fix: prevent imports from folder with same name

See https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/issues/93\#issuecomment-2042201321

src/module-folder-named-like-handler-bug.spec.ts

@@ -0,0 +1,30 @@
+import assert from 'node:assert/strict'
+import { it, describe } from 'node:test'
+import { ImportFromFolderNameError, packLambda } from './packLambda.js'
+import path, { dirname } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import fs from 'node:fs/promises'
+import os from 'node:os'
+
+const tmpDir = os.tmpdir()
+
+void describe('packLambda()', () => {
+	// See https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/issues/93#issuecomment-2042201321
+	void it('should fail if it imports from a folder that has the same name as the handler module', async () =>
+		assert.rejects(
+			async () =>
+				packLambda({
+					sourceFile: path.join(
+						dirname(fileURLToPath(import.meta.url)),
+						'test-data',
+						'module-folder-named-like-handler-bug',
+						'acme.ts',
+					),
+					zipFile: path.join(
+						await fs.mkdtemp(`${tmpDir}${path.sep}`),
+						'acme.zip',
+					),
+				}),
+			ImportFromFolderNameError,
+		))
+})

src/packLambda.ts

@@ -6,6 +6,7 @@ import { checkSumOfFiles } from './checksumOfFiles.js'
 import { commonParent } from './commonParent.js'
 import { findDependencies } from './findDependencies.js'
 import { fileURLToPath } from 'node:url'
+import path from 'node:path'
 
 export type PackedLambda = {
 	id: string
@@ -43,12 +44,21 @@ export const packLambda = async ({
 	debug?: (label: string, info: string) => void
 	progress?: (label: string, info: string) => void
 }): Promise<{ handler: string; hash: string }> => {
-	const lambdaFiles = [sourceFile, ...findDependencies(sourceFile)]
+	const deps = findDependencies(sourceFile)
+	const lambdaFiles = [sourceFile, ...deps]
 
 	const zipfile = new yazl.ZipFile()
 
 	const stripCommon = removeCommonAncestor(commonParent(lambdaFiles))
 
+	const handler = stripCommon(sourceFile)
+
+	const folderNames = new Set(deps.map(stripCommon).map((s) => s.split('/')[0]))
+	const handlerName = path.parse(handler).name
+	if (folderNames.has(handlerName)) {
+		throw new ImportFromFolderNameError(handlerName)
+	}
+
 	for (const file of lambdaFiles) {
 		const compiled = (
 			await swc.transformFile(file, {
@@ -91,3 +101,17 @@ export const packLambda = async ({
 
 	return { handler: stripCommon(sourceFile), hash }
 }
+
+/**
+ * @see https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/issues/93#issuecomment-2042201321
+ */
+export class ImportFromFolderNameError extends Error {
+	public readonly folderName: string
+	constructor(folderName: string) {
+		super(
+			`Import from folder with same name as handler ("${folderName}") not allowed!`,
+		)
+		this.name = 'ImportFromFolderNameError'
+		this.folderName = folderName
+	}
+}

src/test-data/module-folder-named-like-handler-bug/README.md

@@ -0,0 +1,7 @@
+Lambda's will fail if they import from a folder that has the same name as the
+handler.
+
+`packLambda` should fail in this case.
+
+See
+https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/issues/93#issuecomment-2042201321

src/test-data/module-folder-named-like-handler-bug/acme.ts

@@ -0,0 +1,3 @@
+import { hello } from './acme/lib.js'
+
+export const handler = (): string => hello()

src/test-data/module-folder-named-like-handler-bug/acme/lib.ts

@@ -0,0 +1 @@
+export const hello = (): string => 'Hello World!'