
- Hlint (
haskell.hlintOn
, default true): whether to enable Hlint support
- Max completions (
haskell.maxCompletions
, default 40): maximum number of completions sent to the LSP client.
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 by the hie-bios
project.
For a full explanation of how hie-bios
determines the project build configuration, and how to configure it manually, refer to the hie-bios
README.
At the moment, haskell-language-server
has some limited support to automatically detect your project build configuration.
The plan is to improve it to handle most use cases.
However, for now, the most reliable way is to manually configure hie-bios
using a hie.yaml
file in the root of the workspace.
A hie.yaml
file explicitly describes how to setup the environment to compile the various parts of your project.
For that you need to know what components your project has, and the path associated with each one.
So you will need some knowledge about
stack or cabal components.
You also can use this utility to automatically generate hie.yaml
files for
the most common stack and cabal configurations
For example, to state that you want to use stack
then the configuration file
would look like:
cradle:
stack:
component: "haskell-language-server:lib"
If you use cabal
then you probably need to specify which component you want
to use.
cradle:
cabal:
component: "lib:haskell-language-server"
If you have a project with multiple components, you can use a cabal-multi
cradle:
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"
Equivalently, you can use stack:
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"
Or 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
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.
Using Haskell Language Server with 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".
Using Haskell Language Server with Sublime Text
- Install LSP using Package Control
- From Sublime Text, go to Preferences and search for LSP Settings
- Paste in these settings. Make sure to change the command path to your
haskell-language-server-wrapper
{
"clients": {
"haskell-language-server": {
"command": ["haskell-language-server-wrapper", "--lsp"],
"scopes": ["source.haskell"],
"syntaxes": ["Packages/Haskell/Haskell.sublime-syntax"],
"languageId": "haskell"
}
}
}
Now open a Haskell project with Sublime Text and enable Language Server in the project.
You should have these features available:
- Errors are underlined in red
- LSP: Show Diagnostics will show a list of hints and errors
- LSP: Format Document will prettify the file
Using Haskell Language Server with Vim or Neovim
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 Neovim 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.
{
"languageserver": {
"haskell": {
"command": "haskell-language-server-wrapper",
"args": ["--lsp"],
"rootPatterns": ["*.cabal", "stack.yaml", "cabal.project", "package.yaml", "hie.yaml"],
"filetypes": ["haskell", "lhaskell"]
}
}
}
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
variable to the file in which you want to keep your LSP settings.
Using Haskell Language Server with Atom
Install the two Atom packages atom-ide-ui and haskell,
$ apm install language-haskell atom-ide-ui haskell
Using haskell-language-server with Emacs
Emacs support is provided by a combination of the following packages:
lsp-mode
lsp-ui
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.
Using haskell-language-server with 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
Using haskell-language-server with 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
;; ...
)
Using haskell-language-server with Kakoune
- Grab a copy of kak-lsp, and follow the setup instructions.
- Point your
kak-lsp.toml
to haskell-language-server-wrapper
.
[language.haskell]
filetypes = ["haskell"]
roots = ["Setup.hs", "stack.yaml", "*.cabal"]
command = "haskell-language-server-wrapper"
args = ["--lsp"]
Known limitations
Preprocessor
HLS is not yet able to find project preprocessors, which may result in could not execute: <preprocessor>
errors. This problem is
tracked in https://github.com/haskell/haskell-language-server/issues/176 and originally comes from https://github.com/mpickering/hie-bios/issues/125
As a workaround, you need to ensure the preprocessor is available in the path (install globally with Stack or Cabal, provide in shell.nix
, etc.).
Example with tasty-discover
:
{-# OPTIONS_GHC -F -pgmF tasty-discover #-}
This returns an error in HLS if 'tasty-discover' is not in the path: could not execute: tasty-discover
.
Troubleshooting
Common issues
Difficulties with Stack and Paths_
modules
These are known to be somewhat buggy at the moment: https://github.com/haskell/haskell-language-server/issues/478.
This issue should be fixed in Stack versions >= 2.5.
Problems with dynamic linking
As haskell-language-server prebuilt binaries are statically linked, they don't play well with projects using dynamic linking.
An usual symptom is the presence of errors containing unknown symbol
and it is typical in arch linux, where a dynamically linked version of ghc is used.
The workaround is to use a version of haskell-language-server compiled from source with -dynamic
enabled`. See more details here.
Troubleshooting the server
Diagnostic mode
The haskell-language-server
executable can be run in diagnostic mode, where it will just try to load modules from your project, printing all of its output to stdout.
This makes it much easier to see what's going on and to diagnose build-related problems.
To do this, simply run the executable directly from your shell in the project root.
You can either run it without an argument, in which case it will load random modules, or with a path, in which case it will load modules in that file or directory.
Examining the log
Most clients will launch haskell-language-server
with --logfile
to make it write a log file.
Please consult the documentation for your client to find out where this is (or how to set it).
The log will contain all the messages that are sent to the server and its responses.
This is helpful for low-level debugging: if you expect a certain action to happen, you can look in the log to see if the corresponding messages are
sent, or if there are any errors.
To get a more verbose, also pass --debug
to the executable.
Troubleshooting the client
Many clients provide diagnostic information about a LSP session.
In particular, look for a way to get the status of the server, the server stderr, or a log of the messages that the client has sent to the server.
For example, lsp-mode
provides all of these (see its troubleshooting page for details).
The most common client-related problem is the client simply not finding the server executable, so make sure that you have the right PATH
and you have configured
it to look for the right executable.
Contributing
❤️ The Haskell tooling dream is near, we need your help! ❤️
- Join our IRC channel at
#haskell-ide-engine
on freenode
.
- Fork this repo and ghcide and hack as much as you can.
Style guidelines
The project includes a .editorconfig
file with the editor basic settings used by the project.
However, most editors will need some action to honour those settings automatically.
For example vscode needs to have installed a specific extension.
Please, try to follow those basic settings to keep the codebase as uniform as possible.
Building haskell-language-server
The project can be built with both cabal build
and stack build
.
haskell-language-server can also be used with itself. We provide preset samples of hie.yaml
for Cabal and Stack.
Note: the ./install/
folder is not directly tied to the project so it has dedicated ./install/hie.yaml.[cbl|stack]
templates.
Using Cabal
$ cp hie-cabal.yaml hie.yaml
$ cp install/hie-cabal.yaml install/hie.yaml
Using Stack
$ cp hie-stack.yaml hie.yaml
$ cp install/hie-stack.yaml install/hie.yaml
$ cp ghcide/hie-stack.yaml ghcide/hie.yaml
$ stack build --test --no-run-tests
$ cd install
$ stack build
Using Nix
The instructions below show how to set up a Cachix binary cache and open a nix shell for local development.
$ cachix use haskell-language-server
$ nix-shell
$ cabal update
$ cabal build
If you are looking for a Nix expression to create haskell-language-server binaries, see https://github.com/haskell/haskell-language-server/issues/122
Introduction tutorial
Pepeiborra wrote an tutorial on writing a plugin in HLS.
Test your hacked HLS in your editor
If you want to test HLS while hacking on it, follow the steps below.
To do once:
- Open some codebase on which you want to test your hacked HLS in your favorite editor
- Configure this editor to use your custom HLS executable
- With Cabal:
- On Unix systems:
cabal exec which haskell-language-server
- On Windows:
cabal exec where haskell-language-server
- With Stack:
$(stack path --dist-dir)/build/haskell-language-server/haskell-language-server
To do every time you changed code and want to test it:
- Build HLS
- With Cabal:
cabal build exe:haskell-language-server
- With Stack:
stack build haskell-language-server:exe:haskell-language-server
- Restart HLS
- With VS Code:
Haskell: Restart Haskell LSP Server
Adding support for a new editor
Adding support for new editors is fairly easy if the editor already has good support for generic LSP-based extensions.
In that case, there will likely be an editor-specific support system for this (like lsp-mode
for Emacs).
This will typically provide instructions for how to support new languages.
In some cases you may need to write a small bit of additional client support, or expose a way for the user to set the server's configuration options and
for them to configure how the server is started.