Haskell for Visual Studio Code

This extension adds language support for Haskell, powered by the Haskell Language Server.

Features

Warning and error diagnostics from GHC
Type information and documentation on hover
Jump to definition
Document symbols
Highlight references in document
Code completion
Formatting via Brittany, Floskell, Fourmolu, Ormolu or Stylish Haskell
Multi-root workspace support
Code evaluation (Haskell Language Server), see (Tutorial)
Integration with retrie
Code lenses for explicit import lists
Generate functions from type signatures, and intelligently complete holes using Wingman (tactics)
Integration with hlint to show diagnostics and apply hints via apply-refact
Module name suggestions for insertion or correction

Requirements

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.

Configuration options

Path to server executable executable

If your server is manually installed and not on your path, you can also manually set the path to the executable.

"haskell.serverExecutablePath": "~/.local/bin/haskell-language-server"

There are a few placeholders which will be expanded:

~, ${HOME} and ${home} will be expanded into your users' home folder.
${workspaceFolder} and ${workspaceRoot} will expand into your current project root.

Security warning

The option has resource scope so it can be changed per workspace. This supposes it could be used to execute arbitrary programs adding a .vscode/settings.json in the workspace folder including this option with the appropiate path. For this reason its scope will be changed to machine so users only will be able to change it globally. See #387 for more details.

Local documentation

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 $STACK_ROOT\config.yaml, or project's stack.yaml:
```
ghc-options:
  '$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.

Downloaded binaries

This extension will download haskell-language-server binaries to a specific location depending on your system. If you find yourself running out of disk space, you can try deleting old versions of language servers in this directory. The extension will redownload them, no strings attached.

Platform	Path
macOS	`~/Library/Application\ Support/Code/User/globalStorage/haskell.haskell/`
Windows	`%APPDATA%\Code\User\globalStorage\haskell.haskell`
Linux	`$HOME/.config/Code/User/globalStorage/haskell.haskell`

Note that if haskell-language-server-wrapper/haskell-language-server is already on the PATH, then the extension will launch it directly instead of downloading binaries.

Supported GHC versions

These are the versions of GHC that there are binaries of haskell-language-server for. Building from source may support more versions!

GHC	Linux	macOS	Windows
9.0.1 (limited)	✓	✓	✓
8.10.5	✓	✓	✓
8.10.4	✓	✓	✓
8.10.3	✓	✓	✓
8.10.2	✓	✓	✓
8.8.4	✓	✓	✓
8.8.3	✓	✓
8.8.2	✓	✓
8.6.5	✓	✓	✓
8.6.4	✓	✓	✓

The exact list of binaries can be checked in the last release of haskell-language-server: https://github.com/haskell/haskell-language-server/releases/latest

Using multi-root workspaces

First, check out what multi-root workspaces are. The idea of using multi-root workspaces, is to be able to work on several different Haskell projects, where the GHC version or stackage LTS could differ, and have it work smoothly.

The language server is now started for each workspace folder you have in your multi-root workspace, and several configurations are on a resource (i.e. folder) scope, instead of window (i.e. global) scope.

Investigating and reporting problems

Go to extensions and right click Haskell Language Server and choose Extensions Settings
Scroll down to Language Server Haskell › Trace: Server and set it to messages
Restart vscode and reproduce your problem
Go to the main menu and choose View -> Output (Ctrl + Shift + U)
On the new Output panel that opens on the right side in the drop down menu choose Haskell (<your project>)

Please include the output when filing any issues on the haskell-language-server issue tracker.

Troubleshooting

Contributing

If you want to help, get started by reading Contributing for more details.

Release Notes

See the Changelog for more details.

License

VeryMilkyJoe/vscode-haskell

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