feat: sanity check to validate entrypoints

src/package.ts

@@ -916,6 +916,32 @@ class LicenseProcessor extends BaseProcessor {
 	}
 }
 
+class LaunchEntryPointProcessor extends BaseProcessor {
+	private entryPoints: Set<string> = new Set<string>();
+
+	constructor(manifest: Manifest) {
+		super(manifest);
+		if (manifest.main) {
+			this.entryPoints.add(util.normalize(path.join('extension', manifest.main)));
+		}
+		if (manifest.browser) {
+			this.entryPoints.add(util.normalize(path.join('extension', manifest.browser)));
+		}
+	}
+
+	onFile(file: IFile): Promise<IFile> {
+		this.entryPoints.delete(util.normalize(file.path));
+		return Promise.resolve(file);
+	}
+
+	async onEnd(): Promise<void> {
+		if (this.entryPoints.size > 0) {
+			const files: string = [...this.entryPoints].join(',\n  ');
+			throw new Error(`Extension entrypoint(s) missing. Make sure these files exist and aren't ignored by '.vscodeignore':\n  ${files}`);
+		}
+	}
+}
+
 class IconProcessor extends BaseProcessor {
 	private icon: string | undefined;
 	private didFindIcon = false;
@@ -1498,6 +1524,7 @@ export function createDefaultProcessors(manifest: Manifest, options: IPackageOpt
 		new TagsProcessor(manifest),
 		new ReadmeProcessor(manifest, options),
 		new ChangelogProcessor(manifest, options),
+		new LaunchEntryPointProcessor(manifest),
 		new LicenseProcessor(manifest),
 		new IconProcessor(manifest),
 		new NLSProcessor(manifest),

src/test/package.test.ts

@@ -1794,6 +1794,28 @@ describe('toContentTypes', () => {
 	});
 });
 
+describe('LaunchEntryPointProcessor', () => {
+	it('should detect when declared entrypoint is not in package', async () => {
+		const manifest = createManifest({
+			main: 'main.js',
+		});
+		const files = [{ path: 'extension/browser.js', contents: Buffer.from('') }];
+		let didErr = false;
+		try {
+			await _toVsixManifest(manifest, files);
+		} catch (err: any) {
+			const message = err.message;
+			didErr = message.includes('entrypoint(s) missing') && message.includes('main.js');
+		}
+		assert.ok(didErr);
+	});
+
+	it('should accept manifest if no entrypoints defined', async () => {
+		const manifest = createManifest({});
+		const files = [{ path: 'extension/something.js', contents: Buffer.from('') }];
+		await _toVsixManifest(manifest, files);
+	});
+});
 describe('ManifestProcessor', () => {
 	it('should ensure that package.json is writable', async () => {
 		const root = fixture('uuid');