WebAssembly API Reference

WebAssembly API Reference v1.15.7

Functions

detectLanguageFromExtension()

Detect language name from a file extension (without leading dot).

Returns null for unrecognized extensions. The match is case-insensitive.

Signature:

function detectLanguageFromExtension(ext: string): string | null

Example:

const result = detectLanguageFromExtension("value");

Parameters:

Name	Type	Required	Description
ext	string	Yes	The ext

Returns: string | null

---

detectLanguageFromPath()

Detect language name from a file path.

Extracts the file extension and looks it up. Returns null if the path has no extension or the extension is not recognized.

Signature:

function detectLanguageFromPath(path: string): string | null

Example:

const result = detectLanguageFromPath("value");

Parameters:

Name	Type	Required	Description
path	string	Yes	Path to the file

Returns: string | null

---

detectLanguageFromContent()

Detect language name from file content using the shebang line (#!).

Inspects only the first line of content. If it begins with #!, the interpreter name is extracted and mapped to a language name.

Handles common patterns:

• #!/usr/bin/env python3 → "python"
• #!/bin/bash → "bash"
• #!/usr/bin/env node → "javascript"

The -S flag accepted by some env implementations is skipped automatically. Version suffixes (e.g. python3.11, ruby3.2) are stripped before matching.

A leading UTF-8 BOM (U+FEFF) is skipped before the #! check, so a BOM-prefixed script is still detected by its shebang.

Returns null when content does not start with #! (after stripping a leading BOM), the shebang is malformed, or the interpreter is not recognised.

Signature:

function detectLanguageFromContent(content: string): string | null

Example:

const result = detectLanguageFromContent("value");

Parameters:

Name	Type	Required	Description
content	string	Yes	The content to process

Returns: string | null

---

getHighlightsQuery()

Get the highlights query for a language, if bundled.

Returns the contents of highlights.scm as a static string, or null if no highlights query is bundled for this language.

Signature:

function getHighlightsQuery(language: string): string | null

Example:

const result = getHighlightsQuery("value");

Parameters:

Name	Type	Required	Description
language	string	Yes	The language

Returns: string | null

---

getInjectionsQuery()

Get the injections query for a language, if bundled.

Returns the contents of injections.scm as a static string, or null if no injections query is bundled for this language.

Signature:

function getInjectionsQuery(language: string): string | null

Example:

const result = getInjectionsQuery("value");

Parameters:

Name	Type	Required	Description
language	string	Yes	The language

Returns: string | null

---

getLocalsQuery()

Get the locals query for a language, if bundled.

Returns the contents of locals.scm as a static string, or null if no locals query is bundled for this language.

Signature:

function getLocalsQuery(language: string): string | null

Example:

const result = getLocalsQuery("value");

Parameters:

Name	Type	Required	Description
language	string	Yes	The language

Returns: string | null

---

getTagsQuery()

Get the tags query for a language, if bundled.

Returns the contents of tags.scm as a static string, or null if no tags query is bundled for this language.

Signature:

function getTagsQuery(language: string): string | null

Example:

const result = getTagsQuery("value");

Parameters:

Name	Type	Required	Description
language	string	Yes	The language

Returns: string | null

---

getIndentsQuery()

Get the indents query for a language, if bundled.

Returns the contents of indents.scm (used for auto-indentation) as a static string, or null if no indents query is bundled for this language.

Signature:

function getIndentsQuery(language: string): string | null

Example:

const result = getIndentsQuery("value");

Parameters:

Name	Type	Required	Description
language	string	Yes	The language

Returns: string | null

---

getFoldsQuery()

Get the folds query for a language, if bundled.

Returns the contents of folds.scm (used for code folding) as a static string, or null if no folds query is bundled for this language.

Signature:

function getFoldsQuery(language: string): string | null

Example:

const result = getFoldsQuery("value");

Parameters:

Name	Type	Required	Description
language	string	Yes	The language

Returns: string | null

---

getLanguage()

Get a tree-sitter Language by name using the global registry.

Resolves language aliases (e.g., "shell" maps to "bash"). When the download feature is enabled (default), automatically downloads the parser from GitHub releases if not found locally.

Errors:

Returns Error.LanguageNotFound if the language is not recognized, or Error.Download if auto-download fails.

Signature:

function getLanguage(name: string): Language

Example:

const result = getLanguage("value");

Parameters:

Name	Type	Required	Description
name	string	Yes	The name

Returns: Language

Errors: Throws Error with a descriptive message.

---

getParser()

Get a Parser pre-configured for the given language.

This is a convenience function that calls get_language and configures a new parser in one step.

Errors:

Returns Error.LanguageNotFound if the language is not recognized, or Error.ParserSetup if the language cannot be applied to the parser.

Signature:

function getParser(name: string): Parser

Example:

const result = getParser("value");

Parameters:

Name	Type	Required	Description
name	string	Yes	The name

Returns: Parser

Errors: Throws Error with a descriptive message.

---

detectLanguage()

Detect language name from a file path or extension.

This compatibility alias matches the pre-Alef Python binding API.

Signature:

function detectLanguage(path: string): string | null

Example:

const result = detectLanguage("value");

Parameters:

Name	Type	Required	Description
path	string	Yes	Path to the file

Returns: string | null

---

availableLanguages()

List all available language names (sorted, deduplicated, includes aliases).

Returns names of both statically compiled and dynamically loadable languages, plus any configured aliases.

Signature:

function availableLanguages(): Array<string>

Example:

const result = availableLanguages();

Returns: Array<string>

---

hasLanguage()

Check if a language is available by name or alias.

Returns true if the language can be loaded (statically compiled, dynamically available, or a known alias for one of these).

Signature:

function hasLanguage(name: string): boolean

Example:

const result = hasLanguage("value");

Parameters:

Name	Type	Required	Description
name	string	Yes	The name

Returns: boolean

---

languageCount()

Return the number of available languages.

Includes statically compiled languages, dynamically loadable languages, and aliases.

Signature:

function languageCount(): number

Example:

const result = languageCount();

Returns: number

---

process()

Process source code and extract file intelligence using the global registry.

Parses the source with tree-sitter and extracts metrics, structure, imports, exports, comments, docstrings, symbols, diagnostics, and/or chunks based on the flags set in ProcessConfig.

Errors:

Returns Error.InvalidRange if the config carries a zero-valued limit or the source exceeds ProcessConfig.max_source_bytes, Error.ParseTimeout if the parse exceeds ProcessConfig.parse_timeout_ms, Error.LanguageNotFound if the language is unknown, or Error.ParseFailed if parsing yields no tree.

Signature:

function process(source: string, config: ProcessConfig): ProcessResult

Example:

const result = process("value", new ProcessConfig());

Parameters:

Name	Type	Required	Description
source	string	Yes	The source
config	ProcessConfig	Yes	The configuration options

Returns: ProcessResult

Errors: Throws Error with a descriptive message.

---

prefetch()

Prefetch grammars by loading each into the registry.

Without the download feature there is no network step — every requested language must already be statically compiled or present on disk.

Errors:

Returns Error.LanguageNotFound if a requested language is not available.

Signature:

function prefetch(languages: Array<string>): void

Example:

prefetch([]);

Parameters:

Name	Type	Required	Description
languages	Array<string>	Yes	The languages

Returns: No return value.

Errors: Throws Error with a descriptive message.

---

Types

ByteRange

A byte range — start (inclusive) to end (exclusive).

Field	Type	Default	Description
start	number	—	Inclusive start byte offset.
end	number	—	Exclusive end byte offset.

---

ChunkContext

Metadata for a single chunk of source code.

Field	Type	Default	Description
language	string	—	Language name used to parse this chunk.
chunkIndex	number	—	Zero-indexed position of this chunk within the file’s chunk list.
totalChunks	number	—	Total number of chunks the file was split into.
nodeTypes	Array<string>	[]	Tree-sitter node kinds that appear at the top level of this chunk.
contextPath	Array<string>	[]	Hierarchical path of enclosing structural items (e.g., ["MyClass", "my_method"]).
symbolsDefined	Array<string>	[]	Names of symbols defined within this chunk.
comments	Array<CommentInfo>	[]	Comments contained within this chunk.
docstrings	Array<DocstringInfo>	[]	Docstrings contained within this chunk. Populated only for Python — the same language for which ProcessResult.docstrings is populated, and by the same classifier. Always empty for every other language.
hasErrorNodes	boolean	—	Whether this chunk contains any tree-sitter error nodes.

---

CodeChunk

A chunk of source code with rich metadata.

Field	Type	Default	Description
content	string	—	The raw source text of this chunk.
startByte	number	—	Inclusive start byte offset of this chunk in the original source.
endByte	number	—	Exclusive end byte offset of this chunk in the original source.
startLine	number	—	Zero-indexed start line of this chunk.
endLine	number	—	Zero-indexed row of the last byte actually included in this chunk (inclusive — the same row a Span.end_line would report for a node ending on that byte). Computed the same way regardless of whether the source has a trailing newline: it is always the row of end_byte - 1, never a phantom row past the file’s real content.
metadata	ChunkContext	—	Contextual metadata about this chunk.

---

CommentInfo

A comment extracted from source code.

Field	Type	Default	Description
text	string	—	The raw text content of the comment.
kind	CommentKind	CommentKind.Line	The kind of comment (line, block, or doc).
span	Span	—	Source span covering the comment.
associatedNode	string | null	null	Name of the syntax node this comment is directly associated with.

---

DataAttribute

An XML-style attribute attached to an Element node.

Populated only for DataNodeKind.Element; always empty for KeyValue and Sequence nodes.

Field	Type	Default	Description
name	string	—	Attribute name (e.g. "class", "href").
value	string	—	Attribute value as a raw string (quotes stripped).
span	Span	—	Source span covering the entire name="value" attribute token.

---

DataNode

A node in the hierarchical data tree produced by data-format extraction.

When ProcessConfig.data_extraction is true, ProcessResult.data is populated with a root DataNode whose children mirror the structure of the parsed file.

The kind field determines which other fields are meaningful:

kind	key	value	attributes	children
KeyValue	key / mapping key / index	leaf value	empty	nested map
Element	XML tag name	text content	XML attrs	child elements
Sequence	positional index ("0")	leaf value	empty	sub-items

Field	Type	Default	Description
kind	DataNodeKind	DataNodeKind.KeyValue	Whether this node is a key/value pair, XML element, or sequence item.
key	string | null	null	Key, attribute name, tag name, or positional index ("0", "1", …). null at the document root.
value	string | null	null	Leaf scalar value, if any. null for containers (objects, arrays, XML elements with child elements).
attributes	Array<DataAttribute>	[]	Attributes on element-shape nodes (XML STag attributes). Empty for all other kinds.
children	Array<DataNode>	[]	Children for nested containers and XML element bodies.
span	Span	—	Source span covering this node in the original source file.

---

Diagnostic

A diagnostic (syntax error, missing node, etc.) from parsing.

Field	Type	Default	Description
message	string	—	Human-readable description of the diagnostic.
severity	DiagnosticSeverity	DiagnosticSeverity.Error	Severity of the diagnostic.
span	Span	—	Source span where the diagnostic was detected.

---

DocSection

A section within a docstring (e.g., Args, Returns, Raises).

Field	Type	Default	Description
kind	string	—	Section kind (e.g., "args", "returns", "raises").
name	string | null	null	Parameter or return value name, if applicable.
description	string	—	Description text for this section.

---

DocstringInfo

A docstring extracted from source code.

Field	Type	Default	Description
text	string	—	The raw text of the docstring.
format	DocstringFormat	DocstringFormat.PythonTripleQuote	The docstring format (Python, JSDoc, Rustdoc, etc.).
span	Span	—	Source span covering the docstring.
associatedItem	string | null	null	Name of the item this docstring documents.
parsedSections	Array<DocSection>	[]	Parsed sections of the docstring (Args, Returns, Raises, etc.). Reserved: not yet populated. Always empty, for every DocstringFormat. Parsing a docstring body into sections requires implementing each convention’s own layout (Google/NumPy/reST style for Python, @param/@returns for JSDoc/Javadoc, and so on), which no extractor here does yet. The field is kept rather than removed so a consumer’s deserializer does not need updating once it is.

---

ExportInfo

An export statement extracted from source code.

Field	Type	Default	Description
name	string	—	The exported name.
kind	ExportKind	ExportKind.Named	The kind of export (named, default, or re-export).
span	Span	—	Source span covering the export statement.

---

FileMetrics

Aggregate metrics for a source file.

Field	Type	Default	Description
totalLines	number	—	Total number of lines (including blank and comment lines).
codeLines	number	—	Number of lines containing non-blank, non-comment source code.
commentLines	number	—	Number of lines that are entirely comments.
blankLines	number	—	Number of blank (whitespace-only) lines.
totalBytes	number	—	Total byte length of the source file.
nodeCount	number	—	Total number of nodes in the syntax tree.
errorCount	number	—	Number of error nodes in the syntax tree (parse errors).
maxDepth	number	—	Maximum nesting depth reached in the syntax tree.

---

ImportInfo

An import statement extracted from source code.

Field	Type	Default	Description
source	string	—	The module or path being imported from.
items	Array<string>	[]	Specific names imported from the source module. For import a, b / from m import a, b, every entry’s base name (never the alias). For a JavaScript/TypeScript named-imports clause (import { a, b as c } from 'm'), every specifier’s original name. Populated for Python and JavaScript/TypeScript only. Always empty for every other language this library recognises import statements for — Rust, Go, Java, Kotlin, and Elixir (import/alias/require/use) — and for a JS/TS namespace import (import * as ns) or default import (import x from 'm'), neither of which names individual items.
alias	string | null	null	Alias assigned to the import (e.g., import numpy as np). Populated for Python’s single-name form (import numpy as np, from m import a as b) and JavaScript/TypeScript’s namespace form (import * as ns from 'm') or a named-imports clause naming exactly one specifier (import { a as b } from 'm'). null for Rust, Go, Java, Kotlin, and Elixir (which has its own as: alias option on alias directives, not yet extracted here) — and for a Python statement that aliases several names at once (import os, sys as s), where there is no single alias to report for the statement as a whole, so only items is populated for it.
isWildcard	boolean	—	Whether this is a wildcard import (e.g., import * or use foo.*). Detected from the syntax tree — a dedicated wildcard node (wildcard_import in Python, use_wildcard in Rust) or a bare * token outside of string-literal content — not by searching the import’s source text for a * character, so a glob in an import path string (import a from './glob*.js') is not mistaken for one.
span	Span	—	Source span covering the import statement.

---

Language

---

LanguageRegistry

Thread-safe registry of tree-sitter language parsers.

Manages both statically compiled and dynamically loaded language grammars. Use LanguageRegistry.new() for the default registry, or access the global instance via the module-level convenience functions (get_language, available_languages, etc.).

Methods

new()

Create a new registry populated with all statically compiled languages.

When the dynamic-loading feature is enabled, the registry also knows about dynamically loadable grammars and will load them on demand.

Signature:

static new(): LanguageRegistry

Example:

const result = LanguageRegistry.new();

Returns: LanguageRegistry

getLanguage()

Get a tree-sitter Language by name.

Resolves aliases (e.g., "shell" -> "bash", "makefile" -> "make"), then looks up the language in the static table. When the dynamic-loading feature is enabled, falls back to loading a shared library on demand.

Errors:

Returns Error.LanguageNotFound if the name (after alias resolution) does not match any known grammar.

Signature:

getLanguage(name: string): Language

Example:

const result = instance.getLanguage("value");

Parameters:

Name	Type	Required	Description
name	string	Yes	The name

Returns: Language

Errors: Throws Error with a descriptive message.

availableLanguages()

List all available language names, sorted and deduplicated.

Includes statically compiled languages, dynamically loadable languages (if the dynamic-loading feature is enabled), and all configured aliases.

Signature:

availableLanguages(): Array<string>

Example:

const result = instance.availableLanguages();

Returns: Array<string>

hasParser()

Check whether this language can be parsed right now, without downloading.

Resolves aliases, then answers from exactly the lookup get_language performs: the statically compiled table, the already-loaded dynamic grammars, and the parser shared libraries present in the primary and extra (download-cache) library directories. It never performs network I/O.

A previous implementation consulted only the statically compiled table. That table is empty in every build that does not set TSLP_LANGUAGES, so the function answered false for languages this registry parses perfectly well.

Contrast has_language, which is also true for a grammar that is merely known to the manifest and would have to be downloaded first. The pair distinguishes “we can parse it offline, now” from “we recognise the name”.

The first true answer for a dynamic grammar loads its shared library: loading is the only way to know the grammar is usable, since a truncated or wrong-architecture library exists on disk but cannot parse. Loads are cached process-wide, so repeat calls are cheap.

use tree_sitter_language_pack::{detect_language_from_extension, LanguageRegistry};

let registry = LanguageRegistry::new();
// Extension detection uses the static ext table for all 371 grammars.
let lang = detect_language_from_extension("feature"); // always returns Some("gherkin")
// Parser availability depends on what is compiled in or cached on disk.
let can_parse = lang.map(|name| registry.has_parser(name)).unwrap_or(false);

Signature:

hasParser(name: string): boolean

Example:

const result = instance.hasParser("value");

Parameters:

Name	Type	Required	Description
name	string	Yes	The name

Returns: boolean

hasLanguage()

Check whether a language is available by name or alias.

Returns true if the language can be loaded, either from the static table or from a dynamic library on disk.

Every branch is one more way to answer true, so they are ordered cheapest-first and the filesystem is only consulted once every in-memory source has said no. Probing the loaded-grammar map and the manifest ahead of the stat calls is what keeps this off the syscall path for the languages a process actually uses.

Signature:

hasLanguage(name: string): boolean

Example:

const result = instance.hasLanguage("value");

Parameters:

Name	Type	Required	Description
name	string	Yes	The name

Returns: boolean

languageCount()

Return the total number of available languages (including aliases).

Counts the same set available_languages lists, without materialising or sorting it.

Signature:

languageCount(): number

Example:

const result = instance.languageCount();

Returns: number

process()

Parse source code and extract file intelligence based on config in a single pass.

Errors:

Returns Error.InvalidRange if the config is invalid (see ProcessConfig.validate) or if the source exceeds the configured max_source_bytes; Error.LanguageNotFound if the language is unknown; or Error.ParseFailed if parsing produces no tree.

Signature:

process(source: string, config: ProcessConfig): ProcessResult

Example:

const result = instance.process("value", new ProcessConfig());

Parameters:

Name	Type	Required	Description
source	string	Yes	The source
config	ProcessConfig	Yes	The configuration options

Returns: ProcessResult

Errors: Throws Error with a descriptive message.

---

Node

A single syntax node within a Tree.

Nodes hold a strong reference to their parent tree so they remain valid regardless of how the tree is moved or stored at the FFI boundary.

Methods

kind()

Return the node’s kind name (e.g. "function_definition").

Signature:

kind(): string

Example:

const result = instance.kind();

Returns: string

kindId()

Return the node’s numeric kind ID.

Tree-sitter assigns a stable u16 ID to every node kind in a grammar (e.g. "function_definition" → 42). Comparing kind_id() is cheaper than comparing the string kind() in tight AST loops.

Signature:

kindId(): number

Example:

const result = instance.kindId();

Returns: number

startByte()

Return the inclusive start byte offset of this node.

Signature:

startByte(): number

Example:

const result = instance.startByte();

Returns: number

endByte()

Return the exclusive end byte offset of this node.

Signature:

endByte(): number

Example:

const result = instance.endByte();

Returns: number

byteRange()

Return the node’s byte range as a ByteRange.

Callers should slice their own source bytes — this is a zero-copy text accessor.

Signature:

byteRange(): ByteRange

Example:

const result = instance.byteRange();

Returns: ByteRange

startPosition()

Return the start Point (row, column).

Signature:

startPosition(): Point

Example:

const result = instance.startPosition();

Returns: Point

endPosition()

Return the end Point (row, column).

Signature:

endPosition(): Point

Example:

const result = instance.endPosition();

Returns: Point

isNamed()

True when this node is named (not punctuation/whitespace).

Signature:

isNamed(): boolean

Example:

const result = instance.isNamed();

Returns: boolean

isError()

True when this is an error node.

Signature:

isError(): boolean

Example:

const result = instance.isError();

Returns: boolean

isMissing()

True when this is a missing-token node.

Signature:

isMissing(): boolean

Example:

const result = instance.isMissing();

Returns: boolean

isExtra()

True when this is an “extra” node (e.g. a comment).

Signature:

isExtra(): boolean

Example:

const result = instance.isExtra();

Returns: boolean

hasError()

True when this node or any descendant is an error.

Signature:

hasError(): boolean

Example:

const result = instance.hasError();

Returns: boolean

parent()

Return this node’s parent, if any.

Signature:

parent(): Node | null

Example:

const result = instance.parent();

Returns: Node | null

child()

Return the i-th child of this node, if any.

Signature:

child(index: number): Node | null

Example:

const result = instance.child(42);

Parameters:

Name	Type	Required	Description
index	number	Yes	The index

Returns: Node | null

childCount()

Total number of children (including unnamed).

Signature:

childCount(): number

Example:

const result = instance.childCount();

Returns: number

namedChild()

Return the i-th named child of this node, if any.

Signature:

namedChild(index: number): Node | null

Example:

const result = instance.namedChild(42);

Parameters:

Name	Type	Required	Description
index	number	Yes	The index

Returns: Node | null

namedChildCount()

Number of named children of this node.

Signature:

namedChildCount(): number

Example:

const result = instance.namedChildCount();

Returns: number

childByFieldName()

Look up a child by its grammar-defined field name.

Signature:

childByFieldName(name: string): Node | null

Example:

const result = instance.childByFieldName("value");

Parameters:

Name	Type	Required	Description
name	string	Yes	The name

Returns: Node | null

toSexp()

Return the S-expression form of this node’s subtree.

Signature:

toSexp(): string

Example:

const result = instance.toSexp();

Returns: string

walk()

Return a TreeCursor positioned at this node.

Signature:

walk(): TreeCursor

Example:

const result = instance.walk();

Returns: TreeCursor

---

PackConfig

Configuration for the tree-sitter language pack.

Controls cache directory and which languages to pre-download. Can be loaded from a TOML file, constructed programmatically, or passed as a dict/object from language bindings.

Field	Type	Default	Description
cacheDir	string | null	null	Override the BASE directory the parser cache lives under. This is a base, not the final library path: the crate appends tree-sitter-language-pack/v{version}/libs to it, exactly as it does to the platform default. So cache_dir = "/tmp/my-parsers" resolves to /tmp/my-parsers/tree-sitter-language-pack/v{version}/libs/. The suffix is not cosmetic. It keeps the whole cache tree — manifest, bundles and lock file included — inside a directory this library owns and versions. Earlier releases used this path verbatim, which put those files in the configured directory’s PARENT and let a cache built by one crate version be reused by another. Default base: the platform cache dir, e.g. ~/.cache on Linux.
languages	Array<string> | null	[]	Languages to pre-download on init. Each entry is a language name (e.g. "python", "rust").
groups	Array<string> | null	[]	Language groups to pre-download. Group names come from the remote manifest, so the valid set is not fixed by this library; the published manifest currently defines only "all". Call manifest_groups to enumerate them. An unknown name makes init fail.

---

Parser

A tree-sitter parser configured for one language at a time.

Methods

new()

Construct a new parser with no language set and no parse limits.

Call Parser.set_language before parsing. Limits are opt-in via set_max_source_bytes and set_parse_timeout_ms; both default to unbounded so that existing callers are unaffected.

Signature:

static new(): Parser

Example:

const result = Parser.new();

Returns: Parser

setMaxSourceBytes()

Refuse to parse sources longer than max_bytes.

null (the default) means no limit. Over-limit input makes parse and parse_bytes return null after emitting a WARN; input is never silently truncated.

See RECOMMENDED_MAX_SOURCE_BYTES.

Signature:

setMaxSourceBytes(maxBytes: number): void

Example:

instance.setMaxSourceBytes(42);

Parameters:

Name	Type	Required	Description
maxBytes	number | null	No	The max bytes

Returns: No return value.

setParseTimeoutMs()

Cancel a parse that exceeds timeout_ms milliseconds of wall clock.

null (the default) means no budget. Cancellation runs through tree-sitter’s parse progress callback, so it is granular to that callback’s interval rather than exact.

See RECOMMENDED_PARSE_TIMEOUT_MS.

Signature:

setParseTimeoutMs(timeoutMs: number): void

Example:

instance.setParseTimeoutMs(42);

Parameters:

Name	Type	Required	Description
timeoutMs	number | null	No	The timeout ms

Returns: No return value.

setLanguage()

Configure the parser to use the language identified by name (e.g. "python").

Resolves the language through the global registry — auto-downloading if necessary, when the download feature is enabled.

Errors:

Returns Error.LanguageNotFound if the language is not recognized, or Error.ParserSetup if the language ABI is incompatible.

Signature:

setLanguage(name: string): void

Example:

instance.setLanguage("value");

Parameters:

Name	Type	Required	Description
name	string	Yes	The name

Returns: No return value.

Errors: Throws Error with a descriptive message.

parse()

Parse a UTF-8 source string.

Returns null if no language is set, if the parse was cancelled by the configured timeout, or if the source exceeds the configured size limit. Each non-parse outcome is logged, so an empty result is never silent.

Concurrency

Parsing runs fully in parallel across threads for almost every language — no lock is taken. The exception is the small set of grammars whose external scanner keeps mutable process-global state (currently just properties): parses of that language are serialized against each other through an internal per-language lock, so that concurrent threads can’t corrupt shared scanner state. Every other language is unaffected by that lock and never waits on it.

Signature:

parse(source: string): Tree | null

Example:

const result = instance.parse("value");

Parameters:

Name	Type	Required	Description
source	string	Yes	The source

Returns: Tree | null

parseBytes()

Parse a raw byte slice.

Same outcomes as parse, including the concurrency behaviour documented there.

Signature:

parseBytes(source: Buffer): Tree | null

Example:

const result = instance.parseBytes(new Uint8Array([100, 97, 116, 97]));

Parameters:

Name	Type	Required	Description
source	Buffer	Yes	The source

Returns: Tree | null

reset()

Reset internal state. The next call to parse will not be incremental.

Signature:

reset(): void

Example:

instance.reset();

Returns: No return value.

---

Point

A source position — row + column, zero-indexed.

Field	Type	Default	Description
row	number	—	Zero-indexed row number.
column	number	—	Zero-indexed column, counted in bytes from the start of the row. This is tree_sitter.Point.column verbatim, and tree-sitter defines it as a byte offset — not characters, and not UTF-16 code units. Measured on a row of the form x = '<c>' where <c> is a single 4-byte character (an emoji), the string node reports columns 4..10, identical to its byte range; the character columns would be 4..7 and the UTF-16 columns 4..8. Anything that builds LSP positions (UTF-16) or editor caret columns (characters) from this field is silently wrong on every row containing a non-ASCII byte, and must re-measure the row against the source text instead. Earlier releases documented this field as UTF-16 code units; that was never what the value contained.

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ProcessConfig

Configuration for the process() function.

Controls which analysis features are enabled and whether chunking is performed.

Field	Type	Default	Description
language	string	""	Language name (required).
structure	boolean	true	Extract structural items (functions, classes, etc.). Default: true.
imports	boolean	true	Extract import statements. Default: true.
exports	boolean	true	Extract export statements. Default: true.
comments	boolean	false	Extract comments. Default: false.
docstrings	boolean	false	Extract docstrings. Default: false.
symbols	boolean	false	Extract symbol definitions. Default: false.
diagnostics	boolean	false	Include parse diagnostics. Default: false.
chunkMaxSize	number | null	null	Maximum chunk size in bytes. null disables chunking. Some(0) is rejected by ProcessConfig.validate with Error.InvalidRange. A zero-sized chunk limit previously produced an empty chunk list and silently discarded the whole source; use null to mean “do not chunk”.
dataExtraction	boolean	false	Extract hierarchical key/value data tree from data-format files. Default: false. When true, ProcessResult.data is populated with a DataNode tree for supported languages: JSON, YAML, TOML, .properties, HCL/HOCON, INI, editorconfig, KDL, CUE, CSV, PSV, PO, nginx config, Caddy config, XML, and DTD. For languages outside this set the field is left as null.
maxSourceBytes	number | null	null	Reject source longer than this many bytes instead of parsing it. Default: null (unbounded). Tree-sitter allocates and walks proportionally to input size, so an unbounded parse of attacker-supplied input is a denial-of-service vector. The default stays unbounded for backward compatibility; services handling untrusted input should opt in, e.g. with RECOMMENDED_MAX_SOURCE_BYTES. Exceeding the limit fails the call with Error.InvalidRange — the source is never silently truncated.
parseTimeoutMs	number | null	null	Wall-clock budget for the parse step, in milliseconds. Default: null (no timeout). Enforced through tree-sitter’s parse progress callback, which the parser invokes periodically; cancellation is therefore granular to that callback interval rather than exact. A parse that exceeds the budget fails with Error.ParseTimeout.

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ProcessResult

Complete analysis result from processing a source file.

Contains metrics, structural analysis, imports/exports, comments, docstrings, symbols, diagnostics, and optionally chunked code segments. Fields are populated based on the ProcessConfig flags.

Field	Type	Default	Description
language	string	—	The language name used to parse the source file.
metrics	FileMetrics	—	File-level metrics (line counts, byte size, error count).
structure	Array<StructureItem>	[]	Top-level structural items (functions, classes, etc.).
imports	Array<ImportInfo>	[]	Import statements extracted from the source.
exports	Array<ExportInfo>	[]	Export statements extracted from the source.
comments	Array<CommentInfo>	[]	Comments extracted from the source.
docstrings	Array<DocstringInfo>	[]	Docstrings extracted from the source.
symbols	Array<SymbolInfo>	[]	Symbol definitions (variables, types, functions) extracted from the source.
diagnostics	Array<Diagnostic>	[]	Parse diagnostics (syntax errors, missing nodes) from tree-sitter.
chunks	Array<CodeChunk>	[]	Syntax-aware code chunks produced when chunking is enabled.
data	DataNode | null	null	Hierarchical data tree extracted when config.data_extraction is true. Populated for supported data-format languages (JSON, YAML, TOML, properties, HCL, INI, XML, CSV, and more). null when data_extraction is false (the default) or when the language is not a recognised data format. See DataNode for the shape of the returned tree.

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Span

Byte and line/column range in source code.

Represents both byte offsets (for slicing) and human-readable line/column positions (for display and diagnostics).

Field	Type	Default	Description
startByte	number	—	Inclusive start byte offset in the source.
endByte	number	—	Exclusive end byte offset in the source.
startLine	number	—	Zero-indexed line number of the span’s start.
startColumn	number	—	Zero-indexed column of the span’s start, counted in bytes from the start of the line — not characters, not UTF-16 code units.
endLine	number	—	Zero-indexed line number of the span’s end.
endColumn	number	—	Zero-indexed column of the span’s end, counted in bytes from the start of the line — not characters, not UTF-16 code units.

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StructureItem

A structural item (function, class, struct, etc.) in source code.

Field	Type	Default	Description
kind	StructureKind	StructureKind.Function	The kind of structural item.
name	string | null	null	The declared name of the item, if present.
visibility	string | null	null	Visibility modifier (e.g., "pub", "public", "private").
span	Span	—	Source span covering the entire item declaration.
children	Array<StructureItem>	[]	Nested structural items (e.g., methods within a class).
decorators	Array<string>	[]	Decorator or attribute names applied to the item. Reserved: not yet populated. Always empty, for every language. Recognising a decorator requires per-language grammar knowledge (a Python decorated_definition wrapper, Java/C# annotations, Rust attributes each have a different shape), which no extractor here implements yet. The field is kept rather than removed so a consumer’s deserializer does not need updating once it is.
docComment	string | null	null	Documentation comment attached to the item, if any. The text of the comment (or run of comments) immediately preceding the item, with no blank line in between, when that comment is classified as a doc comment. Multiple adjacent single-line doc comments (Rust ///) are joined with \n in source order. Populated for Rust (//////!), Java (/** */), and JavaScript/ TypeScript (/** */). null for every other language, and for a preceding comment that is not in doc-comment form (a plain # comment in Python, Ruby, or Elixir) — Python’s docstring convention is captured separately, as DocstringInfo, not through this field.
signature	string | null	null	Full signature text of the item (e.g., function parameters and return type). The item’s own source text from its start up to the start of its body (see StructureItem.body_span), trimmed of trailing whitespace — for example fn add(a: i32, b: i32) -> i32 for a Rust function whose body is { a + b }. null only when that text is empty, which does not happen for any item StructureKind currently reports. Populated for every language and kind this library extracts structure for, since it is derived from body_span’s boundary rather than per-language syntax.
bodySpan	Span | null	null	Source span covering only the body of the item, if distinct from the declaration.

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SymbolInfo

A symbol (variable, function, type, etc.) extracted from source code.

Field	Type	Default	Description
name	string	—	The name of the symbol.
kind	SymbolKind	SymbolKind.Variable	The kind of symbol (variable, function, class, etc.).
span	Span	—	Source span covering the symbol definition.
typeAnnotation	string | null	null	Explicit type annotation, if present in the source.
doc	string | null	null	Documentation comment immediately preceding this symbol, resolved by the same walk StructureItem.doc_comment uses (see doc_comment_at) — never hard-coded null. Populated for Rust (//////!), Java (/** */), and JavaScript/ TypeScript (/** */) — the languages whose comment classification recognizes a doc-kind comment. null for every other language (e.g. Python, Go, Ruby, which have no doc-kind comment classification), and also null when a symbol in a supported language simply has no doc comment immediately above it.

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Tree

A parsed syntax tree. Cheap to clone (refcount bump).

Methods

rootNode()

Return the root Node of this tree.

Signature:

rootNode(): Node

Example:

const result = instance.rootNode();

Returns: Node

walk()

Return a TreeCursor positioned at the root.

Signature:

walk(): TreeCursor

Example:

const result = instance.walk();

Returns: TreeCursor

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TreeCursor

A cursor for traversing a Tree.

Methods

node()

Return the Node at the cursor’s current position.

Signature:

node(): Node

Example:

const result = instance.node();

Returns: Node

gotoFirstChild()

Move the cursor to the first child of the current node. Returns true if a child existed.

Signature:

gotoFirstChild(): boolean

Example:

const result = instance.gotoFirstChild();

Returns: boolean

gotoParent()

Move the cursor to the parent of the current node. Returns true if a parent existed.

Signature:

gotoParent(): boolean

Example:

const result = instance.gotoParent();

Returns: boolean

gotoNextSibling()

Move the cursor to the next sibling of the current node. Returns true if a sibling existed.

Signature:

gotoNextSibling(): boolean

Example:

const result = instance.gotoNextSibling();

Returns: boolean

fieldName()

Return the field name for the current node, if any.

Signature:

fieldName(): string | null

Example:

const result = instance.fieldName();

Returns: string | null

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Enums

DataNodeKind

The kind of a data node extracted from a data-format file.

Classifies each node in the hierarchical DataNode tree returned when data_extraction is enabled on ProcessConfig.

Wire format (public JSON contract)

Unit variants serialize as a bare string ("KeyValue"). DO NOT add #[serde(tag = "...")] or rename variants — every language binding has a hand-written deserializer matching this exact shape, and any change breaks all bindings’ process() tests simultaneously. Covered by tests/wire_format.rs.

Value	Description
KeyValue	A key/value pair or mapping (json/toml/properties/yaml/hcl/cue/kdl pair, or a wrapper “object”/“mapping” container).
Element	An XML element with a tag name in key and attributes in attributes.
Sequence	A positional sequence item (JSON array element, YAML block sequence item, CSV/PSV row or cell).

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StructureKind

The kind of structural item found in source code.

Categorizes top-level and nested declarations such as functions, classes, structs, enums, traits, and more. Use Other for language-specific constructs that do not fit a standard category.

Wire format (public JSON contract)

Unit variants serialize as a bare string ("Function"); the Other variant serializes as a single-keyed object ({"Other": "macro"}). DO NOT add #[serde(tag = "...")] or rename variants — every language binding has a hand-written deserializer matching this exact shape, and any change breaks all bindings’ process() tests simultaneously. Covered by tests/wire_format.rs.

Value	Description
Function	A free-standing or associated function.
Method	A method defined inside a class, struct, trait, or impl block.
Class	A class definition.
Struct	A struct definition.
Interface	An interface or protocol definition.
Enum	An enum definition.
Module	A module or package declaration.
Trait	A trait definition.
Impl	An impl block (Rust) or similar implementation block.
Namespace	A namespace declaration.
Other	A language-specific construct that does not fit any standard category. — Fields: 0: string

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CommentKind

The kind of a comment found in source code.

Distinguishes between single-line comments, block (multi-line) comments, and documentation comments.

Value	Description
Line	A single-line comment (e.g., // ... or # ...).
Block	A block or multi-line comment using slash-star delimiters.
Doc	A documentation comment such as /// ... or slash-double-star block.

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DocstringFormat

The format of a docstring extracted from source code.

Identifies the docstring convention used, which varies by language (e.g., Python triple-quoted strings, JSDoc, Rustdoc /// comments).

Wire format (public JSON contract)

Unit variants serialize as a bare string ("JSDoc"); the Other variant serializes as a single-keyed object ({"Other": "rst"}). DO NOT add #[serde(tag = "...")]. Covered by tests/wire_format.rs.

Value	Description
PythonTripleQuote	Python triple-quoted string docstring ("""...""").
JsDoc	JavaScript/TypeScript JSDoc block comment (opens with two stars, closes with star-slash).
Rustdoc	Rust /// or //! doc comment.
GoDoc	Go doc comment (a comment block immediately preceding a declaration).
JavaDoc	Java Javadoc block comment (opens with two stars, closes with star-slash).
Other	A language-specific docstring format not covered by the standard variants. — Fields: 0: string

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ExportKind

The kind of an export statement found in source code.

Covers named exports, default exports, and re-exports from other modules.

Value	Description
Named	A named export (e.g., export { foo }).
Default	A default export (e.g., export default foo).
ReExport	A re-export from another module (e.g., export { foo } from 'bar').

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SymbolKind

The kind of a symbol definition found in source code.

Categorizes symbol definitions such as variables, constants, functions, classes, types, interfaces, enums, and modules.

Wire format (public JSON contract)

Unit variants serialize as a bare string ("Function"); the Other variant serializes as a single-keyed object ({"Other": "macro"}). DO NOT add #[serde(tag = "...")]. Covered by tests/wire_format.rs.

Value	Description
Variable	A variable binding.
Constant	A constant (immutable binding).
Function	A function definition.
Class	A class definition.
Type	A type alias or typedef.
Interface	An interface definition.
Enum	An enum definition.
Module	A module declaration.
Other	A symbol kind not covered by the standard variants. — Fields: 0: string

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DiagnosticSeverity

Severity level of a diagnostic produced during parsing.

Used to classify parse errors, warnings, and informational messages found in the syntax tree.

Value	Description
Error	A parse error (e.g., an ERROR or MISSING node in the tree).
Warning	A warning-level diagnostic.
Info	An informational diagnostic.

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Errors

Error

Errors that can occur when using the tree-sitter language pack.

Covers language lookup failures, parse errors, query errors, and I/O issues. Feature-gated variants are included when config, download, or related features are enabled.

Matching on Error

The set of variants is not stable: new failure modes are added in minor releases, and Io, Json, and Toml exist only under certain feature combinations, so the variant set a downstream crate sees depends on which features it enables. Downstream matches must therefore carry a _ arm; #[non_exhaustive] makes the compiler enforce that instead of letting a feature change silently break a build.

C ABI error codes

Each variant alef can see carries an explicit alef(error_code = N) allocation that becomes a member of the generated AlefFfiErrorCode C enum. These numbers are a public ABI contract: an allocated number is never reused after its variant is removed, and a variant’s number never changes, because C callers compare against the value, not the name. New variants take the next free number. 0-4 are reserved by alef, so allocation starts at 100. An unannotated variant is emitted as the unknown code rather than as itself, which silently flattens the taxonomy — annotate every new variant.

Errors are thrown as plain Error objects with descriptive messages.

Variant	Description
LanguageNotFound	The requested language name (or alias) was not found in the registry.
DynamicLoad	A dynamic shared library could not be loaded at runtime.
NullLanguagePointer	The tree-sitter language function returned a null pointer for the given language name.
ParserSetup	The language could not be applied to the parser (e.g., ABI version mismatch).
LockPoisoned	An internal RwLock or Mutex was poisoned by a previous panic.
Config	A configuration file or value was invalid or could not be applied.
ParseFailed	The tree-sitter parser returned no tree for the given source input.
ParseTimeout	The parse was cancelled because it exceeded its configured wall-clock budget. Raised only when a budget is configured — see ProcessConfig.parse_timeout_ms, which defaults to null.
QueryError	A tree-sitter query could not be compiled or executed.
InvalidRange	A byte range was invalid (e.g., end before start, or out of bounds).
Download	A parser download from GitHub releases failed.
ChecksumMismatch	The downloaded file’s SHA-256 digest did not match the manifest’s expected value.
CacheLock	The cross-process download cache lock file could not be acquired or created.

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