Kakoune Language Server Protocol Client

kak-lsp is a Language Server Protocol client for Kakoune implemented in Rust.

Installation

Note

kak-lsp.toml destination in all described installation methods is just an example. Also, kak-lsp doesn’t read the configuration file from the current working directory or binary’s dir by default. Please consult Configuring kak-lsp to figure out where does kak-lsp expect kak-lsp.toml to be in your environment and how to specify a custom path to it. However, if you don’t need to change configuration then feel free to skip copying it anywhere as the default configuration is embedded into the kak-lsp binary.

Pre-built binaries

MacOS

Homebrew

brew install kak-lsp/kak-lsp/kak-lsp

Manual

curl -O -L https://github.com/kak-lsp/kak-lsp/releases/download/v11.0.1/kak-lsp-v11.0.1-x86_64-apple-darwin.tar.gz
tar xzvf kak-lsp-v11.0.1-x86_64-apple-darwin.tar.gz

# replace `~/.local/bin/` with something on your `$PATH`
mv kak-lsp ~/.local/bin/

mkdir -p ~/.config/kak-lsp
mv kak-lsp.toml ~/.config/kak-lsp/

Linux

Package managers

• Arch Linux: pacman -S kak-lsp or AUR/kak-lsp-git

• Void Linux: xbps-install -S kak-lsp

• Fedora Copr: sudo dnf copr enable atim/kakoune -y && sudo dnf install kak-lsp

Others

wget https://github.com/kak-lsp/kak-lsp/releases/download/v11.0.1/kak-lsp-v11.0.1-x86_64-unknown-linux-musl.tar.gz
tar xzvf kak-lsp-v11.0.1-x86_64-unknown-linux-musl.tar.gz

# replace `~/.local/bin/` with something on your `$PATH`
mv kak-lsp ~/.local/bin/

mkdir -p ~/.config/kak-lsp
mv kak-lsp.toml ~/.config/kak-lsp/

From source

Generally, you need the latest stable version of Rust to build kak-lsp.

git clone https://github.com/kak-lsp/kak-lsp
cd kak-lsp

cargo install --locked --force --path .

# replace `~/.config` with OS-specific dir as described at https://docs.rs/dirs/2.0.1/dirs/fn.config_dir.html
mkdir -p ~/.config/kak-lsp

# or just link if you are okay with default config
cp kak-lsp.toml ~/.config/kak-lsp/

With plug.kak

If you don’t mind using a plugin manager, you can install kak-lsp via plug.kak. Add this code to your kakrc:

plug "kak-lsp/kak-lsp" do %{
    cargo install --locked --force --path .
}

You can replace cargo install with ln -sf $PWD/target/release/kak-lsp ~/.local/bin/ where ~/.local/bin/ can be replaced with something in your $PATH.

Examples of configuration with plug.kak can be found at Wiki.

Language servers

kak-lsp doesn’t manage installation of language servers, please install them by yourself for the languages you plan to use kak-lsp with. Please consult the How to install servers wiki page for quick installation of language servers supported by kak-lsp out of the box.

Usage

Note

Contents below corresponds to the master branch HEAD and could be slightly out-of-sync with the version installed from pre-built binaries. The most common case is new commands being in a pre-release testing stage. Please refer to the README.asciidoc revision tagged with the version you use or the README.asciidoc from the release archive.

To enable LSP support for configured languages (see the next section) just add the following commands to your kakrc:

eval %sh{kak-lsp --kakoune -s $kak_session}  # Not needed if you load it with plug.kak.
lsp-enable

A bit more involved but recommended way is to enable kak-lsp only for specific filetypes you need via lsp-enable-window, e.g.:

eval %sh{kak-lsp --kakoune -s $kak_session}  # Not needed if you load it with plug.kak.
hook global WinSetOption filetype=(rust|python|go|javascript|typescript|c|cpp) %{
    lsp-enable-window
}

Either way you get:

• completions

• lsp-definition command to go to definition, mapped to gd by default

• lsp-hover command to show hover info (including relevant diagnostics when available) in the info box.

  • lsp-hover-buffer command to show the same in a scratch buffer.

  • to automatically show hover when you move around, use lsp-auto-hover-enable

  • to show hover anchored to hovered position, use set global lsp_hover_anchor true

  • to exclude diagnostics, use set-option global lsp_show_hover_format 'printf %s "${lsp_info}"'

• lsp-declaration command to jump to the declaration of the symbol under the main cursor

• lsp-definition command to jump to the definition of the symbol under the main cursor

• lsp-type-definition command to jump to the definition of the type of the symbol under the main cursor

• lsp-implementation command to find implementations for the symbol under the main cursor

• lsp-references command to find references to the symbol under the main cursor, mapped to gr by default

  • for the previous five commands, the *goto* buffer has filetype lsp-goto, so you can press <ret> on a line or use the lsp-jump command

• lsp-find-error command to jump to the next or previous error in the current file

• lsp-next-location and lsp-previous-location to jump to the next or previous location listed in a buffer with the lsp-goto filetype. These also work for buffers *grep*, *lint* and *make*

• lsp-highlight-references command to highlight all references to the symbol under the main cursor in the current buffer with the Reference face (which is equal to the MatchingChar face by default)

• lsp-document-symbol command to list the current buffer’s symbols

• lsp-workspace-symbol command to list project-wide symbols matching the query

• lsp-workspace-symbol-incr command to incrementally list project-wide symbols matching the query

  • *symbols* buffer has filetype lsp-goto so you can press <ret> on a line or use the lsp-jump command

• lsp-diagnostics command to list project-wide diagnostics (current buffer determines project and language to collect diagnostics for)

  • *diagnostics* buffer has filetype lsp-goto so you can press <ret> on a line or use the lsp-jump command

• lsp-incoming-calls and lsp-outgoing-calls commands to list callers and callees of the function at the cursor.

  • *callers* and *callees* buffers have filetype lsp-goto so you can press <ret> on a line or use the lsp-jump command

• inline diagnostics highlighting using the DiagnosticError, DiagnosticHint, DiagnosticInfo and DiagnosticWarning faces; can be disabled with lsp-inline-diagnostics-disable command

• flags in the left margin on lines with errors or other diagnostics; can be disabled with lsp-diagnostic-lines-disable command

• lsp-formatting command to format current buffer, according to the tabstop and lsp_insert_spaces options

• lsp-formatting-sync command to format current buffer synchronously, suitable for use with BufWritePre hook:

• lsp-next-symbol and lsp-previous-symbol command to go to the buffer’s next and current/previous symbol.

• lsp-hover-next-symbol and lsp-hover-previous-symbol to show hover of the buffer’s next and current/previous symbol.

hook global WinSetOption filetype=rust %{
    hook window BufWritePre .* lsp-formatting-sync
}

• lsp-rename <new_name> and lsp-rename-prompt commands to rename the symbol under the main cursor.

• If lsp_auto_show_code_actions is true, a lightbulb in the mode line whenever code actions are available at the main cursor position

  • To customize the lightbulb, you can override lsp-show-code-actions and lsp-hide-code-actions

• lsp-code-actions to open a menu to choose a code action to run

  • To customize the menu, you can override lsp-perform-code-action

• lsp-code-action to run the code action matching the given pattern.

• lsp_diagnostic_error_count, lsp_diagnostic_hint_count, lsp_diagnostic_info_count and lsp_diagnostic_warning_count options which contain the number of diagnostics of the respective level for the current buffer. For example, you can put it into your modeline to see at a glance if there are errors in the current file

• starting new kak-lsp session when Kakoune session begins and stopping it when Kakoune session ends

Note

By default, kak-lsp exits when it doesn’t receive any request from Kakoune for 30 minutes, even if the Kakoune session is still up and running. Change server.timeout in kak-lsp.toml to tweak this duration, or set it to 0 to disable this behavior. In any scenario, a new request would spin up a fresh server if it is down.

• lsp user mode. The following example mapping gives you access to the shortcuts from below table after typing ,l.

map global user l %{: enter-user-mode lsp<ret>} -docstring "LSP mode"

Binding	Command
a	lsp-code-actions
c	lsp-capabilities
d	lsp-definition
e	lsp-diagnostics
f	lsp-formatting
h	lsp-hover
i	lsp-implementation
j	lsp-outgoing-calls
k	lsp-incoming-calls
r	lsp-references
R	lsp-rename-prompt
s	lsp-signature-help
S	lsp-document-symbol
o	lsp-workspace-symbol-incr
n	lsp-find-error
p	lsp-find-error --previous
y	lsp-type-definition
9	lsp-hover-previous-function
0	lsp-hover-next-function
&	lsp-highlight-references
(	lsp-previous-function
)	lsp-next-function
[	lsp-hover-previous-symbol
]	lsp-hover-next-symbol
{	lsp-previous-symbol
}	lsp-next-symbol

To know which subset of kak-lsp commands is backed by the current buffer’s filetype’s language server use lsp-capabilities command.

All commands are also represented as subcommands of the lsp umbrella command if you prefer this style. For example, you can use lsp references instead of lsp-references.

Configuration

kak-lsp itself has configuration, but it also adds configuration options to Kakoune that affect the Kakoune integration.

Configuring kak-lsp

kak-lsp is configured via a configuration file in TOML format. By default kak-lsp tries to read kak-lsp/kak-lsp.toml under OS-specific config dir as described here, but you can override it with command-line option --config. Look into the default kak-lsp.toml, it should be quite self-explanatory.

Important: The configuration file does not extend the default configuration, but rather overrides it. This means that if you want to customize any of the configuration, you must copy the entire default configuration and then edit it.

In the language section of kak-lsp.toml, the roots parameter is a list of file globs. Whenever your editor session wants to send an LSP request, the first glob that matches a file in any of the current buffer’s parent directories will cause kak-lsp to set the project root to that parent directory.

You can define an environment variable like KAK_LSP_PROJECT_ROOT_RUST=/my/project to always use /my/project as root for Rust files inside /my/project. Substitute RUST with another language ID to do the same for other file types.

The environment variable KAK_LSP_FORCE_PROJECT_ROOT=/my/project will make kak-lsp always use /my/project as project root, even for files outside this directory. This avoids starting separate language servers for files outside /my/project, and ensures that your language server is aware of your project’s build configuration even when navigating library code.

If you are setting any server options via cli, do not forget to append them to %sh{kak-lsp --kakoune …​} in your kakrc. It’s not needed if you change options in ~/.config/kak-lsp/kak-lsp.toml.

Please let us know if you have any ideas about how to make the default config more sensible.

Server-specific configuration

Many servers accept configuration options that are not part of the LSP spec. The TOML table [language.<filetype>.settings] holds those configuration options. It has the same structure as the corresponding fragments from VSCode’s settings.json. For example:

[language.go]
...
settings_section = "gopls"
[language.go.settings.gopls]
"formatting.gofumpt" = true

During server initialization, kak-lsp sends the section specified by settings_section; in this case {"formatting.gofumpt":true}. Whenever you change the Kakoune option lsp_config, the same section is sent via workspace/didChangeConfiguration. Additionally, kak-lsp will send arbitrary sections that are requested by the server in workspace/configuration.

Configuring Kakoune

kak-lsp’s Kakoune integration declares the following options:

• lsp_completion_trigger (str): This option is set to a Kakoune command, which is executed every time the user pauses in insert mode. If the command succeeds, kak-lsp will send a completion request to the language server.

• lsp_diagnostic_line_error_sign, lsp_diagnostic_line_hint_sign, lsp_diagnostic_line_info_sign, and lsp_diagnostic_line_warning_sign (str): When using lsp-diagnostic-lines-enable and the language server detects an error or another diagnostic, kak-lsp will add a flag to the left-most column of the window, using this string and one of the corresponding faces LineFlagError, LineFlagHint, LineFlagInfo or LineFlagWarning.

• lsp_hover_anchor (bool): When using lsp-hover or lsp-auto-hover-enable, if this option is true then the hover information will be displayed next to the active selection. Otherwise, the information will be displayed in a box in the lower-right corner.

• lsp_hover_max_lines (int): If greater than 0 then limit rendered hover information to the given number of lines.

• lsp_hover_insert_mode_trigger (str): This option is set to a Kakoune command. When using lsp-auto-hover-insert-mode-enable, this command is executed every time the user pauses in insert mode. If the command succeeds, kak-lsp will send a hover-information request for the text selected by the command.

• lsp_insert_spaces (bool): When using lsp-formatting, if this option is true, kak-lsp will ask the language server to indent with spaces rather than tabs.

• lsp_auto_highlight_references (bool): If this option is true then lsp-highlight-references is executed every time the user pauses in normal mode.

• lsp_auto_show_code_actions (bool): If this option is true then lsp-code-actions is executed every time the user pauses in normal mode.

• lsp_config (str): This is a TOML string of the same format as kak-lsp.toml, except it only supports one settings:

  • [language.<filetype>.settings]: this works just like the static configuration of the same name in kak-lsp.toml, see the section about server-specific configuration. This will override the static configuration of the given language.

For example, you can toggle an option dynamically with a command like this:

set-option global lsp_config %{
    [language.go.settings.gopls]
    "formatting.gofumpt" = true
}

Inlay hints for rust-analyzer

Inlay hints are a feature supported by rust-analyzer, which show inferred types, parameter names in function calls, and the types of chained calls inline in the code. To enable support for it in kak-lsp, add the following to your kakrc:

hook global WinSetOption filetype=rust %{
  hook window -group rust-inlay-hints BufReload .* rust-analyzer-inlay-hints
  hook window -group rust-inlay-hints NormalIdle .* rust-analyzer-inlay-hints
  hook window -group rust-inlay-hints InsertIdle .* rust-analyzer-inlay-hints
  hook -once -always window WinSetOption filetype=.* %{
    remove-hooks window rust-inlay-hints
  }
}

You can change the hints' face with set-face global InlayHint <face>.

Semantic Tokens

kak-lsp supports the semanticTokens feature for semantic highlighting. If the language server supports it, you can enable it with:

hook global WinSetOption filetype=<language> %{
  hook window -group semantic-tokens BufReload .* lsp-semantic-tokens
  hook window -group semantic-tokens NormalIdle .* lsp-semantic-tokens
  hook window -group semantic-tokens InsertIdle .* lsp-semantic-tokens
  hook -once -always window WinSetOption filetype=.* %{
    remove-hooks window semantic-tokens
  }
}

The faces used for semantic tokens and modifiers can be modified in kak-lsp.toml, under the semantic_tokens section. The syntax for such an entry is

[[semantic_tokens]]
token = "variable"
face = "const_variable_declaration"
modifiers = ["constant", "declaration"]

where token is the token’s name as reported by the language server (see lsp-capabilities), face is the face that will be applied in Kakoune (you’ll want to define these in your theme/config) and modifiers is an array of modifier names (also reported by the language server). modifiers may be omitted, but token and face are required.

You may create any arbitrary number of definitions with permutations between the token names and modifiers reported by the server. For an entry to match a token, all the entry’s modifiers must exist on the token. However, the token may have additional modifiers not assigned in the config entry.
kak-lsp will find the most specific matching configuration to apply, where specificity is defined as the number of matching modifiers. If multiple matching entries have the same number of modifiers, the one that was defined last in the configuration wins.

Example:

Assuming the following configuration,

[[semantic_tokens]]
token = "variable"
face = "const_variable_declaration"
modifiers = ["constant", "declaration"]

[[semantic_tokens]]
token = "variable"
face = "const_variable"
modifiers = ["constant"]

[[semantic_tokens]]
token = "variable"
face = "variable"

kak-lsp will perform these mappings:

Token	Modifiers	Face	Comment
variable	constant, declaration	const_variable_declaration	First entry matches with 2 modifiers.
variable	constant	const_variable	First and second entry match with 1 modifier, second wins.
variable	declaration	variable	Only third entry matches. First entry doesn’t match, because constant is missing.
variable		variable	Third entry matches.
function			No entries match and no face is applied.

Inlay Diagnostics

kak-lsp supports showing diagnostics inline after their respective line, but this behavior can be somewhat buggy and must be enabled explicitly:

lsp-inlay-diagnostics-enable global

Markdown rendering in info box

kak-lsp shows some additional information provided by the language server in an info box. This information includes documentation for the token under the cursor (lsp-hover) and documentation for completion candidates. In both cases, the Language Server Protocol allows for both plain text and Markdown, and most servers do implement Markdown.

To make use of Markdown, kak-lsp transpiles it into Kakoune’s markup language, utilizing various faces for styling. These faces all default to the Information face, to ensure that the text in the info box works with any color scheme.

To enable Markdown highlighting, define some of the following faces in your theme or kakrc:

Face	Usage
InfoDefault	The default text color. You’ll likely want to leave this at the default Information.
InfoBlock	The face used for code blocks. Language specific syntax highlighting for code blocks is not supported.
InfoBlockQuote	The face used for block quotes. The > Markdown syntax is still rendered.
InfoBullet	The face used to highlight the list symbol for both ordered and unordered lists. For list items' text, InfoDefault is used.
InfoHeader	The face used for headings. There is currently no distinction between different heading levels.
InfoLink	The face used to highlight link titles. Maybe some classic blue+u for this one?
InfoLinkMono	This face is assigned to inline code spans within link titles, such as in the following Markdown snippet. Here, the word format will receive the InfoLinkMono face. [the `format` function](https://example.com)
InfoMono	The face used for inline code spans (backtick strings).
InfoRule	The face used for horizontal lines (rules).
InfoDiagnosticError	Used for error messages in the diagnostics inside hover info. This defaults to Kakoune’s built-in Error face.
InfoDiagnosticHint	Used for hints in the diagnostics inside hover info.
InfoDiagnosticInformation	Used for informational messages in the diagnostics inside hover info.
InfoDiagnosticWarning	Used for warnings in the diagnostics inside hover info.

For convenience, here is a snippet to paste into your theme/config:

face global InfoDefault               Information
face global InfoBlock                 Information
face global InfoBlockQuote            Information
face global InfoBullet                Information
face global InfoHeader                Information
face global InfoLink                  Information
face global InfoLinkMono              Information
face global InfoMono                  Information
face global InfoRule                  Information
face global InfoDiagnosticError       Information
face global InfoDiagnosticHint        Information
face global InfoDiagnosticInformation Information
face global InfoDiagnosticWarning     Information

Current limitations of this feature are:

• Language specific syntax highlighting for code blocks is not supported.

• For hyperlinks, only their title (the pretty name) is shown.

• The original syntax for headings is retained to visualize their level.

Snippets

kak-lsp has experimental support for snippets. It is enabled by setting snippet_support = true at the top level of the config.

It uses the two faces SnippetsNextPlaceholders and SnippetsOtherPlaceholders, you may want to customize those.

To properly use snippets, you’ll probably want something like this:

def -hidden insert-c-n %{
 try %{
   lsp-snippets-select-next-placeholders
   exec '<a-;>d'
 } catch %{
   exec -with-hooks '<c-n>'
 }
}
map global insert <c-n> "<a-;>: insert-c-n<ret>"

This maps <c-n> to select the next placeholder if there is one, and otherwise executes <c-n> as normal

Limitations

Encoding

kak-lsp works only with UTF-8 documents.

Position.character interpretation

Currently, kak-lsp doesn’t conform to the spec regarding the interpretation of Position.character. LSP spec says that

A position inside a document (see Position definition below) is expressed as a zero-based line and character offset. The offsets are based on a UTF-16 string representation. So for a string of the form a𐐀b the character offset of the character a is 0, the character offset of 𐐀 is 1 and the character offset of b is 3 since 𐐀 is represented using two code units in UTF-16.

However, kak-lsp treats Position.character as an offset in UTF-8 code points by default. Fortunately, it appears to produce the same result within the Basic Multilingual Plane (BMP) which includes a lot of characters.

Unfortunately, many language servers violate the spec as well, and in an inconsistent manner. Please refer microsoft/language-server-protocol#376 for more information. There are two main types of violations we met in the wild:

1) Using UTF-8 code points, just like kak-lsp does. Those should work well with kak-lsp for characters outside BMP out of the box.

2) Using UTF-8 code units (bytes), just like Kakoune does. Those are supported by kak-lsp but require adding offset_encoding = "utf-8" to the language server configuration in kak-lsp.toml.

Troubleshooting

If kak-lsp fails try to put this line in your kakrc after kak-lsp --kakoune invocation:

set global lsp_cmd "kak-lsp -s %val{session} -vvv --log /tmp/kak-lsp.log"

to enable debug logging.

If it does not give enough insight to fix the problem or if the problem is a bug in kak-lsp itself please don’t hesitate to raise an issue.

Default configuration

Please also try to reproduce the issue with a minimal configuration. Sometimes the problem occurs only with specific settings in your ~/.config/kak-lsp/kak-lsp.toml and/or ~/.config/kak/. Use this command to start Kakoune with kak-lsp enabled, both with pristine settings.

HOME=$(mktemp -d) kak -e '
    eval %sh{kak-lsp --kakoune -s $kak_session}
    set global lsp_cmd "kak-lsp -s %val{session} -vvvv --log /tmp/kak-lsp.log"
    lsp-enable'

Note	Some Kakoune plugins could interfere with kak-lsp, particularly completions providers. E.g. racer.kak competes for autocompletion in Rust files.

Crashes

For troubleshooting crashes, you might like to run kak-lsp outside of Kakoune.

To do this:

1. Before launching Kakoune, run kak-lsp with an arbitrary session ID (here foobar):

   kak-lsp -s foobar

2. In a second terminal, run Kakoune with the same session ID:

   kak -s foobar

Versioning

kak-lsp follows SemVer with one notable difference from common practice: we don’t use 0 major version to indicate that product is not yet reached stability. Even for non-stable and not feature-complete product user should be clearly informed about breaking change. Therefore we start with major version 1 and increment it each time when upgrade requires user’s attention.