ast-grep

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API Reference ​

ast-grep currently has an experimental API for Node.js.

You can see API usage guide for more details.

NAPI ​

Please see the link for up-to-date type declaration.

https://github.com/ast-grep/ast-grep/blob/main/crates/napi/index.d.ts

Supported Languages ​

@ast-grep/napi supports JS ecosystem languages by default. More custom languages can be loaded via registerDynamicLanguage.

Type ​

ts
export const enum Lang {
  Html = 'Html',
  JavaScript = 'JavaScript',
  Tsx = 'Tsx',
  Css = 'Css',
  TypeScript = 'TypeScript',
}

// More custom languages can be loaded
// see https://github.com/ast-grep/langs
type CustomLang = string & {}

CustomLang is not widely used now. If you have use case and needs support, please file an issue in the @ast-grep/langs repository.

Main functions ​

You can use parse to transform a string to ast-grep's main object SgRoot. ast-grep also provides other utility for parse kind string and construct pattern.

ts
/** Parse a string to an ast-grep instance */
export function parse(lang: Lang, src: string): SgRoot
/** Get the `kind` number from its string name. */
export function kind(lang: Lang, kindName: string): number
/** Compile a string to ast-grep Pattern. */
export function pattern(lang: Lang, pattern: string): NapiConfig

Example ​

ts
import { parse, Lang } from '@ast-grep/napi'

const ast = parse(Lang.JavaScript, source)
const root = ast.root()
root.find("console.log")

SgRoot ​

You will get an SgRoot instance when you parse(lang, string).

SgRoot can also be accessed in lang.findInFiles's callback by calling node.getRoot().

In the latter case, sgRoot.filename() will return the path of the matched file.

Type ​

ts
/** Represents the parsed tree of code. */
class SgRoot {
  /** Returns the root SgNode of the ast-grep instance. */
  root(): SgNode
  /**
   * Returns the path of the file if it is discovered by ast-grep's `findInFiles`.
   * Returns `"anonymous"` if the instance is created by `parse(lang, source)`.
   */
  filename(): string
}

Example ​

ts
import { parse, Lang } from '@ast-grep/napi'

const ast = parse(Lang.JavaScript, source)
const root = ast.root()
root.find("console.log")

SgNode ​

The main interface to traverse the AST.

Type ​

Most methods are self-explanatory. Please submit a new issue if you find something confusing.

ts
class SgNode {
  // Read node's information
  range(): Range
  isLeaf(): boolean
  isNamed(): boolean
  isNamedLeaf(): boolean
  kind(): string
  // check if node has kind
  is(kind: string): boolean
  // for TypeScript type narrow
  kindToRefine: string
  text(): string
  // Check if node meets certain patterns
  matches(m: string): boolean
  inside(m: string): boolean
  has(m: string): boolean
  precedes(m: string): boolean
  follows(m: string): boolean
  // Get nodes' matched meta variables
  getMatch(m: string): SgNode | null
  getMultipleMatches(m: string): Array<SgNode>
  // Get node's SgRoot
  getRoot(): SgRoot
  // Traverse node tree
  children(): Array<SgNode>
  find(matcher: string | number | NapiConfig): SgNode | null
  findAll(matcher: string | number | NapiConfig): Array<SgNode>
  field(name: string): SgNode | null
  parent(): SgNode | null
  child(nth: number): SgNode | null
  ancestors(): Array<SgNode>
  next(): SgNode | null
  nextAll(): Array<SgNode>
  prev(): SgNode | null
  prevAll(): Array<SgNode>
  // Edit
  replace(text: string): Edit
  commitEdits(edits: Edit[]): string
}

Some methods have more sophisticated type signatures for the ease of use. See the source code and our tech blog

NapiConfig ​

NapiConfig is used in find or findAll.

Type ​

NapiConfig has similar fields as the rule config.

ts
interface NapiConfig {
  rule: object
  constraints?: object
  language?: FrontEndLanguage
  transform?: object
  utils?: object
}

FindConfig ​

FindConfig is used in findInFiles.

Type ​

ts
interface FindConfig {
  // You can search multiple paths
  // ast-grep will recursively find all files under the paths.
  paths: Array<string>
  // Specify what nodes will be matched
  matcher: NapiConfig
}

Edit ​

Edit is used in replace and commitEdits.

ts
interface Edit {
  startPos: number
  endPos: number
  insertedText: string
}

Useful Examples ​

Language Object (deprecated) Deprecated ​

language objects are deprecated

ast-grep/napi also has special language objects for html, js and css. They are deprecated and will be removed in the next version.

A language object has following methods.

ts
/**
 * @deprecated language specific objects are deprecated
 * use the equivalent functions like `parse` in @ast-grep/napi
 */
export declare namespace js {
  /** @deprecated use `parse(Lang.JavaScript, src)` instead */
  export function parse(src: string): SgRoot
  /** @deprecated use `parseAsync(Lang.JavaScript, src)` instead */
  export function parseAsync(src: string): Promise<SgRoot>
  /** @deprecated use `kind(Lang.JavaScript, kindName)` instead */
  export function kind(kindName: string): number
  /** @deprecated use `pattern(Lang.JavaScript, p)` instead */
  export function pattern(pattern: string): NapiConfig
  /** @deprecated use `findInFiles(Lang.JavaScript, config, callback)` instead */
  export function findInFiles(
    config: FindConfig,
    callback: (err: null | Error, result: SgNode[]) => void
  ): Promise<number>
}

Example ​

ts
import { js } from '@ast-grep/napi'

const source = `console.log("hello world")`
const ast = js.parse(source)

Python API ​

SgRoot ​

The entry point object of ast-grep. You can use SgRoot to parse a string into a syntax tree.

python
class SgRoot:
    def __init__(self, src: str, language: str) -> None: ...
    def root(self) -> SgNode: ...

SgNode ​

Most methods are self-explanatory. Please submit a new issue if you find something confusing.

python
class SgNode:
    # Node Inspection
    def range(self) -> Range: ...
    def is_leaf(self) -> bool: ...
    def is_named(self) -> bool: ...
    def is_named_leaf(self) -> bool: ...
    def kind(self) -> str: ...
    def text(self) -> str: ...

    # Refinement
    def matches(self, **rule: Unpack[Rule]) -> bool: ...
    def inside(self, **rule: Unpack[Rule]) -> bool: ...
    def has(self, **rule: Unpack[Rule]) -> bool: ...
    def precedes(self, **rule: Unpack[Rule]) -> bool: ...
    def follows(self, **rule: Unpack[Rule]) -> bool: ...
    def get_match(self, meta_var: str) -> Optional[SgNode]: ...
    def get_multiple_matches(self, meta_var: str) -> List[SgNode]: ...
    def get_transformed(self, meta_var: str) -> Optional[str]: ...
    def __getitem__(self, meta_var: str) -> SgNode: ...

    # Search
    @overload
    def find(self, config: Config) -> Optional[SgNode]: ...
    @overload
    def find(self, **kwargs: Unpack[Rule]) -> Optional[SgNode]: ...
    @overload
    def find_all(self, config: Config) -> List[SgNode]: ...
    @overload
    def find_all(self, **kwargs: Unpack[Rule]) -> List[SgNode]: ...

    # Tree Traversal
    def get_root(self) -> SgRoot: ...
    def field(self, name: str) -> Optional[SgNode]: ...
    def parent(self) -> Optional[SgNode]: ...
    def child(self, nth: int) -> Optional[SgNode]: ...
    def children(self) -> List[SgNode]: ...
    def ancestors(self) -> List[SgNode]: ...
    def next(self) -> Optional[SgNode]: ...
    def next_all(self) -> List[SgNode]: ...
    def prev(self) -> Optional[SgNode]: ...
    def prev_all(self) -> List[SgNode]: ...

    # Edit
    def replace(self, new_text: str) -> Edit: ...
    def commit_edits(self, edits: List[Edit]) -> str: ...

Rule ​

The Rule object is a Python representation of the YAML rule object in the CLI. See the reference.

python
class Pattern(TypedDict):
    selector: str
    context: str

class Rule(TypedDict, total=False):
    # atomic rule
    pattern: str | Pattern
    kind: str
    regex: str

    # relational rule
    inside: Relation
    has: Relation
    precedes: Relation
    follows: Relation

    # composite rule
    all: List[Rule]
    any: List[Rule]
    # pseudo code below for demo.
    "not": Rule # Python does not allow "not" keyword as attribute
    matches: str

# Relational Rule Related
StopBy = Union[Literal["neighbor"], Literal["end"], Rule]
class Relation(Rule, total=False):
    stopBy: StopBy
    field: str

Config ​

The Config object is similar to the YAML rule config in the CLI. See the reference.

python
class Config(TypedDict, total=False):
    rule: Rule
    constraints: Dict[str, Mapping]
    utils: Dict[str, Rule]
    transform: Dict[str, Mapping]

Edit ​

Edit is used in replace and commitEdits.

python
class Edit:
    # The start position of the edit
    start_pos: int
    # The end position of the edit
    end_pos: int
    # The text to be inserted
    inserted_text: str

Rust API ​

Rust API is not stable yet. The following link is only for those who are interested in modifying ast-grep's source.

https://docs.rs/ast-grep-core/latest/ast_grep_core/

Made with ❤️ with Rust

Copyright © 2022-present Herrington Darkholme