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, this 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:

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.

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.

For 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:

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

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.