1# Language Extensions
2
3Language support in Zed has several components:
4
5- Language metadata and configuration
6- Grammar
7- Queries
8- Language servers
9
10## Language Metadata
11
12Each language supported by Zed must be defined in a subdirectory inside the `languages` directory of your extension.
13
14This subdirectory must contain a file called `config.toml` file with the following structure:
15
16```toml
17name = "My Language"
18grammar = "my-language"
19path_suffixes = ["myl"]
20line_comments = ["# "]
21```
22
23- `name` (required) is the human readable name that will show up in the Select Language dropdown.
24- `grammar` (required) is the name of a grammar. Grammars are registered separately, described below.
25- `path_suffixes` is an array of file suffixes that should be associated with this language. Unlike `file_types` in settings, this does not support glob patterns.
26- `line_comments` is an array of strings that are used to identify line comments in the language. This is used for the `editor::ToggleComments` keybind: {#kb editor::ToggleComments} for toggling lines of code.
27- `tab_size` defines the indentation/tab size used for this language (default is `4`).
28- `hard_tabs` whether to indent with tabs (`true`) or spaces (`false`, the default).
29- `first_line_pattern` is a regular expression, that in addition to `path_suffixes` (above) or `file_types` in settings can be used to match files which should use this language. For example Zed uses this to identify Shell Scripts by matching the [shebangs lines](https://github.com/zed-industries/zed/blob/main/crates/languages/src/bash/config.toml) in the first line of a script.
30- `debuggers` is an array of strings that are used to identify debuggers in the language. When launching a debugger's `New Process Modal`, Zed will order available debuggers by the order of entries in this array.
31
32<!--
33TBD: Document `language_name/config.toml` keys
34
35- autoclose_before
36- brackets (start, end, close, newline, not_in: ["comment", "string"])
37- word_characters
38- prettier_parser_name
39- opt_into_language_servers
40- code_fence_block_name
41- scope_opt_in_language_servers
42- increase_indent_pattern, decrease_indent_pattern
43- collapsed_placeholder
44- auto_indent_on_paste, auto_indent_using_last_non_empty_line
45- overrides: `[overrides.element]`, `[overrides.string]`
46-->
47
48## Grammar
49
50Zed uses the [Tree-sitter](https://tree-sitter.github.io) parsing library to provide built-in language-specific features. There are grammars available for many languages, and you can also [develop your own grammar](https://tree-sitter.github.io/tree-sitter/creating-parsers#writing-the-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:
51
52```toml
53[grammars.gleam]
54repository = "https://github.com/gleam-lang/tree-sitter-gleam"
55rev = "58b7cac8fc14c92b0677c542610d8738c373fa81"
56```
57
58The `repository` field must specify a repository where the Tree-sitter grammar should be loaded from, and the `rev` field must contain a Git revision to use, such as the SHA of a Git commit. If you're developing an extension locally and want to load a grammar from the local filesystem, you can use a `file://` URL for `repository`. An extension can provide multiple grammars by referencing multiple tree-sitter repositories.
59
60## Tree-sitter Queries
61
62Zed uses the syntax tree produced by the [Tree-sitter](https://tree-sitter.github.io) query language to implement
63several features:
64
65- Syntax highlighting
66- Bracket matching
67- Code outline/structure
68- Auto-indentation
69- Code injections
70- Syntax overrides
71- Text redactions
72- Runnable code detection
73- Selecting classes, functions, etc.
74
75The following sections elaborate on how [Tree-sitter queries](https://tree-sitter.github.io/tree-sitter/using-parsers#query-syntax) enable these
76features in Zed, using [JSON syntax](https://www.json.org/json-en.html) as a guiding example.
77
78### Syntax highlighting
79
80In Tree-sitter, the `highlights.scm` file defines syntax highlighting rules for a particular syntax.
81
82Here's an example from a `highlights.scm` for JSON:
83
84```scheme
85(string) @string
86
87(pair
88 key: (string) @property.json_key)
89
90(number) @number
91```
92
93This query marks strings, object keys, and numbers for highlighting. The following is a comprehensive list of captures supported by themes:
94
95| Capture | Description |
96| ------------------------ | -------------------------------------- |
97| @attribute | Captures attributes |
98| @boolean | Captures boolean values |
99| @comment | Captures comments |
100| @comment.doc | Captures documentation comments |
101| @constant | Captures constants |
102| @constructor | Captures constructors |
103| @embedded | Captures embedded content |
104| @emphasis | Captures emphasized text |
105| @emphasis.strong | Captures strongly emphasized text |
106| @enum | Captures enumerations |
107| @function | Captures functions |
108| @hint | Captures hints |
109| @keyword | Captures keywords |
110| @label | Captures labels |
111| @link_text | Captures link text |
112| @link_uri | Captures link URIs |
113| @number | Captures numeric values |
114| @operator | Captures operators |
115| @predictive | Captures predictive text |
116| @preproc | Captures preprocessor directives |
117| @primary | Captures primary elements |
118| @property | Captures properties |
119| @punctuation | Captures punctuation |
120| @punctuation.bracket | Captures brackets |
121| @punctuation.delimiter | Captures delimiters |
122| @punctuation.list_marker | Captures list markers |
123| @punctuation.special | Captures special punctuation |
124| @string | Captures string literals |
125| @string.escape | Captures escaped characters in strings |
126| @string.regex | Captures regular expressions |
127| @string.special | Captures special strings |
128| @string.special.symbol | Captures special symbols |
129| @tag | Captures tags |
130| @tag.doctype | Captures doctypes (e.g., in HTML) |
131| @text.literal | Captures literal text |
132| @title | Captures titles |
133| @type | Captures types |
134| @variable | Captures variables |
135| @variable.special | Captures special variables |
136| @variant | Captures variants |
137
138### Bracket matching
139
140The `brackets.scm` file defines matching brackets.
141
142Here's an example from a `brackets.scm` file for JSON:
143
144```scheme
145("[" @open "]" @close)
146("{" @open "}" @close)
147("\"" @open "\"" @close)
148```
149
150This query identifies opening and closing brackets, braces, and quotation marks.
151
152| Capture | Description |
153| ------- | --------------------------------------------- |
154| @open | Captures opening brackets, braces, and quotes |
155| @close | Captures closing brackets, braces, and quotes |
156
157### Code outline/structure
158
159The `outline.scm` file defines the structure for the code outline.
160
161Here's an example from an `outline.scm` file for JSON:
162
163```scheme
164(pair
165 key: (string (string_content) @name)) @item
166```
167
168This query captures object keys for the outline structure.
169
170| Capture | Description |
171| -------------- | ------------------------------------------------------------------------------------ |
172| @name | Captures the content of object keys |
173| @item | Captures the entire key-value pair |
174| @context | Captures elements that provide context for the outline item |
175| @context.extra | Captures additional contextual information for the outline item |
176| @annotation | Captures nodes that annotate outline item (doc comments, attributes, decorators)[^1] |
177
178[^1]: These annotations are used by Assistant when generating code modification steps.
179
180### Auto-indentation
181
182The `indents.scm` file defines indentation rules.
183
184Here's an example from an `indents.scm` file for JSON:
185
186```scheme
187(array "]" @end) @indent
188(object "}" @end) @indent
189```
190
191This query marks the end of arrays and objects for indentation purposes.
192
193| Capture | Description |
194| ------- | -------------------------------------------------- |
195| @end | Captures closing brackets and braces |
196| @indent | Captures entire arrays and objects for indentation |
197
198### Code injections
199
200The `injections.scm` file defines rules for embedding one language within another, such as code blocks in Markdown or SQL queries in Python strings.
201
202Here's an example from an `injections.scm` file for Markdown:
203
204```scheme
205(fenced_code_block
206 (info_string
207 (language) @injection.language)
208 (code_fence_content) @injection.content)
209
210((inline) @content
211 (#set! injection.language "markdown-inline"))
212```
213
214This 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".
215
216| Capture | Description |
217| ------------------- | ---------------------------------------------------------- |
218| @injection.language | Captures the language identifier for a code block |
219| @injection.content | Captures the content to be treated as a different language |
220
221Note that we couldn't use JSON as an example here because it doesn't support language injections.
222
223### Syntax overrides
224
225The `overrides.scm` file defines syntactic _scopes_ that can be used to override certain editor settings within specific language constructs.
226
227For example, there is a language-specific setting called `word_characters` that controls which non-alphabetic characters are considered part of a word, for example when you double click to select a variable. In JavaScript, "$" and "#" are considered word characters.
228
229There is also a language-specific setting called `completion_query_characters` that controls which characters trigger autocomplete suggestions. In JavaScript, when your cursor is within a _string_, "-" is should be considered a completion query character. To achieve this, the JavaScript `overrides.scm` file contains the following pattern:
230
231```scheme
232[
233 (string)
234 (template_string)
235] @string
236```
237
238And the JavaScript `config.toml` contains this setting:
239
240```toml
241word_characters = ["#", "$"]
242
243[overrides.string]
244completion_query_characters = ["-"]
245```
246
247You can also disable certain auto-closing brackets in a specific scope. For example, to prevent auto-closing `'` within strings, you could put the following in the JavaScript `config.toml`:
248
249```toml
250brackets = [
251 { start = "'", end = "'", close = true, newline = false, not_in = ["string"] },
252 # other pairs...
253]
254```
255
256#### Range inclusivity
257
258By default, the ranges defined in `overrides.scm` are _exclusive_. So in the case above, if you cursor was _outside_ the quotation marks delimiting the string, the `string` scope would not take effect. Sometimes, you may want to make the range _inclusive_. You can do this by adding the `.inclusive` suffix to the capture name in the query.
259
260For example, in JavaScript, we also disable auto-closing of single quotes within comments. And the comment scope must extend all the way to the newline after a line comment. To achieve this, the JavaScript `overrides.scm` contains the following pattern:
261
262```scheme
263(comment) @comment.inclusive
264```
265
266### Text objects
267
268The `textobjects.scm` file defines rules for navigating by text objects. This was added in Zed v0.165 and is currently used only in Vim mode.
269
270Vim provides two levels of granularity for navigating around files. Section-by-section with `[]` etc., and method-by-method with `]m` etc. Even languages that don't support functions and classes can work well by defining similar concepts. For example CSS defines a rule-set as a method, and a media-query as a class.
271
272For languages with closures, these typically should not count as functions in Zed. This is best-effort however, as languages like JavaScript do not syntactically differentiate syntactically between closures and top-level function declarations.
273
274For languages with declarations like C, provide queries that match `@class.around` or `@function.around`. The `if` and `ic` text objects will default to these if there is no inside.
275
276If you are not sure what to put in textobjects.scm, both [nvim-treesitter-textobjects](https://github.com/nvim-treesitter/nvim-treesitter-textobjects), and the [Helix editor](https://github.com/helix-editor/helix) have queries for many languages. You can refer to the Zed [built-in languages](https://github.com/zed-industries/zed/tree/main/crates/languages/src) to see how to adapt these.
277
278| Capture | Description | Vim mode |
279| ---------------- | ----------------------------------------------------------------------- | ------------------------------------------------ |
280| @function.around | An entire function definition or equivalent small section of a file. | `[m`, `]m`, `[M`,`]M` motions. `af` text object |
281| @function.inside | The function body (the stuff within the braces). | `if` text object |
282| @class.around | An entire class definition or equivalent large section of a file. | `[[`, `]]`, `[]`, `][` motions. `ac` text object |
283| @class.inside | The contents of a class definition. | `ic` text object |
284| @comment.around | An entire comment (e.g. all adjacent line comments, or a block comment) | `gc` text object |
285| @comment.inside | The contents of a comment | `igc` text object (rarely supported) |
286
287For example:
288
289```scheme
290; include only the content of the method in the function
291(method_definition
292 body: (_
293 "{"
294 (_)* @function.inside
295 "}")) @function.around
296
297; match function.around for declarations with no body
298(function_signature_item) @function.around
299
300; join all adjacent comments into one
301(comment)+ @comment.around
302```
303
304### Text redactions
305
306The `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.
307
308Here's an example from a `redactions.scm` file for JSON:
309
310```scheme
311(pair value: (number) @redact)
312(pair value: (string) @redact)
313(array (number) @redact)
314(array (string) @redact)
315```
316
317This query marks number and string values in key-value pairs and arrays for redaction.
318
319| Capture | Description |
320| ------- | ------------------------------ |
321| @redact | Captures values to be redacted |
322
323### Runnable code detection
324
325The `runnables.scm` file defines rules for detecting runnable code.
326
327Here's an example from a `runnables.scm` file for JSON:
328
329```scheme
330(
331 (document
332 (object
333 (pair
334 key: (string
335 (string_content) @_name
336 (#eq? @_name "scripts")
337 )
338 value: (object
339 (pair
340 key: (string (string_content) @run @script)
341 )
342 )
343 )
344 )
345 )
346 (#set! tag package-script)
347 (#set! tag composer-script)
348)
349```
350
351This query detects runnable scripts in package.json and composer.json files.
352
353The `@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.
354
355| Capture | Description |
356| ------- | ------------------------------------------------------ |
357| @\_name | Captures the "scripts" key |
358| @run | Captures the script name |
359| @script | Also captures the script name (for different purposes) |
360
361<!--
362TBD: `#set! tag`
363-->
364
365## Language Servers
366
367Zed uses the [Language Server Protocol](https://microsoft.github.io/language-server-protocol/) to provide advanced language support.
368
369An 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(s) it applies to. The entry in the list of `languages` has to match the `name` field from the `config.toml` file for that language:
370
371```toml
372[language_servers.my-language-server]
373name = "My Language LSP"
374languages = ["My Language"]
375```
376
377Then, in the Rust code for your extension, implement the `language_server_command` method on your extension:
378
379```rust
380impl zed::Extension for MyExtension {
381 fn language_server_command(
382 &mut self,
383 language_server_id: &LanguageServerId,
384 worktree: &zed::Worktree,
385 ) -> Result<zed::Command> {
386 Ok(zed::Command {
387 command: get_path_to_language_server_executable()?,
388 args: get_args_for_language_server()?,
389 env: get_env_for_language_server()?,
390 })
391 }
392}
393```
394
395You 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](https://docs.rs/zed_extension_api).
396
397### Multi-Language Support
398
399If your language server supports additional languages, you can use `language_ids` to map Zed `languages` to the desired [LSP-specific `languageId`](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocumentItem) identifiers:
400
401```toml
402
403[language-servers.my-language-server]
404name = "Whatever LSP"
405languages = ["JavaScript", "HTML", "CSS"]
406
407[language-servers.my-language-server.language_ids]
408"JavaScript" = "javascript"
409"TSX" = "typescriptreact"
410"HTML" = "html"
411"CSS" = "css"
412```