helix-plus/book/src/guides/adding_languages.md

Adding languages

Language configuration

To add a new language, you need to add a language entry to the languages.toml found in the root of the repository; this languages.toml file is included at compilation time, and is distinct from the languages.toml file in the user's configuration directory.

[[language]]
name = "mylang"
scope = "scope.mylang"
injection-regex = "^mylang$"
file-types = ["mylang", "myl"]
comment-token = "#"
indent = { tab-width = 2, unit = "  " }

These are the available keys and descriptions for the file.

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"]. Extensions and full file names are supported.
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
config	Language server configuration
grammar	The tree-sitter grammar to use (defaults to the value of name)

Grammar configuration

If a tree-sitter grammar is available for the language, add a new grammar entry to languages.toml.

[[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
path	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 --build-grammars to the correct path for compilation. When ommitted, the root of the grammar directory is used
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

Or a path key with an absolute path to a locally available grammar directory.

Queries

For a language to have syntax-highlighting and indentation among other things, you have to add queries. Add a directory for your language with the path runtime/queries/<name>/. The tree-sitter website gives more info on how to write queries.

NOTE: When evaluating queries, the first matching query takes precedence, which is different from other editors like neovim where the last matching query supersedes the ones before it. See this issue for an example.

Common Issues

• If you get errors when running after switching branches, you may have to update the tree-sitter grammars. Run hx --fetch-grammars to fetch the grammars and hx --build-grammars to build any out-of-date grammars.

• If a parser is segfaulting or you want to remove the parser, make sure to remove the compiled parser in runtime/grammar/<name>.so

• The indents query is indents.toml, not indents.scm. See this issue for more information.