helix/book/src/languages.md

Languages

Language-specific settings and settings for language servers are configured in languages.toml files.

languages.toml files

There are three possible locations for a languages.toml file:

1. In the Helix source code, which lives in the Helix repository. It provides the default configurations for languages and language servers.

2. In your configuration directory. This overrides values from the built-in language configuration. For example, to disable auto-LSP-formatting in Rust:

   # in <config_dir>/helix/languages.toml
   
   [language-server.mylang-lsp]
   command = "mylang-lsp"
   
   [[language]]
   name = "rust"
   auto-format = false
   

3. In a .helix folder in your project. Language configuration may also be overridden local to a project by creating a languages.toml file in a .helix folder. Its settings will be merged with the language configuration in the configuration directory and the built-in configuration.

Language configuration

Each language is configured by adding a [[language]] section to a languages.toml file. For example:

[[language]]
name = "mylang"
scope = "source.mylang"
injection-regex = "mylang"
file-types = ["mylang", "myl"]
comment-token = "#"
indent = { tab-width = 2, unit = "  " }
formatter = { command = "mylang-formatter" , args = ["--stdin"] }
language-servers = [ "mylang-lsp" ]

These configuration keys are available:

Key	Description
name	The name of the language
language-id	The language-id for language servers, checkout the table at TextDocumentItem for the right id
scope	A string like source.js that identifies the language. Currently, we strive to match the scope names used by popular TextMate grammars and by the Linguist library. Usually source.<name> or text.<name> in case of markup languages
injection-regex	regex pattern that will be tested against a language name in order to determine whether this language should be used for a potential language injection site.
file-types	The filetypes of the language, for example ["yml", "yaml"]. See the file-type detection section below.
shebangs	The interpreters from the shebang line, for example ["sh", "bash"]
roots	A set of marker files to look for when trying to find the workspace root. For example Cargo.lock, yarn.lock
auto-format	Whether to autoformat this language when saving
diagnostic-severity	Minimal severity of diagnostic for it to be displayed. (Allowed values: Error, Warning, Info, Hint)
comment-token	The token to use as a comment-token
indent	The indent to use. Has sub keys unit (the text inserted into the document when indenting; usually set to N spaces or "\t" for tabs) and tab-width (the number of spaces rendered for a tab)
language-servers	The Language Servers used for this language. See below for more information in the section Configuring Language Servers for a language
grammar	The tree-sitter grammar to use (defaults to the value of name)
formatter	The formatter for the language, it will take precedence over the lsp when defined. The formatter must be able to take the original file as input from stdin and write the formatted file to stdout
soft-wrap	editor.softwrap
text-width	Maximum line length. Used for the :reflow command and soft-wrapping if soft-wrap.wrap-at-text-width is set, defaults to editor.text-width
workspace-lsp-roots	Directories relative to the workspace root that are treated as LSP roots. Should only be set in .helix/config.toml. Overwrites the setting of the same name in config.toml if set.
persistent-diagnostic-sources	An array of LSP diagnostic sources assumed unchanged when the language server resends the same set of diagnostics. Helix can track the position for these diagnostics internally instead. Useful for diagnostics that are recomputed on save.

File-type detection and the file-types key

Helix determines which language configuration to use based on the file-types key from the above section. file-types is a list of strings or tables, for example:

file-types = ["Makefile", "toml", { suffix = ".git/config" }]

When determining a language configuration to use, Helix searches the file-types with the following priorities:

1. Exact match: if the filename of a file is an exact match of a string in a file-types list, that language wins. In the example above, "Makefile" will match against Makefile files.
2. Extension: if there are no exact matches, any file-types string that matches the file extension of a given file wins. In the example above, the "toml" matches files like Cargo.toml or languages.toml.
3. Suffix: if there are still no matches, any values in suffix tables are checked against the full path of the given file. In the example above, the { suffix = ".git/config" } would match against any config files in .git directories. Note: / is used as the directory separator but is replaced at runtime with the appropriate path separator for the operating system, so this rule would match against .git\config files on Windows.

Language Server configuration

Language servers are configured separately in the table language-server in the same file as the languages languages.toml

For example:

[language-server.mylang-lsp]
command = "mylang-lsp"
args = ["--stdio"]
config = { provideFormatter = true }
environment = { "ENV1" = "value1", "ENV2" = "value2" }

[language-server.efm-lsp-prettier]
command = "efm-langserver"

[language-server.efm-lsp-prettier.config]
documentFormatting = true
languages = { typescript = [ { formatCommand ="prettier --stdin-filepath ${INPUT}", formatStdin = true } ] }

These are the available options for a language server.

Key	Description
command	The name or path of the language server binary to execute. Binaries must be in $PATH
args	A list of arguments to pass to the language server binary
config	LSP initialization options
timeout	The maximum time a request to the language server may take, in seconds. Defaults to 20
environment	Any environment variables that will be used when starting the language server { "KEY1" = "Value1", "KEY2" = "Value2" }

A format sub-table within config can be used to pass extra formatting options to Document Formatting Requests. For example, with typescript:

[language-server.typescript-language-server]
# pass format options according to https://github.com/typescript-language-server/typescript-language-server#workspacedidchangeconfiguration omitting the "[language].format." prefix.
config = { format = { "semicolons" = "insert", "insertSpaceBeforeFunctionParenthesis" = true } }

Configuring Language Servers for a language

The language-servers attribute in a language tells helix which language servers are used for this language.

They have to be defined in the [language-server] table as described in the previous section.

Different languages can use the same language server instance, e.g. typescript-language-server is used for javascript, jsx, tsx and typescript by default.

In case multiple language servers are specified in the language-servers attribute of a language, it's often useful to only enable/disable certain language-server features for these language servers.

As an example, efm-lsp-prettier of the previous example is used only with a formatting command prettier, so everything else should be handled by the typescript-language-server (which is configured by default). The language configuration for typescript could look like this:

[[language]]
name = "typescript"
language-servers = [ { name = "efm-lsp-prettier", only-features = [ "format" ] }, "typescript-language-server" ]

or equivalent:

[[language]]
name = "typescript"
language-servers = [ { name = "typescript-language-server", except-features = [ "format" ] }, "efm-lsp-prettier" ]

Each requested LSP feature is prioritized in the order of the language-servers array. For example, the first goto-definition supported language server (in this case typescript-language-server) will be taken for the relevant LSP request (command goto_definition). The features diagnostics, code-action, completion, document-symbols and workspace-symbols are an exception to that rule, as they are working for all language servers at the same time and are merged together, if enabled for the language. If no except-features or only-features is given, all features for the language server are enabled. If a language server itself doesn't support a feature, the next language server array entry will be tried (and so on).

The list of supported features is:

• format
• goto-definition
• goto-declaration
• goto-type-definition
• goto-reference
• goto-implementation
• signature-help
• hover
• document-highlight
• completion
• code-action
• workspace-command
• document-symbols
• workspace-symbols
• diagnostics
• rename-symbol
• inlay-hints

Tree-sitter grammar configuration

The source for a language's tree-sitter grammar is specified in a [[grammar]] section in languages.toml. For example:

[[grammar]]
name = "mylang"
source = { git = "https://github.com/example/mylang", rev = "a250c4582510ff34767ec3b7dcdd3c24e8c8aa68" }

Grammar configuration takes these keys:

Key	Description
name	The name of the tree-sitter grammar
source	The method of fetching the grammar - a table with a schema defined below

Where source is a table with either these keys when using a grammar from a git repository:

Key	Description
git	A git remote URL from which the grammar should be cloned
rev	The revision (commit hash or tag) which should be fetched
subpath	A path within the grammar directory which should be built. Some grammar repositories host multiple grammars (for example tree-sitter-typescript and tree-sitter-ocaml) in subdirectories. This key is used to point hx --grammar build to the correct path for compilation. When omitted, the root of repository is used

Choosing grammars

You may use a top-level use-grammars key to control which grammars are fetched and built when using hx --grammar fetch and hx --grammar build.

# Note: this key must come **before** the [[language]] and [[grammar]] sections
use-grammars = { only = [ "rust", "c", "cpp" ] }
# or
use-grammars = { except = [ "yaml", "json" ] }

When omitted, all grammars are fetched and built.