A vim plugin for communicating with a language server
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The spec does not allow them, but a buggy client may send it anyway.
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README.md

Vim Language Server Client

Adds language-aware tooling to vim by communicating with a language server following the language server protocol. For more information see langserver.org.

This client has not been tested against a wide range of servers so there may be protocol bugs.

Installation

Install with your plugin management method of choice. If you don't have a preference check out vim-plug. Install a language server and ensure it is executable from your $PATH.

vim-lsc is compatible with vim 8.0, and neovim.

Configuration

Map a filetype to the command that starts the language server for that filetype in your vimrc.

let g:lsc_server_commands = {'dart': 'dart_language_server'}

To disable autocomplete in favor of manual completion also add

let g:lsc_enable_autocomplete = v:false

Most interactive features are triggered by commands, you can map keys to these commands, or use g:lsc_auto_map to have them automatically mapped for the buffers which have a language server enabled. You can use the default mappings by setting it to v:true, or specify your own mappings in a dict. The 'Complete' key will set a completion function only if g:lsc_enable_autocomplete is false.

let g:lsc_auto_map = v:true " Use defaults
" ... or set only the keys you want mapped, defaults are:
let g:lsc_auto_map = {
    \ 'GoToDefinition': '<C-]>',
    \ 'FindReferences': 'gr',
    \ 'NextReference': '<C-n>',
    \ 'PreviousReference': '<C-p>',
    \ 'FindImplementations': 'gI',
    \ 'FindCodeActions': 'ga',
    \ 'DocumentSymbol': 'go',
    \ 'WorkspaceSymbol': 'gS',
    \ 'ShowHover': 'K',
    \ 'Completion': 'completefunc',
    \}

During the initialization call LSP supports a trace argument which configures logging on the server. Set this with g:lsc_trace_level. Valid values are 'off', 'messages', or 'verbose'. Defaults to 'off'.

Features

The protocol does not require that every language server supports every feature so support may vary.

All communication with the server is asynchronous and will not block the editor. For requests that trigger an action the response might be silently ignored if it can no longer be used - you can abort most operations that are too slow by moving the cursor.

The client can be temporarily disabled for a session with LSClientDisable and re-enabled with LSClientEnable. At any time the server can be exited and restarted with LSClientRestartServer - this sends a request for the server to exit rather than kill it's process so a completely unresponsive server should be killed manually instead.

Diagnostics

Errors, warnings, and hints reported by the server are highlighted in the buffer. When the cursor is on a line with a diagnostic the message will be displayed. If there are multiple diagnostics on a line the one closest to the cursor will be displayed.

Diagnostics are also reported in the location list for each window which has the buffer open.

Autocomplete

When more than 3 word characters or a trigger character are typed a request for autocomplete suggestions is sent to the server. If the server responds before the cursor moves again the options will be provided using vim's built in completion.

Note: By default completeopt includes preview and completion items include documentation in the preview window. Close the window after completion with <c-w><c-z> or disable with set completeopt-=preview. To automatically close the documentation window use the following:

autocmd CompleteDone * silent! pclose

Disable autocomplete with let g:lsc_enable_autocomplete = v:false. When using manual completion the completefunc may have no results if completion is requested before the server responds with suggestions.

Reference Highlights

If the server supports the textDocument/documentHighlights call references to the element under the cursor throughout the document will be highlighted. Disable with let g:lsc_reference_highlights = v:false or customize the highlighting with the group lscReference. Use <c-n> (:LSClientNextReference) or <c-p> (:LSClientPReviousReference) to jump to other reference to the currently highlighted element.

Jump to definition

While the cursor is on any identifier call LSClientGoToDefinition (<C-]> if using the default mappings) to jump to the location of the definition. If the cursor moves before the server responds the response will be ignored.

Find references

While the cursor is on any identifier call LSClientFindReferences (gr if using the default mappings) to populate the quickfix list with usage locations.

Find implementations

While the cursor is on any identifier call LSClientFindImplementations (gI if using the default mappings) to populate the quickfix list with implementation locations.

Document Symbols

Call LSClientDocumentSymbol (go if using the default mappings) to populate the quickfix list with the locations of all symbols in that document.

Workspace Symbol Search

Call LSClientWorkspaceSymbol with a no arguments, or with a single String argument. (gS if using the default mappings) to query the server for symbols matching a search string. Results will populate the quickfix list.

Hover

While the cursor is on any identifier call LSClientShowHover (K if using the default mappings, bound through keywordprg) to request hover text and show it in a preview window. Override the direction of the split by setting g:lsc_preview_split_direction to either 'below' or 'above'.

Code Actions

Call LSClientFindCodeActions (ga if using the default mappings) to look for code actions available at the cursor location and run one by entering the number of the chosen action.