F# support for Vim/Neovim

Part of the Ionide plugin suite.

• A fork of fsharp/vim-fsharp.

• Uses LSP-mode of FsAutoComplete as a backend.

• Uses one of the following LSP clients:

  • Neovim's built-in LSP client (requires Neovim 0.5 )
  • autozimu/LanguageClient-neovim.

Consider this to be beta since it's lacking features compared to Ionide-VSCode and not as battle-tested as that.

That being said, we maintainers use this plugin daily so it will someday become feature-rich and stable for sure.

Feel free to request features and/or file bug reports!

• Neovim or Vim 8

• .NET Core SDK

  • Required to install and run FsAutoComplete.
  • Very useful for command-line development.

• If you are using Vim or Neovim below version 0.5:

  • autozimu/LanguageClient-neovim
    • Required to communicate with FsAutoComplete.
  • junegunn/fzf (optional)
    • Optional dependency of LanguageClient-neovim.
    • Multi-entry selection UI.

• Syntax highlighting
• Auto completions
• Error highlighting, error list, and quick fixes based on errors
• Tooltips
• Codelens
• Go to Definition
• Find all references
• Highlighting usages
• Rename
• Show symbols in file
• Find symbol in workspace
• Show signature in status line
• Integration with F# Interactive
• Integration with FSharpLint (additional hints and quick fixes)
• Integration with Fantomas (the best formatter available for F#)

Install FsAutoComplete with dotnet tool install.

If you want to install it as a "global" tool, run dotnet tool install -g fsautocomplete.

If you want to install it as a project-local tool, run dotnet tool install fsautocomplete at the root directory of your F# project, and configure g:fsharp#fsautocomplete_command as explained here.

No LSP client plugin is required.

If you are using neovim/nvim-lspconfig, do not enable fsautocomplete. Ionide-vim automatically integrates itself into nvim-lspconfig and will register itself as a server.

Install LanguageClient-neovim. Refer to their INSTALL.md.

Here is the example for vim-plug package manager.

Plug 'autozimu/LanguageClient-neovim', {
    \ 'branch': 'next',
    \ 'do': 'bash install.sh',
    \ }

If you are running Windows, you will have to set the value of do to 'powershell -ExecutionPolicy Unrestricted .\install.ps1'.

We recommend using hrsh7th/nvim-cmp, but the setup is a bit complicated. See the example in our wiki for how to setup nvim-cmp to be used with Ionide-vim.

Shougo/deoplete.nvim is an easier alternative, but they say its development is complete and it won't get some features such as heredoc.

" if you use nvim > 0.5:
Plug 'Shougo/deoplete.nvim', { 'do': ':UpdateRemotePlugins' }
Plug 'deoplete-plugins/deoplete-lsp'

" otherwise:
Plug 'Shougo/deoplete.nvim'
Plug 'roxma/nvim-yarp'
Plug 'roxma/vim-hug-neovim-rpc'

" also set this in both cases.
let g:deoplete#enable_at_startup = 1

Plug 'ionide/Ionide-vim'

call dein#add('ionide/Ionide-vim')

Clone Ionide-vim to some runtimepath.

Opening either *.fs, *.fsi or *.fsx files should trigger syntax highlighting and other depending runtime files as well.

Ionide-vim only handles F# specific features of FsAutoComplete, and any other generic features such as "go to definition" and "rename" are provided by either Neovim or autozimu/LanguageClient-neovim.

You should set your key bindings for those features on your own, so please refer to their documentation. The examples in our wiki also contains an example bindings for both Neovim and LanguageClient-neovim.

To be added as requested for F#-specific features.

• Shows the projects currently loaded.

• Loads specified projects (sln or fsproj).

• Reloads all the projects currently loaded.
• Automatically called when you save .fsproj files. Can be disabled in settings.

• Updates FSAC configuration.
• See FsAutoComplete Settings for details.

Ionide-vim has an integration with F# Interactive.

FSI is displayed using the builtin :terminal feature introduced in Vim 8 / Neovim and can be used like in VSCode.

• Shows a F# Interactive window.

• Evaluates given expression in FSI.

• Sends the content of current file to FSI.

• Resets the current FSI session.

• When in normal mode, sends the current line to FSI.
• When in visual mode, sends the selection to FSI.
• Sending code to FSI opens FSI window but the cursor does not focus to it. Unlike Neovim, Vim doesn't support asynchronous buffer updating so you have to input something (e.g. moving cursor) to see the result. You can change this behavior in settings.

• Toggles FSI window. FSI windows shown in different tabpages share the same FSI session.
• When opened, the cursor automatically focuses to the FSI window (unlike in Alt-Enter by default).

You can customize the location of FSI, key mappings, etc. See the documentation below.

To be added as requested for F#-specific features.

See some examples in our wiki if you're not sure what you would want to set.

Set g:fsharp#backend to

• nvim if you want to use neovim's built-in LSP client.
• languageclient-neovim if you want to use autozimu/LanguageClient-neovim.
• disable if you only want the syntax highlighting and the FSI integration.

Default: nvim if you are using Neovim 0.5 , languageclient-neovim otherwise.

let g:fsharp#backend = "languageclient-neovim"

Default: ['fsautocomplete', '--background-service-enabled']

This option overrides the path to the FSAC Ionide-vim uses.

By default, Ionide-vim uses the FSAC installed globally with dotnet tool install.

For example, if you want to use a project-local FSAC, set the following:

let g:fsharp#fsautocomplete_command =
    \ [ 'dotnet',
    \   'fsautocomplete',
    \   '--background-service-enabled'
    \ ]

Note: You have to use an array here. Setting a string value to this option will result in an error.

Default: not set

Ionide-vim does not provide default keybindings for various LSP features, so you will have to set them yourself.

• If you are using neovim's built-in LSP client, see here.
• If you are using LanguageClient-neovim, refer to their docs.

Examples are available at our wiki.

Default: enabled

Neovim's LSP client comes with no default colorscheme, so Ionide-vim sets a VSCode-like one for LSP diagnostics by default. You can disable this by the following:

let g:fsharp#lsp_recommended_colorscheme = 0

Default: enabled

With nvim-lspconfig, you would manually call the setup function for each LSP servers. Ionide-vim does this automatically by default, but you can disable it.

let g:fsharp#lsp_auto_setup = 0

lua << EOF
require'ionide'.setup{}
EOF

Default: enabled

By default, Ionide-vim sets the following so that CodeLens gets refreshed automatically.

augroup FSharp_AutoRefreshCodeLens
    autocmd!
    autocmd CursorHold,InsertLeave <buffer> lua vim.lsp.codelens.refresh()
augroup END

You can disable this by setting the below option:

let g:fsharp#lsp_codelens = 0

Note: this setting does not affect LanguageClient-neovim's CodeLens feature. Please see their docs for how to configure it.

• Ionide-vim uses snake_case for the setting names.
  • For FSAC settings only, CamelCase can also be used (as it gets serialized to a F# record).
  • If both snake_case and CamelCase are specified, the snake_case one will be preferred.
• You can change the values at runtime and then notify the changes to FSAC by :FSharpUpdateServerConfig.
• Some of the settings may not work in Ionide-vim as it is lacking the corresponding feature of Ionide-VSCode.
• If not specified, the recommended default values described in the FSAC's documentation will be used.
  • You can disable this by let g:fsharp#use_recommended_server_config = 0.

See the documentation of FSAC for the complete list of available settings. Frequently used ones are:

Default: enabled

let g:fsharp#automatic_workspace_init = 1 " 0 to disable.

Default: 2

let g:fsharp#workspace_mode_peek_deep_level = 2

Default: empty

let g:fsharp#exclude_project_directories = ['paket-files']

Default: all enabled

You may want to bind LanguageClient#textDocument_codeAction() to some shortcut key. Refer to their docs.

" 0 to disable.
let g:fsharp#linter = 1
let g:fsharp#unused_opens_analyzer = 1
let g:fsharp#unused_declarations_analyzer = 1

Default: enabled

let g:fsharp#automatic_reload_workspace = 1 " 0 to disable.

Default: disabled

let g:fsharp#show_signature_on_cursor_move = 0 " 1 to enable.

Note: this feature is known to be causing issues in some circumstances (#57, #58). So this feature is now disabled by default.

Default: dotnet fsi

If you want to use a .NET Framework FSI instead of .NET Core one, set g:fsharp#use_sdk_scripts to 0. See: ionide/FsAutoComplete#466 (comment)

let g:fsharp#fsi_command = "fsharpi"
let g:fsharp#use_sdk_scripts = 0 " for net462 FSI

Default: --readline-

Sets additional arguments of the FSI instance Ionide-vim spawns and changes the behavior of FSAC accordingly when editing fsx files. FSAC passes parameters on to the compiler for static analysis of script files. Not all parameters are shared between the compiler and interpreter, so FSAC splits these into

1. FSIExtraInteractiveParameters: specifically for use with the interpreter process
2. FSIExtraSharedParameters: those parameters which should be passed both to the interactive interpreter and the compiler

Ionide-vim will pass all options from both of these parameters to the interpreter launched by fsharp#fsi_command

let g:fsharp#fsi_extra_interactive_parameters = ['--readline-']
let g:fsharp#fsi_extra_shared_parameters = ['--langversion:preview']

There is a legacy option that is still supported by Ionide-vim and FSAC, FSIExtraParameters, that will be deprecated upstream in the future. This is a single option that combines the functionality of both mentioned above. Using interactive-only parameters in this option yields compiler errors. See more discussion in the issue for FSAC.

It is recommended to migrate configuration to the new parameters. If you are currently using FSIExtraParameters, simply copying the options to FSIExtraSharedParameters will preserve all current behavior.

Unti

Default: botright 10new

It must create a new empty window and then focus to it.

See :help opening-window for details.

let g:fsharp#fsi_window_command = "botright vnew"

Default: disabled

If you are using Vim, you might want to enable this to see the result without inputting something.

let g:fsharp#fsi_focus_on_send = 1 " 0 to not to focus.

Default: vscode

• vscode: Default. Same as in Ionide-VSCode (Alt-Enter to send, Alt-@ to toggle terminal).
  • <M-CR> in Neovim / <ESC><CR> in Vim: Sends line/selection to FSI.
  • <M-@> in Neovim / <ESC>@ in Vim: Toggles FSI window.
• vim-fsharp: Same as in fsharp/vim-fsharp. Note that <leader> is mapped to backslash by default. See :help mapleader.
  • <leader>i : Sends line/selecion to FSI.
  • <leader>e : Toggles FSI window.
• custom: You must set both g:fsharp#fsi_keymap_send and g:fsharp#fsi_keymap_toggle by yourself.
  • g:fsharp#fsi_keymap_send : Sends line/selection to FSI.
  • g:fsharp#fsi_keymap_toggle : Toggles FSI window.
• none: Disables mapping.

" custom mapping example
let g:fsharp#fsi_keymap = "custom"
let g:fsharp#fsi_keymap_send   = "<C-e>"
let g:fsharp#fsi_keymap_toggle = "<C-@>"

Linting (other than the basic ones described above) and formatting is powered by independent tools, FSharpLint and Fantomas respectively.

Both uses their own JSON file for configuration and Ionide-vim does not control them. See their docs about configuration: FSharpLint and Fantomas.

If you are using neovim 0.4.0 or later, floating windows will be used for tooltips and you might find it convenient to make them appear if the cursor does not move for several seconds.

if has('nvim') && exists('*nvim_open_win')
  augroup FSharpShowTooltip
    autocmd!
    autocmd CursorHold *.fs,*.fsi,*.fsx call fsharp#showTooltip()
  augroup END
endif

Note that you can set the delay time to show the tooltip by set updatetime=<ms>. The default delay is 4 seconds, which you may find too slow.

• The primary maintainer for this repository is @cannorin.