Language Extensions

Language support in Zed has several components:

• Language metadata and configuration
• Grammar
• Queries
• Language servers

Language Metadata

Each language supported by Zed must be defined in a subdirectory inside the languages directory of your extension.

This subdirectory must contain a file called config.toml file with the following structure:

name = "My Language"
grammar = "my-language"
path_suffixes = ["myl"]
line_comments = ["# "]

• name is the human readable name that will show up in the Select Language dropdown.
• grammar is the name of a grammar. Grammars are registered separately, described below.
• path_suffixes (optional) is an array of file suffixes that should be associated with this language. This supports glob patterns like config/**/*.toml where ** matches 0 or more directories and * matches 0 or more characters.
• line_comments (optional) is an array of strings that are used to identify line comments in the language.

Grammar

Zed uses the Tree-sitter parsing library to provide built-in language-specific features. There are grammars available for many languages, and you can also develop your own grammar. A growing list of Zed features are built using pattern matching over syntax trees with Tree-sitter queries. As mentioned above, every language that is defined in an extension must specify the name of a Tree-sitter grammar that is used for parsing. These grammars are then registered separately in extensions' extension.toml file, like this:

[grammars.gleam]
repository = "https://github.com/gleam-lang/tree-sitter-gleam"
commit = "58b7cac8fc14c92b0677c542610d8738c373fa81"

The repository field must specify a repository where the Tree-sitter grammar should be loaded from, and the commit field must contain the SHA of the Git commit to use. An extension can provide multiple grammars by referencing multiple tree-sitter repositories.

Tree-sitter Queries

Zed uses the syntax tree produced by the Tree-sitter query language to implement several features:

• Syntax highlighting
• Bracket matching
• Code outline/structure
• Auto-indentation
• Code injections
• Syntax overrides
• Text redactions
• Runnable code detection

The following sections elaborate on how Tree-sitter queries enable these features in Zed, using JSON syntax as a guiding example.

Syntax highlighting

In Tree-sitter, the highlights.scm file defines syntax highlighting rules for a particular syntax.

Here's an example from a highlights.scm for JSON:

(string) @string

(pair
  key: (string) @property.json_key)

(number) @number

This query marks strings, object keys, and numbers for highlighting. The following is a comprehensive list of captures supported by themes:

Bracket matching

The brackets.scm file defines matching brackets.

Here's an example from a brackets.scm file for JSON:

("[" @open "]" @close)
("{" @open "}" @close)
("\"" @open "\"" @close)

This query identifies opening and closing brackets, braces, and quotation marks.

Code outline/structure

The outline.scm file defines the structure for the code outline.

Here's an example from an outline.scm file for JSON:

(pair
  key: (string (string_content) @name)) @item

This query captures object keys for the outline structure.

[^1]: These annotations are used by Assistant when generating code modification steps.

Auto-indentation

The indents.scm file defines indentation rules.

Here's an example from an indents.scm file for JSON:

(array "]" @end) @indent
(object "}" @end) @indent

This query marks the end of arrays and objects for indentation purposes.

Code injections

The injections.scm file defines rules for embedding one language within another, such as code blocks in Markdown or SQL queries in Python strings.

Here's an example from an injections.scm file for Markdown:

(fenced_code_block
  (info_string
    (language) @language)
  (code_fence_content) @content)

((inline) @content
 (#set! "language" "markdown-inline"))

This query identifies fenced code blocks, capturing the language specified in the info string and the content within the block. It also captures inline content and sets its language to "markdown-inline".

Note that we couldn't use JSON as an example here because it doesn't support language injections.

Syntax overrides

The overrides.scm file defines syntax overrides.

Here's an example from an overrides.scm file for JSON:

(string) @string

This query explicitly marks strings for highlighting, potentially overriding default behavior. For a complete list of supported captures, refer to the Syntax highlighting section above.

Text redactions

The redactions.scm file defines text redaction rules. When collaborating and sharing your screen, it makes sure that certain syntax nodes are rendered in a redacted mode to avoid them from leaking.

Here's an example from a redactions.scm file for JSON:

(pair value: (number) @redact)
(pair value: (string) @redact)
(array (number) @redact)
(array (string) @redact)

This query marks number and string values in key-value pairs and arrays for redaction.

Runnable code detection

The runnables.scm file defines rules for detecting runnable code.

Here's an example from an runnables.scm file for JSON:

(
    (document
        (object
            (pair
                key: (string
                    (string_content) @_name
                    (#eq? @_name "scripts")
                )
                value: (object
                    (pair
                        key: (string (string_content) @run @script)
                    )
                )
            )
        )
    )
    (#set! tag package-script)
    (#set! tag composer-script)
)

This query detects runnable scripts in package.json and composer.json files.

The @run capture specifies where the run button should appear in the editor. Other captures, except those prefixed with an underscore, are exposed as environment variables with a prefix of ZED_CUSTOM_$(capture_name) when running the code.

Language Servers

Zed uses the Language Server Protocol to provide advanced language support.

An extension may provide any number of language servers. To provide a language server from your extension, add an entry to your extension.toml with the name of your language server and the language it applies to:

[language_servers.my-language]
name = "My Language LSP"
language = "My Language"

Then, in the Rust code for your extension, implement the language_server_command method on your extension:

impl zed::Extension for MyExtension {
    fn language_server_command(
        &mut self,
        language_server_id: &LanguageServerId,
        worktree: &zed::Worktree,
    ) -> Result<zed::Command> {
        Ok(zed::Command {
            command: get_path_to_language_server_executable()?,
            args: get_args_for_language_server()?,
            env: get_env_for_language_server()?,
        })
    }
}

You can customize the handling of the language server using several optional methods in the Extension trait. For example, you can control how completions are styled using the label_for_completion method. For a complete list of methods, see the API docs for the Zed extension API.