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 languages.toml files. The first is compiled into Helix and lives in the Helix repository. This provides the default configurations for languages and language servers.

You may define a languages.toml in your configuration directory which overrides values from the built-in language configuration. For example to disable auto-LSP-formatting in Rust:

# in <config_dir>/helix/languages.toml

[[language]]
name = "rust"
auto-format = false

Language configuration may also be overridden local to a project by creating a languages.toml file under a .helix directory. 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 = "  " }
language-server = { command = "mylang-lsp", args = ["--stdio"], environment = { "ENV1" = "value1", "ENV2" = "value2" } }
formatter = { command = "mylang-formatter" , args = ["--stdin"] }

These configuration keys are available:

Key	Description
name	The name of the language
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 tab-width and unit
language-server	The Language Server to run. See the Language Server configuration section below.
config	Language Server configuration
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
max-line-length	Maximum line length. Used for the :reflow command

File-type detection and the file-types key

Helix determines which language configuration to use with 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

The language-server field takes the following keys:

Key	Description
command	The name of the language server binary to execute. Binaries must be in $PATH
args	A list of arguments to pass to the language server binary
timeout	The maximum time a request to the language server may take, in seconds. Defaults to 20
language-id	The language name to pass to the language server. Some language servers support multiple languages and use this field to determine which one is being served in a buffer
environment	Any environment variables that will be used when starting the language server { "KEY1" = "Value1", "KEY2" = "Value2" }

The top-level config field is used to configure the LSP initialization options. A format sub-table within config can be used to pass extra formatting options to Document Formatting Requests. For example with typescript:

[[language]]
name = "typescript"
auto-format = true
# 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 } }

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.