@typescript-eslint/typescript-estree/README.md

<h1 align="center">TypeScript ESTree</h1>

<p align="center">A parser that converts TypeScript source code into an <a href="https://github.com/estree/estree">ESTree</a>-compatible form</p>

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## Getting Started

**[You can find our Getting Started docs here](../../docs/getting-started/linting/README.md)**

## About

This parser is somewhat generic and robust, and could be used to power any use-case which requires taking TypeScript source code and producing an ESTree-compatible AST.

In fact, it is already used within these hyper-popular open-source projects to power their TypeScript support:

- [ESLint](https://eslint.org), the pluggable linting utility for JavaScript and JSX
- [Prettier](https://prettier.io), an opinionated code formatter

## Installation

```sh
yarn add -D @typescript-eslint/typescript-estree
```

## API

### Parsing

#### `parse(code, options)`

Parses the given string of code with the options provided and returns an ESTree-compatible AST.

```ts
interface ParseOptions {
  /**
   * create a top-level comments array containing all comments
   */
  comment?: boolean;

  /**
   * An array of modules to turn explicit debugging on for.
   * - 'typescript-eslint' is the same as setting the env var `DEBUG=typescript-eslint:*`
   * - 'eslint' is the same as setting the env var `DEBUG=eslint:*`
   * - 'typescript' is the same as setting `extendedDiagnostics: true` in your tsconfig compilerOptions
   *
   * For convenience, also supports a boolean:
   * - true === ['typescript-eslint']
   * - false === []
   */
  debugLevel?: boolean | ('typescript-eslint' | 'eslint' | 'typescript')[];

  /**
   * Cause the parser to error if it encounters an unknown AST node type (useful for testing).
   * This case only usually occurs when TypeScript releases new features.
   */
  errorOnUnknownASTType?: boolean;

  /**
   * Absolute (or relative to `cwd`) path to the file being parsed.
   */
  filePath?: string;

  /**
   * Enable parsing of JSX.
   * For more details, see https://www.typescriptlang.org/docs/handbook/jsx.html
   *
   * NOTE: this setting does not effect known file types (.js, .jsx, .ts, .tsx, .json) because the
   * TypeScript compiler has its own internal handling for known file extensions.
   *
   * For the exact behavior, see https://github.com/typescript-eslint/typescript-eslint/tree/master/packages/parser#parseroptionsecmafeaturesjsx
   */
  jsx?: boolean;

  /**
   * Controls whether the `loc` information to each node.
   * The `loc` property is an object which contains the exact line/column the node starts/ends on.
   * This is similar to the `range` property, except it is line/column relative.
   */
  loc?: boolean;

  /*
   * Allows overriding of function used for logging.
   * When value is `false`, no logging will occur.
   * When value is not provided, `console.log()` will be used.
   */
  loggerFn?: Function | false;

  /**
   * Controls whether the `range` property is included on AST nodes.
   * The `range` property is a [number, number] which indicates the start/end index of the node in the file contents.
   * This is similar to the `loc` property, except this is the absolute index.
   */
  range?: boolean;

  /**
   * Set to true to create a top-level array containing all tokens from the file.
   */
  tokens?: boolean;
}

const PARSE_DEFAULT_OPTIONS: ParseOptions = {
  comment: false,
  errorOnUnknownASTType: false,
  filePath: 'estree.ts', // or 'estree.tsx', if you pass jsx: true
  jsx: false,
  loc: false,
  loggerFn: undefined,
  range: false,
  tokens: false,
};

declare function parse(
  code: string,
  options: ParseOptions = PARSE_DEFAULT_OPTIONS,
): TSESTree.Program;
```

Example usage:

```js
import { parse } from '@typescript-eslint/typescript-estree';

const code = `const hello: string = 'world';`;
const ast = parse(code, {
  loc: true,
  range: true,
});
```

#### `parseAndGenerateServices(code, options)`

Parses the given string of code with the options provided and returns an ESTree-compatible AST. Accepts additional options which can be used to generate type information along with the AST.

```ts
interface ParseAndGenerateServicesOptions extends ParseOptions {
  /**
   * Causes the parser to error if the TypeScript compiler returns any unexpected syntax/semantic errors.
   */
  errorOnTypeScriptSyntacticAndSemanticIssues?: boolean;

  /**
   * ***EXPERIMENTAL FLAG*** - Use this at your own risk.
   *
   * Causes TS to use the source files for referenced projects instead of the compiled .d.ts files.
   * This feature is not yet optimized, and is likely to cause OOMs for medium to large projects.
   *
   * This flag REQUIRES at least TS v3.9, otherwise it does nothing.
   *
   * See: https://github.com/typescript-eslint/typescript-eslint/issues/2094
   */
  EXPERIMENTAL_useSourceOfProjectReferenceRedirect?: boolean;

  /**
   * When `project` is provided, this controls the non-standard file extensions which will be parsed.
   * It accepts an array of file extensions, each preceded by a `.`.
   */
  extraFileExtensions?: string[];

  /**
   * Absolute (or relative to `tsconfigRootDir`) path to the file being parsed.
   * When `project` is provided, this is required, as it is used to fetch the file from the TypeScript compiler's cache.
   */
  filePath?: string;

  /**
   * Allows the user to control whether or not two-way AST node maps are preserved
   * during the AST conversion process.
   *
   * By default: the AST node maps are NOT preserved, unless `project` has been specified,
   * in which case the maps are made available on the returned `parserServices`.
   *
   * NOTE: If `preserveNodeMaps` is explicitly set by the user, it will be respected,
   * regardless of whether or not `project` is in use.
   */
  preserveNodeMaps?: boolean;

  /**
   * Absolute (or relative to `tsconfigRootDir`) paths to the tsconfig(s).
   * If this is provided, type information will be returned.
   */
  project?: string | string[];

  /**
   * If you provide a glob (or globs) to the project option, you can use this option to ignore certain folders from
   * being matched by the globs.
   * This accepts an array of globs to ignore.
   *
   * By default, this is set to ["/node_modules/"]
   */
  projectFolderIgnoreList?: string[];

  /**
   * The absolute path to the root directory for all provided `project`s.
   */
  tsconfigRootDir?: string;

  /**
   * An array of one or more instances of TypeScript Program objects to be used for type information.
   * This overrides any program or programs that would have been computed from the `project` option.
   * All linted files must be part of the provided program(s).
   */
  programs?: Program[];

  /**
   ***************************************************************************************
   * IT IS RECOMMENDED THAT YOU DO NOT USE THIS OPTION, AS IT CAUSES PERFORMANCE ISSUES. *
   ***************************************************************************************
   *
   * When passed with `project`, this allows the parser to create a catch-all, default program.
   * This means that if the parser encounters a file not included in any of the provided `project`s,
   * it will not error, but will instead parse the file and its dependencies in a new program.
   */
  createDefaultProgram?: boolean;

  /**
   * ESLint (and therefore typescript-eslint) is used in both "single run"/one-time contexts,
   * such as an ESLint CLI invocation, and long-running sessions (such as continuous feedback
   * on a file in an IDE).
   *
   * When typescript-eslint handles TypeScript Program management behind the scenes, this distinction
   * is important because there is significant overhead to managing the so called Watch Programs
   * needed for the long-running use-case.
   *
   * When allowAutomaticSingleRunInference is enabled, we will use common heuristics to infer
   * whether or not ESLint is being used as part of a single run.
   */
  allowAutomaticSingleRunInference?: boolean;

  /**
   * Path to a file exporting a custom ModuleResolver.
   */
  moduleResolver?: string;
}

interface ParserServices {
  program: ts.Program;
  esTreeNodeToTSNodeMap: WeakMap<TSESTree.Node, ts.Node | ts.Token>;
  tsNodeToESTreeNodeMap: WeakMap<ts.Node | ts.Token, TSESTree.Node>;
  hasFullTypeInformation: boolean;
}

interface ParseAndGenerateServicesResult<T extends TSESTreeOptions> {
  ast: TSESTree.Program;
  services: ParserServices;
}

const PARSE_AND_GENERATE_SERVICES_DEFAULT_OPTIONS: ParseOptions = {
  ...PARSE_DEFAULT_OPTIONS,
  errorOnTypeScriptSyntacticAndSemanticIssues: false,
  extraFileExtensions: [],
  preserveNodeMaps: false, // or true, if you do not set this, but pass `project`
  project: undefined,
  projectFolderIgnoreList: ['/node_modules/'],
  tsconfigRootDir: process.cwd(),
};

declare function parseAndGenerateServices(
  code: string,
  options: ParseOptions = PARSE_DEFAULT_OPTIONS,
): ParseAndGenerateServicesResult;
```

Example usage:

```js
import { parseAndGenerateServices } from '@typescript-eslint/typescript-estree';

const code = `const hello: string = 'world';`;
const { ast, services } = parseAndGenerateServices(code, {
  filePath: '/some/path/to/file/foo.ts',
  loc: true,
  project: './tsconfig.json',
  range: true,
});
```

#### `parseWithNodeMaps(code, options)`

Parses the given string of code with the options provided and returns both the ESTree-compatible AST as well as the node maps.
This allows you to work with both ASTs without the overhead of types that may come with `parseAndGenerateServices`.

```ts
interface ParseWithNodeMapsResult<T extends TSESTreeOptions> {
  ast: TSESTree.Program;
  esTreeNodeToTSNodeMap: ParserServices['esTreeNodeToTSNodeMap'];
  tsNodeToESTreeNodeMap: ParserServices['tsNodeToESTreeNodeMap'];
}

declare function parseWithNodeMaps(
  code: string,
  options: ParseOptions = PARSE_DEFAULT_OPTIONS,
): ParseWithNodeMapsResult;
```

Example usage:

```js
import { parseWithNodeMaps } from '@typescript-eslint/typescript-estree';

const code = `const hello: string = 'world';`;
const { ast, esTreeNodeToTSNodeMap, tsNodeToESTreeNodeMap } = parseWithNodeMaps(
  code,
  {
    loc: true,
    range: true,
  },
);
```

### `TSESTree`, `AST_NODE_TYPES` and `AST_TOKEN_TYPES`

Types for the AST produced by the parse functions.

- `TSESTree` is a namespace which contains object types representing all of the AST Nodes produced by the parser.
- `AST_NODE_TYPES` is an enum which provides the values for every single AST node's `type` property.
- `AST_TOKEN_TYPES` is an enum which provides the values for every single AST token's `type` property.

### Utilities

#### `createProgram(configFile, projectDirectory)`

This serves as a utility method for users of the `ParseOptions.programs` feature to create a TypeScript program instance from a config file.

```ts
declare function createProgram(
  configFile: string,
  projectDirectory: string = process.cwd(),
): import('typescript').Program;
```

Example usage:

```js
const tsESTree = require('@typescript-eslint/typescript-estree');

const program = tsESTree.createProgram('tsconfig.json');
const code = `const hello: string = 'world';`;
const { ast, services } = parseAndGenerateServices(code, {
  filePath: '/some/path/to/file/foo.ts',
  loc: true,
  program,
  range: true,
});
```

## Supported TypeScript Version

See the [Supported TypeScript Version](../../README.md#supported-typescript-version) section in the project root.

If you use a non-supported version of TypeScript, the parser will log a warning to the console.

**Please ensure that you are using a supported version before submitting any issues/bug reports.**

## Reporting Issues

Please check the current list of open and known issues and ensure the issue has not been reported before. When creating a new issue provide as much information about your environment as possible. This includes:

- TypeScript version
- The `typescript-estree` version

## AST Alignment Tests

A couple of years after work on this parser began, the TypeScript Team at Microsoft began [officially supporting TypeScript parsing via Babel](https://blogs.msdn.microsoft.com/typescript/2018/08/27/typescript-and-babel-7/).

I work closely with the TypeScript Team and we are gradually aligning the AST of this project with the one produced by Babel's parser. To that end, I have created a full test harness to compare the ASTs of the two projects which runs on every PR, please see [the code](https://github.com/typescript-eslint/typescript-eslint/tree/master/packages/typescript-estree/tests/ast-alignment) for more details.

## Debugging

If you encounter a bug with the parser that you want to investigate, you can turn on the debug logging via setting the environment variable: `DEBUG=typescript-eslint:*`.
I.e. in this repo you can run: `DEBUG=typescript-eslint:* yarn lint`.

## License

TypeScript ESTree inherits from the the original TypeScript ESLint Parser license, as the majority of the work began there. It is licensed under a permissive BSD 2-clause license.

## Contributing

[See the contributing guide here](../../CONTRIBUTING.md)