ts-patch

What is ts-patch?

ts-patch is a tool that allows you to patch the TypeScript compiler (tsc) to enable custom transformers and other advanced features. It is particularly useful for developers who need to extend the capabilities of TypeScript beyond what is natively supported.

What are ts-patch's main functionalities?

Custom Transformers

This feature allows you to apply custom transformers to the TypeScript compiler. By patching the compiler, you can specify custom transformers in your tsconfig.json file, enabling advanced code transformations during the compilation process.

const { patch, unpatch } = require('ts-patch');

// Apply the patch
patch();

// Now you can use custom transformers in your tsconfig.json
// tsconfig.json
{
  "compilerOptions": {
    "plugins": [
      { "transform": "./path/to/your/transformer" }
    ]
  }
}

// Unpatch when done
unpatch();

Advanced Compiler Options

This feature allows you to enable advanced compiler options that are not natively supported by TypeScript. By patching the compiler, you can use options like experimental decorators and emit decorator metadata.

const { patch, unpatch } = require('ts-patch');

// Apply the patch
patch();

// Now you can use advanced compiler options in your tsconfig.json
// tsconfig.json
{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  }
}

// Unpatch when done
unpatch();

Integration with Build Tools

This feature allows you to integrate ts-patch with various build tools like Webpack. By patching the TypeScript compiler, you can use custom transformers and advanced compiler options in your build process.

const { patch, unpatch } = require('ts-patch');

// Apply the patch
patch();

// Now you can integrate ts-patch with build tools like Webpack
// webpack.config.js
const path = require('path');

module.exports = {
  entry: './src/index.ts',
  module: {
    rules: [
      {
        test: /\.tsx?$/,
        use: 'ts-loader',
        exclude: /node_modules/
      }
    ]
  },
  resolve: {
    extensions: ['.tsx', '.ts', '.js']
  },
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist')
  }
};

// Unpatch when done
unpatch();

Other packages similar to ts-patch

ttypescript

ttypescript is a fork of the TypeScript compiler that allows you to use custom transformers directly in your tsconfig.json. It is similar to ts-patch in that it enables advanced TypeScript features, but it requires you to use a different compiler binary.

babel-plugin-transform-typescript-metadata

babel-plugin-transform-typescript-metadata is a Babel plugin that adds support for TypeScript metadata reflection. While it doesn't patch the TypeScript compiler, it provides similar functionality by enabling advanced TypeScript features through Babel.

typescript-transform-paths

typescript-transform-paths is a TypeScript transformer that rewrites module paths based on the paths specified in tsconfig.json. It is similar to ts-patch in that it allows for custom transformations, but it focuses specifically on module path rewriting.

README

ts-patch

Patch typescript to allow custom transformers (plugins) during build.

Plugins are specified in tsconfig.json, or provided programmatically in CompilerOptions.

Migrating from ttypescript is easy! See: Method 1: Live Compiler

Features

• Patch typescript installation via on-the-fly, in-memory patching or as a persistent patch
• Can patch individual libraries (see ts-patch /?)
• Hook build process by transforming the Program (see: Transforming Program)
• Add, remove, or modify diagnostics (see: Altering Diagnostics)
• Fully compatible with legacy ttypescript projects
• (new) Experimental support for ES Module based transformers

Table of Contents

• ts-patch
  • Features
• Table of Contents
• Installation
• Usage
  • Method 1: Live Compiler
  • Method 2: Persistent Patch
• Configuration
  • Plugin Options
• Writing Transformers
  • Source Transformers
    • Source Transformer Entry Point
    • Source Transformer Example
    • Altering Diagnostics
    • Note
  • Program Transformers
    • Program Transformer Entry Point
    • Configuring Program Transformers
    • Program Transformer Example
  • Plugin Package Configuration
    • Example
  • Resources
    • Recommended Reading
    • Recommended Tools
    • Discussion
• Advanced Options
• Maintainers
  • Help Wanted
• License

Installation

1. Install package

<yarn|npm|pnpm> add -D ts-patch

Usage

Method 1: Live Compiler

The live compiler patches on-the-fly, each time it is run.

Via commandline: Simply use tspc (instead of tsc)

With tools such as ts-node, webpack, ts-jest, etc: specify the compiler as ts-patch/compiler

Method 2: Persistent Patch

Persistent patch modifies the typescript installation within the node_modules path. It requires additional configuration to remain persisted, but it carries less load time and complexity compared to the live compiler.

1. Install the patch

# For advanced options, see: ts-patch /?
ts-patch install

1. Add prepare script (keeps patch persisted after npm install)

package.json

{
 /* ... */
 "scripts": {
   "prepare": "ts-patch install -s"
 }
}

Configuration

tsconfig.json: Add transformers to compilerOptions in plugins array.

Examples

{
    "compilerOptions": {
        "plugins": [
            // Source Transformers
            { "transform": "transformer-module" },
            { "transform": "transformer2", "extraOption": 123 },
            { "transform": "trans-with-mapping", "resolvePathAliases": true },
            { "transform": "esm-transformer", "isEsm": true },

            // Program Transformer
            { "transform": "transformer-module5", "transformProgram": true }
        ]
    }
}

Plugin Options

Option	Type	Description
transform	string	Module name or path to transformer (*.ts or *.js)
after	boolean	Apply transformer after stock TS transformers
afterDeclarations	boolean	Apply transformer to declaration (*.d.ts) files
transformProgram	boolean	Transform Program during ts.createProgram() (see: Program Transformers)
isEsm	boolean	Transformer is ES Module (note: experimental — requires esm)
resolvePathAliases	boolean	Resolve path aliases in transformer (requires tsconfig-paths)
type	string	See: Source Transformer Entry Point (default: 'program')
import	string	Name of exported transformer function (defaults to default export)
tsConfig	string	tsconfig.json file for transformer (allows specifying compileOptions, path mapping support, etc)
...		Provide your own custom options, which will be passed to the transformer

Note: Required options are bold

Writing Transformers

For an overview of the typescript compiler (such as what a SourceFile and Program is) see: Typescript Compiler Notes.

Source Transformers

Source Transformers will transform the AST of SourceFiles during compilation, allowing you to alter the output of the JS or declarations files.

Source Transformer Entry Point

(program: ts.Program, config: PluginConfig, extras: TransformerExtras) => ts.TransformerFactory

PluginConfig: Type Declaration
TransformerExtras: Type Declaration
ts.TransformerFactory: (context: ts.TransformationContext) => (sourceFile: ts.SourceFile) => ts.SourceFile

Note: Additional legacy signatures are supported, but it is not recommended to develop a new transformer using them.

Source Transformer Example

Transformers can be written in JS or TS.

import type * as ts from 'typescript';
import type { TransformerExtras, PluginConfig } from 'ts-patch';

/** Changes string literal 'before' to 'after' */
export default function (program: ts.Program, pluginConfig: PluginConfig, { ts: tsInstance }: TransformerExtras) {
  return (ctx: ts.TransformationContext) => {
    const { factory } = ctx;
    
    return (sourceFile: ts.SourceFile) => {
      function visit(node: ts.Node): ts.Node {
        if (tsInstance.isStringLiteral(node) && node.text === 'before') {
          return factory.createStringLiteral('after');
        }
        return tsInstance.visitEachChild(node, visit, ctx);
      }
      return tsInstance.visitNode(sourceFile, visit);
    };
  };
}

Live Examples:

{ transform: "typescript-transform-paths" }

{ transform: "typescript-is/lib/transform-inline/transformer" }

{ transform: "typia/lib/transform" } (💻playground)

{ transform: "@nestia/core/lib/transform" }

Altering Diagnostics

Diagnostics can be altered in a Source Transformer.

To alter diagnostics you can use the following, provided from the TransformerExtras parameter:

property	description
diagnostics	Reference to Diagnostic array
addDiagnostic()	Safely add Diagnostic to diagnostics array
removeDiagnostic()	Safely remove Diagnostic from diagnostics array

Note

This alters diagnostics during emit only. If you want to alter diagnostics in your IDE as well, you'll need to create a LanguageService plugin to accompany your source transformer

Program Transformers

Sometimes you want to do more than just transform source code. For example you may want to:

• TypeCheck code after it's been transformed
• Generate code and add it to the program
• Add or remove emit files during transformation

For this, we've introduced what we call a Program Transformer. The transform action takes place during ts.createProgram, and allows re-creating the Program instance that typescript uses.

Program Transformer Entry Point

(program: ts.Program, host: ts.CompilerHost | undefined, options: PluginConfig, extras: ProgramTransformerExtras) => ts.Program

ProgramTransformerExtras >>> Type Declaration

Configuring Program Transformers

To configure a Program Transformer, supply "transformProgram": true in the config transformer entry.

Note: The before, after, and afterDeclarations options do not apply to a Program Transformer and will be ignored

See Config Example

Program Transformer Example

/** 
 * Add a file to Program
 */
import * as path from 'path';
import type * as ts from 'typescript';
import type { ProgramTransformerExtras, PluginConfig } from 'ts-patch';

export const newFile = path.resolve(__dirname, 'added-file.ts');

export default function (
  program: ts.Program, 
  host: ts.CompilerHost | undefined, 
  options: PluginConfig, 
  { ts: tsInstance }: ProgramTransformerExtras
) {
  return tsInstance.createProgram(
    /* rootNames */ program.getRootFileNames().concat([ newFile ]),
    program.getCompilerOptions(),
    host,
    /* oldProgram */ program
  );
}

Note: For a more complete example, see Transforming Program with additional AST transformations

Live Examples:

{ transform: "@typescript-virtual-barrel/compiler-plugin", transformProgram: true }

{ transform: "ts-overrides-plugin", transformProgram: true }

Plugin Package Configuration

The plugin package configuration allows you to specify custom options for your TypeScript plugin. This configuration is defined in the package.json of your plugin under the tsp property.

An example use case is enabling parseAllJsDoc if you require full JSDoc parsing in tsc for your transformer in TS v5.3+. (see: 5.3 JSDoc parsing changes)

For all available options, see the PluginPackageConfig type in plugin-types.ts

Example

{
  "name": "your-plugin-name",
  "version": "1.0.0",
  "tsp": {
    "tscOptions": {
      "parseAllJsDoc": true
    }
  }
}

Resources

Recommended Reading

• How-To: Advice for working with the TS Compiler API
• How-To: TypeScript Transformer Handbook
• Article: How to Write a TypeScript Transform (Plugin)
• Article: Creating a TypeScript Transformer

Recommended Tools

Tool	Type	Description
TS AST Viewer	Web App	Allows you to see the Node structure and other TS properties of your source code.
ts-expose-internals	NPM Package	Exposes internal types and methods of the TS compiler API

Discussion

• #compiler-internals-and-api on TypeScript Discord Server
• TSP Discussions Board

Advanced Options

(env) TSP_SKIP_CACHE

Skips patch cache when patching via cli or live compiler.

(env) TSP_COMPILER_TS_PATH

Specify typescript library path to use for ts-patch/compiler (defaults to require.resolve('typescript'))

(env) TSP_CACHE_DIR

Override patch cache directory

(cli) ts-patch clear-cache

Cleans patch cache & lockfiles

Maintainers

Ron S.

Help Wanted

If you're interested in helping and are knowledgeable with the TS compiler codebase, feel free to reach out!

License

This project is licensed under the MIT License, as described in LICENSE.md