feat: add pure ESM support to esbuild and default bundlers

src/feature_flags.ts

@@ -3,9 +3,9 @@ import { env } from 'process'
 export const defaultFlags: Record<string, boolean> = {
   buildGoSource: Boolean(env.NETLIFY_EXPERIMENTAL_BUILD_GO_SOURCE),
   buildRustSource: Boolean(env.NETLIFY_EXPERIMENTAL_BUILD_RUST_SOURCE),
-  defaultEsModulesToEsbuild: Boolean(env.NETLIFY_EXPERIMENTAL_DEFAULT_ES_MODULES_TO_ESBUILD),
   parseWithEsbuild: false,
   traceWithNft: false,
+  zisi_detect_esm: false,
   zisi_pure_esm: false,
 }
 

src/runtimes/node/bundlers/esbuild/bundler.ts

@@ -4,11 +4,12 @@ import { build, Metafile } from '@netlify/esbuild'
 import { tmpName } from 'tmp-promise'
 
 import type { FunctionConfig } from '../../../../config.js'
+import { FeatureFlags } from '../../../../feature_flags.js'
 import { getPathWithExtension, safeUnlink } from '../../../../utils/fs.js'
 import type { RuntimeName } from '../../../runtime.js'
 import type { NodeBundlerName } from '../index.js'
 
-import { getBundlerTarget } from './bundler_target.js'
+import { getBundlerTarget, getModuleFormat } from './bundler_target.js'
 import { getDynamicImportsPlugin } from './plugin_dynamic_imports.js'
 import { getNativeModulesPlugin } from './plugin_native_modules.js'
 import { getNodeBuiltinPlugin } from './plugin_node_builtin.js'
@@ -28,6 +29,7 @@ export const bundleJsFile = async function ({
   basePath,
   config,
   externalModules = [],
+  featureFlags,
   ignoredModules = [],
   name,
   srcDir,
@@ -37,6 +39,7 @@ export const bundleJsFile = async function ({
   basePath?: string
   config: FunctionConfig
   externalModules: string[]
+  featureFlags: FeatureFlags
   ignoredModules: string[]
   name: string
   srcDir: string
@@ -84,11 +87,21 @@ export const bundleJsFile = async function ({
   // URLs, not paths, so even on Windows they should use forward slashes.
   const sourceRoot = targetDirectory.replace(/\\/g, '/')
 
+  // Configuring the output format of esbuild. The `includedFiles` array we get
+  // here contains additional paths to include with the bundle, like the path
+  // to a `package.json` with {"type": "module"} in case of an ESM function.
+  const { includedFiles: includedFilesFromModuleDetection, moduleFormat } = await getModuleFormat(
+    srcDir,
+    featureFlags,
+    config.nodeVersion,
+  )
+
   try {
     const { metafile = { inputs: {}, outputs: {} }, warnings } = await build({
       bundle: true,
       entryPoints: [srcFile],
       external,
+      format: moduleFormat,
       logLevel: 'warning',
       logLimit: ESBUILD_LOG_LIMIT,
       metafile: true,
@@ -108,12 +121,14 @@ export const bundleJsFile = async function ({
     })
     const inputs = Object.keys(metafile.inputs).map((path) => resolve(path))
     const cleanTempFiles = getCleanupFunction([...bundlePaths.keys()])
+    const additionalPaths = [...dynamicImportsIncludedPaths, ...includedFilesFromModuleDetection]
 
     return {
-      additionalPaths: [...dynamicImportsIncludedPaths],
+      additionalPaths,
       bundlePaths,
       cleanTempFiles,
       inputs,
+      moduleFormat,
       nativeNodeModules,
       nodeModulesWithDynamicImports: [...nodeModulesWithDynamicImports],
       warnings,

src/runtimes/node/bundlers/esbuild/bundler_target.ts

@@ -1,4 +1,7 @@
-const DEFAULT_VERSION = 'node12'
+import { FeatureFlags } from '../../../../feature_flags'
+import { ModuleFormat } from '../../utils/module_format'
+import { DEFAULT_NODE_VERSION, getNodeSupportMatrix } from '../../utils/node_version'
+import { getClosestPackageJson } from '../../utils/package_json'
 
 const versionMap = {
   '8.x': 'node8',
@@ -10,18 +13,41 @@ const versionMap = {
 type VersionKeys = keyof typeof versionMap
 type VersionValues = typeof versionMap[VersionKeys]
 
-export const getBundlerTarget = (suppliedVersion?: string): VersionValues => {
+const getBundlerTarget = (suppliedVersion?: string): VersionValues => {
   const version = normalizeVersion(suppliedVersion)
 
   if (version && version in versionMap) {
     return versionMap[version as VersionKeys]
   }
 
-  return DEFAULT_VERSION
+  return versionMap[`${DEFAULT_NODE_VERSION}.x`]
+}
+
+const getModuleFormat = async (
+  srcDir: string,
+  featureFlags: FeatureFlags,
+  configVersion?: string,
+): Promise<{ includedFiles: string[]; moduleFormat: ModuleFormat }> => {
+  const packageJsonFile = await getClosestPackageJson(srcDir)
+  const nodeSupport = getNodeSupportMatrix(configVersion)
+
+  if (featureFlags.zisi_pure_esm && packageJsonFile?.contents.type === 'module' && nodeSupport.esm) {
+    return {
+      includedFiles: [packageJsonFile.path],
+      moduleFormat: 'esm',
+    }
+  }
+
+  return {
+    includedFiles: [],
+    moduleFormat: 'cjs',
+  }
 }
 
 const normalizeVersion = (version?: string) => {
   const match = version && version.match(/^nodejs(.*)$/)
 
   return match ? match[1] : version
 }
+
+export { getBundlerTarget, getModuleFormat }

src/runtimes/node/bundlers/esbuild/index.ts

@@ -69,6 +69,7 @@ const bundle: BundleFunction = async ({
     bundlePaths,
     cleanTempFiles,
     inputs,
+    moduleFormat,
     nativeNodeModules = {},
     nodeModulesWithDynamicImports,
     warnings,
@@ -77,6 +78,7 @@ const bundle: BundleFunction = async ({
     basePath,
     config,
     externalModules,
+    featureFlags,
     ignoredModules,
     name,
     srcDir,
@@ -122,7 +124,7 @@ const bundle: BundleFunction = async ({
     bundlerWarnings,
     inputs,
     mainFile: normalizedMainFile,
-    moduleFormat: 'cjs',
+    moduleFormat,
     nativeNodeModules,
     nodeModulesWithDynamicImports,
     srcFiles: [...supportingSrcFiles, ...bundlePaths.keys()],

src/runtimes/node/bundlers/index.ts

@@ -101,21 +101,19 @@ export const getDefaultBundler = async ({
   mainFile: string
   featureFlags: FeatureFlags
 }): Promise<NodeBundlerName> => {
-  const { defaultEsModulesToEsbuild, traceWithNft } = featureFlags
-
   if (['.mjs', '.ts'].includes(extension)) {
     return 'esbuild'
   }
 
-  if (traceWithNft) {
+  if (featureFlags.traceWithNft) {
     return 'nft'
   }
 
-  if (defaultEsModulesToEsbuild) {
-    const isEsModule = await detectEsModule({ mainFile })
+  if (featureFlags.zisi_detect_esm) {
+    const functionIsESM = await detectEsModule({ mainFile })
 
-    if (isEsModule) {
-      return 'esbuild'
+    if (functionIsESM) {
+      return 'nft'
     }
   }
 

src/runtimes/node/utils/package_json.ts

@@ -1,5 +1,7 @@
 import { promises as fs } from 'fs'
+import { basename, join } from 'path'
 
+import findUp from 'find-up'
 import pkgDir from 'pkg-dir'
 
 export interface PackageJson {
@@ -16,18 +18,39 @@ export interface PackageJson {
   type?: string
 }
 
-const sanitiseFiles = (files: unknown): string[] | undefined => {
-  if (!Array.isArray(files)) {
-    return undefined
+export interface PackageJsonFile {
+  contents: PackageJson
+  path: string
+}
+
+export const getClosestPackageJson = async (resolveDir: string): Promise<PackageJsonFile | null> => {
+  const packageJsonPath = await findUp(
+    async (directory) => {
+      // We stop traversing if we're about to leave the boundaries of any
+      // node_modules directory.
+      if (basename(directory) === 'node_modules') {
+        return findUp.stop
+      }
+
+      const path = join(directory, 'package.json')
+      const hasPackageJson = await findUp.exists(path)
+
+      return hasPackageJson ? path : undefined
+    },
+    { cwd: resolveDir },
+  )
+
+  if (packageJsonPath === undefined) {
+    return null
   }
 
-  return files.filter((file) => typeof file === 'string')
-}
+  const packageJson = await readPackageJson(packageJsonPath)
 
-export const sanitisePackageJson = (packageJson: Record<string, unknown>): PackageJson => ({
-  ...packageJson,
-  files: sanitiseFiles(packageJson.files),
-})
+  return {
+    contents: packageJson,
+    path: packageJsonPath,
+  }
+}
 
 // Retrieve the `package.json` of a specific project or module
 export const getPackageJson = async function (srcDir: string): Promise<PackageJson> {
@@ -37,14 +60,7 @@ export const getPackageJson = async function (srcDir: string): Promise<PackageJs
     return {}
   }
 
-  const packageJsonPath = `${packageRoot}/package.json`
-  try {
-    // The path depends on the user's build, i.e. must be dynamic
-    const packageJson = JSON.parse(await fs.readFile(packageJsonPath, 'utf8'))
-    return sanitisePackageJson(packageJson)
-  } catch (error) {
-    throw new Error(`${packageJsonPath} is invalid JSON: ${error.message}`)
-  }
+  return readPackageJson(`${packageRoot}/package.json`)
 }
 
 export const getPackageJsonIfAvailable = async (srcDir: string): Promise<PackageJson> => {
@@ -56,3 +72,26 @@ export const getPackageJsonIfAvailable = async (srcDir: string): Promise<Package
     return {}
   }
 }
+
+const readPackageJson = async (path: string) => {
+  try {
+    // The path depends on the user's build, i.e. must be dynamic
+    const packageJson = JSON.parse(await fs.readFile(path, 'utf8'))
+    return sanitisePackageJson(packageJson)
+  } catch (error) {
+    throw new Error(`${path} is invalid JSON: ${error.message}`)
+  }
+}
+
+const sanitiseFiles = (files: unknown): string[] | undefined => {
+  if (!Array.isArray(files)) {
+    return undefined
+  }
+
+  return files.filter((file) => typeof file === 'string')
+}
+
+export const sanitisePackageJson = (packageJson: Record<string, unknown>): PackageJson => ({
+  ...packageJson,
+  files: sanitiseFiles(packageJson.files),
+})

tests/main.js

@@ -431,18 +431,18 @@ testMany(
 
 testMany(
   'Can bundle ESM functions and transpile them to CJS when the Node version is <14',
-  ['bundler_nft'],
+  ['bundler_default', 'bundler_esbuild', 'bundler_nft'],
   async (options, t) => {
     const length = 4
     const fixtureName = 'local-require-esm'
     const opts = merge(options, {
-      basePath: `${FIXTURES_DIR}/${fixtureName}`,
+      basePath: join(FIXTURES_DIR, fixtureName),
       config: {
         '*': {
           nodeVersion: 'nodejs12.x',
         },
       },
-      featureFlags: { defaultEsModulesToEsbuild: false },
+      featureFlags: { zisi_detect_esm: true, zisi_pure_esm: false },
     })
     const { files, tmpDir } = await zipFixture(t, fixtureName, {
       length,
@@ -485,19 +485,19 @@ testMany(
 
 testMany(
   'Can bundle ESM functions and transpile them to CJS when the Node version is <14 and `archiveType` is `none`',
-  ['bundler_esbuild', 'bundler_nft'],
+  ['bundler_default', 'bundler_esbuild', 'bundler_nft'],
   async (options, t) => {
     const length = 4
     const fixtureName = 'local-require-esm'
     const opts = merge(options, {
       archiveFormat: 'none',
-      basePath: `${FIXTURES_DIR}/${fixtureName}`,
+      basePath: join(FIXTURES_DIR, fixtureName),
       config: {
         '*': {
           nodeVersion: 'nodejs12.x',
         },
       },
-      featureFlags: { defaultEsModulesToEsbuild: false },
+      featureFlags: { zisi_detect_esm: true, zisi_pure_esm: false },
     })
     const { tmpDir } = await zipFixture(t, fixtureName, {
       length,
@@ -538,11 +538,14 @@ testMany(
 
 testMany(
   'Can bundle CJS functions that import ESM files with an `import()` expression',
-  ['bundler_esbuild', 'bundler_nft'],
+  ['bundler_default', 'bundler_esbuild', 'bundler_nft'],
   async (options, t) => {
     const fixtureName = 'node-cjs-importing-mjs'
+    const opts = merge(options, {
+      featureFlags: { zisi_detect_esm: true },
+    })
     const { files, tmpDir } = await zipFixture(t, fixtureName, {
-      opts: options,
+      opts,
     })
 
     await unzipFiles(files)
@@ -561,13 +564,13 @@ testMany(
 
 testMany(
   'Can bundle native ESM functions when the Node version is >=14 and the `zisi_pure_esm` flag is on',
-  ['bundler_nft'],
+  ['bundler_default', 'bundler_nft', 'bundler_esbuild'],
   async (options, t) => {
     const length = 2
     const fixtureName = 'node-esm'
     const opts = merge(options, {
-      basePath: `${FIXTURES_DIR}/${fixtureName}`,
-      featureFlags: { zisi_pure_esm: true },
+      basePath: join(FIXTURES_DIR, fixtureName),
+      featureFlags: { zisi_detect_esm: true, zisi_pure_esm: true },
     })
     const { files, tmpDir } = await zipFixture(t, fixtureName, {
       length,
@@ -593,12 +596,13 @@ testMany(
 
 testMany(
   'Can bundle ESM functions and transpile them to CJS when the Node version is >=14 and the `zisi_pure_esm` flag is off',
-  ['bundler_nft'],
+  ['bundler_default', 'bundler_esbuild', 'bundler_nft'],
   async (options, t) => {
     const length = 2
     const fixtureName = 'node-esm'
     const opts = merge(options, {
-      basePath: `${FIXTURES_DIR}/${fixtureName}`,
+      basePath: join(FIXTURES_DIR, fixtureName),
+      featureFlags: { zisi_detect_esm: true },
     })
     const { files, tmpDir } = await zipFixture(t, fixtureName, {
       length,