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
157Zed uses these to highlight matching brackets: painting each bracket pair with a different color ("rainbow brackets") and highlighting the brackets if the cursor is inside the bracket pair.
158
159To opt out of rainbow brackets colorization, add the following to the corresponding `brackets.scm` entry:
160
161```scheme
162(("\"" @open "\"" @close) (#set! rainbow.exclude))
163```
164
165### Code outline/structure
166
167The `outline.scm` file defines the structure for the code outline.
168
169Here's an example from an `outline.scm` file for JSON:
170
171```scheme
172(pair
173 key: (string (string_content) @name)) @item
174```
175
176This query captures object keys for the outline structure.
177
178| Capture | Description |
179| -------------- | ------------------------------------------------------------------------------------ |
180| @name | Captures the content of object keys |
181| @item | Captures the entire key-value pair |
182| @context | Captures elements that provide context for the outline item |
183| @context.extra | Captures additional contextual information for the outline item |
184| @annotation | Captures nodes that annotate outline item (doc comments, attributes, decorators)[^1] |
185
186[^1]: These annotations are used by Assistant when generating code modification steps.
187
188### Auto-indentation
189
190The `indents.scm` file defines indentation rules.
191
192Here's an example from an `indents.scm` file for JSON:
193
194```scheme
195(array "]" @end) @indent
196(object "}" @end) @indent
197```
198
199This query marks the end of arrays and objects for indentation purposes.
200
201| Capture | Description |
202| ------- | -------------------------------------------------- |
203| @end | Captures closing brackets and braces |
204| @indent | Captures entire arrays and objects for indentation |
205
206### Code injections
207
208The `injections.scm` file defines rules for embedding one language within another, such as code blocks in Markdown or SQL queries in Python strings.
209
210Here's an example from an `injections.scm` file for Markdown:
211
212```scheme
213(fenced_code_block
214 (info_string
215 (language) @injection.language)
216 (code_fence_content) @injection.content)
217
218((inline) @content
219 (#set! injection.language "markdown-inline"))
220```
221
222This 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".
223
224| Capture | Description |
225| ------------------- | ---------------------------------------------------------- |
226| @injection.language | Captures the language identifier for a code block |
227| @injection.content | Captures the content to be treated as a different language |
228
229Note that we couldn't use JSON as an example here because it doesn't support language injections.
230
231### Syntax overrides
232
233The `overrides.scm` file defines syntactic _scopes_ that can be used to override certain editor settings within specific language constructs.
234
235For 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, "$" and "#" are considered word characters.
236
237There is also a language-specific setting called `completion_query_characters` that controls which characters trigger autocomplete suggestions. In JavaScript, when your cursor is within a _string_, "-" is should be considered a completion query character. To achieve this, the JavaScript `overrides.scm` file contains the following pattern:
238
239```scheme
240[
241 (string)
242 (template_string)
243] @string
244```
245
246And the JavaScript `config.toml` contains this setting:
247
248```toml
249word_characters = ["#", "$"]
250
251[overrides.string]
252completion_query_characters = ["-"]
253```
254
255You 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`:
256
257```toml
258brackets = [
259 { start = "'", end = "'", close = true, newline = false, not_in = ["string"] },
260 # other pairs...
261]
262```
263
264#### Range inclusivity
265
266By 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.
267
268For 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:
269
270```scheme
271(comment) @comment.inclusive
272```
273
274### Text objects
275
276The `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.
277
278Vim 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.
279
280For 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.
281
282For 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.
283
284If 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.
285
286| Capture | Description | Vim mode |
287| ---------------- | ----------------------------------------------------------------------- | ------------------------------------------------ |
288| @function.around | An entire function definition or equivalent small section of a file. | `[m`, `]m`, `[M`,`]M` motions. `af` text object |
289| @function.inside | The function body (the stuff within the braces). | `if` text object |
290| @class.around | An entire class definition or equivalent large section of a file. | `[[`, `]]`, `[]`, `][` motions. `ac` text object |
291| @class.inside | The contents of a class definition. | `ic` text object |
292| @comment.around | An entire comment (e.g. all adjacent line comments, or a block comment) | `gc` text object |
293| @comment.inside | The contents of a comment | `igc` text object (rarely supported) |
294
295For example:
296
297```scheme
298; include only the content of the method in the function
299(method_definition
300 body: (_
301 "{"
302 (_)* @function.inside
303 "}")) @function.around
304
305; match function.around for declarations with no body
306(function_signature_item) @function.around
307
308; join all adjacent comments into one
309(comment)+ @comment.around
310```
311
312### Text redactions
313
314The `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.
315
316Here's an example from a `redactions.scm` file for JSON:
317
318```scheme
319(pair value: (number) @redact)
320(pair value: (string) @redact)
321(array (number) @redact)
322(array (string) @redact)
323```
324
325This query marks number and string values in key-value pairs and arrays for redaction.
326
327| Capture | Description |
328| ------- | ------------------------------ |
329| @redact | Captures values to be redacted |
330
331### Runnable code detection
332
333The `runnables.scm` file defines rules for detecting runnable code.
334
335Here's an example from a `runnables.scm` file for JSON:
336
337```scheme
338(
339 (document
340 (object
341 (pair
342 key: (string
343 (string_content) @_name
344 (#eq? @_name "scripts")
345 )
346 value: (object
347 (pair
348 key: (string (string_content) @run @script)
349 )
350 )
351 )
352 )
353 )
354 (#set! tag package-script)
355 (#set! tag composer-script)
356)
357```
358
359This query detects runnable scripts in package.json and composer.json files.
360
361The `@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.
362
363| Capture | Description |
364| ------- | ------------------------------------------------------ |
365| @\_name | Captures the "scripts" key |
366| @run | Captures the script name |
367| @script | Also captures the script name (for different purposes) |
368
369<!--
370TBD: `#set! tag`
371-->
372
373## Language Servers
374
375Zed uses the [Language Server Protocol](https://microsoft.github.io/language-server-protocol/) to provide advanced language support.
376
377An 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:
378
379```toml
380[language_servers.my-language-server]
381name = "My Language LSP"
382languages = ["My Language"]
383```
384
385Then, in the Rust code for your extension, implement the `language_server_command` method on your extension:
386
387```rust
388impl zed::Extension for MyExtension {
389 fn language_server_command(
390 &mut self,
391 language_server_id: &LanguageServerId,
392 worktree: &zed::Worktree,
393 ) -> Result<zed::Command> {
394 Ok(zed::Command {
395 command: get_path_to_language_server_executable()?,
396 args: get_args_for_language_server()?,
397 env: get_env_for_language_server()?,
398 })
399 }
400}
401```
402
403You 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).
404
405### Multi-Language Support
406
407If 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:
408
409```toml
410
411[language-servers.my-language-server]
412name = "Whatever LSP"
413languages = ["JavaScript", "HTML", "CSS"]
414
415[language-servers.my-language-server.language_ids]
416"JavaScript" = "javascript"
417"TSX" = "typescriptreact"
418"HTML" = "html"
419"CSS" = "css"
420```