feat(worker-bundler): add typescript support for worker-bundler

[zebp]

Adds support for the TypeScript language service to @cloudflare/worker-bundler as well a new virtual file-system abstraction for interfacing with the code for bundled workers. This is primarily to allow efficient storage of Worker code in Durable Objects.

Example

const inputFileSystem = new InMemoryFileSystem({
  "package.json": JSON.stringify({
    dependencies: {
      "@cloudflare/workers-types": "^4.20260405.1"
    }
  }),
  "tsconfig.json": JSON.stringify({
    compilerOptions: {
      lib: ["es2024"],
      target: "ES2024",
      module: "ES2022",
      moduleResolution: "bundler",
      allowSyntheticDefaultImports: true,
      strict: true,
      skipLibCheck: true,
      types: ["@cloudflare/workers-types/index.d.ts"]
    }
  }),
  "src/index.ts": `
    const worker: ExportedHandler = {
    
    async fetch() {
        return new Response("Hello, world!");
      }
    };
    
    export default worker;
  `
});

const installResult = await installDependencies(inputFileSystem);
const { fileSystem, languageService } = await createTypescriptLanguageService({ fileSystem: inputFileSystem });

Separate ./typescript export

The TypeScript bundle is large (~5 MB minified). Importing it unconditionally from the main entry point would penalise every caller that only needs bundling. The language service is therefore exported under its own subpath:

import { createTypescriptLanguageService } from "@cloudflare/worker-bundler/typescript";

---

[changeset-bot]

🦋 Changeset detected

Latest commit: 9c53d77

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@cloudflare/worker-bundler	Minor

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commit: 9c53d77

[devin-ai-integration]

Devin Review found 1 potential issue.

View 6 additional findings in Devin Review.

[devin-ai-integration]

🔴 TypescriptFileSystem.write() throws for files not in the original root set

The write() method unconditionally calls this.typescriptEnv.updateFile(path, content), but @typescript/vfs's updateFile throws "Did not find a source file for <fileName>" when the file wasn't in the original root files passed to createVirtualTypeScriptEnvironment. This means any caller who writes a new file through the returned TypescriptFileSystem wrapper will get a runtime crash.

@typescript/vfs updateFile implementation (confirms the throw)

updateFile: function updateFile(fileName, content, optPrevTextSpan) {
  var prevSourceFile = languageService.getProgram().getSourceFile(fileName);
  if (!prevSourceFile) {
    throw new Error("Did not find a source file for " + fileName);
  }
  // ...
}

The VirtualTypeScriptEnvironment exposes both createFile(fileName, content) (for new files) and updateFile(fileName, content) (for existing files). The fix is to check getSourceFile() first and dispatch to the correct method.

Suggested change

	write(path: string, content: string): void {
	this.innerFs.write(path, content);
	this.typescriptEnv.updateFile(path, content);
	}
	write(path: string, content: string): void {
	this.innerFs.write(path, content);
	if (this.typescriptEnv.getSourceFile(path)) {
	this.typescriptEnv.updateFile(path, content);
	} else {
	this.typescriptEnv.createFile(path, content);
	}
	}

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