add Node.js v20 support

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [12.x, 14.x, 16.10.0, 16.16.0, 16.17.0, 16.x, 17.x, 18.5.0, 18.x]
+        node-version: [12.x, 14.x, 16.10.0, 16.16.0, 16.17.0, 16.x, 17.x, 18.5.0, 18.x, 20.x]
 
     steps:
       - uses: actions/checkout@v2
@@ -23,28 +23,12 @@ jobs:
       - run: npm run test:ts
         if: (matrix.node-version != '12.x' && matrix.node-version != '14.x' && matrix.node-version != '16.10.0')
 
-  build-unsupported:
-    runs-on: ubuntu-latest
-
-    strategy:
-      matrix:
-        node-version: [20.x]
-
-    steps:
-      - uses: actions/checkout@v2
-      - name: Use Node.js ${{ matrix.node-version }}
-        uses: actions/setup-node@v2
-        with:
-          node-version: ${{ matrix.node-version }}
-      - run: npm install
-      - run: npm test:unsupported
-
   build-win:
       runs-on: windows-latest
 
       strategy:
         matrix:
-          node-version: [ 12.x, 14.x, 16.10.0, 16.16.0, 16.17.0, 16.x, 18.5.0, 18.x ]
+          node-version: [12.x, 14.x, 16.10.0, 16.16.0, 16.17.0, 16.x, 18.5.0, 18.x, 20.x]
 
       steps:
         - uses: actions/checkout@v2

hook.js

@@ -14,6 +14,12 @@ const NODE_MINOR = Number(NODE_VERSION[1])
 
 let entrypoint
 
+if (NODE_MAJOR >= 20) {
+  getExports = require('./lib/get-exports.js')
+} else {
+  getExports = (url) => import(url).then(Object.keys)
+}
+
 function hasIitm (url) {
   try {
     return new URL(url).searchParams.has('iitm')
@@ -103,16 +109,16 @@ function createHook (meta) {
 
     return {
       url: addIitm(url.url),
-      shortCircuit: true
+      shortCircuit: true,
+      format: url.format
     }
   }
 
   const iitmURL = new URL('lib/register.js', meta.url).toString()
   async function getSource (url, context, parentGetSource) {
     if (hasIitm(url)) {
       const realUrl = deleteIitm(url)
-      const realModule = await import(realUrl)
-      const exportNames = Object.keys(realModule)
+      const exportNames = await getExports(realUrl, context, parentGetSource)
       return {
         source: `
 import { register } from '${iitmURL}'
@@ -137,7 +143,7 @@ register('${realUrl}', namespace, set, '${specifiers.get(realUrl)}')
   // For Node.js 16.12.0 and higher.
   async function load (url, context, parentLoad) {
     if (hasIitm(url)) {
-      const { source } = await getSource(url, context)
+      const { source } = await getSource(url, context, parentLoad)
       return {
         source,
         shortCircuit: true,
@@ -148,10 +154,7 @@ register('${realUrl}', namespace, set, '${specifiers.get(realUrl)}')
     return parentLoad(url, context, parentLoad)
   }
 
-  if (NODE_MAJOR >= 20) {
-    process.emitWarning('import-in-the-middle is currently unsupported on Node.js v20 and has been disabled.')
-    return {} // TODO: Add support for Node >=20
-  } else if (NODE_MAJOR >= 17 || (NODE_MAJOR === 16 && NODE_MINOR >= 12)) {
+  if (NODE_MAJOR >= 17 || (NODE_MAJOR === 16 && NODE_MINOR >= 12)) {
     return { load, resolve }
   } else {
     return {

lib/get-esm-exports.js

@@ -0,0 +1,97 @@
+'use strict'
+
+const { Parser } = require('acorn')
+const { importAssertions } = require('acorn-import-assertions');
+
+const acornOpts = {
+  ecmaVersion: 'latest',
+  sourceType: 'module'
+}
+
+const parser = Parser.extend(importAssertions)
+
+function warn (txt) {
+  process.emitWarning(txt, 'get-esm-exports')
+}
+
+function getEsmExports (moduleStr) {
+  const exportedNames = new Set()
+  const tree = parser.parse(moduleStr, acornOpts)
+  for (const node of tree.body) {
+    if (!node.type.startsWith('Export')) continue
+    switch (node.type) {
+      case 'ExportNamedDeclaration':
+        if (node.declaration) {
+          parseDeclaration(node, exportedNames)
+        } else {
+          parseSpecifiers(node, exportedNames)
+        }
+        break
+      case 'ExportDefaultDeclaration':
+        exportedNames.add('default')
+        break
+      case 'ExportAllDeclaration':
+        if (node.exported) {
+          exportedNames.add(node.exported.name)
+        } else {
+          exportedNames.add('*')
+        }
+        break
+      default:
+        warn('unrecognized export type: ' + node.type)
+    }
+  }
+  return Array.from(exportedNames)
+}
+
+function parseDeclaration (node, exportedNames) {
+  switch (node.declaration.type) {
+    case 'FunctionDeclaration':
+      exportedNames.add(node.declaration.id.name)
+      break
+    case 'VariableDeclaration':
+      for (const varDecl of node.declaration.declarations) {
+        parseVariableDeclaration(varDecl, exportedNames)
+      }
+      break
+    case 'ClassDeclaration':
+      exportedNames.add(node.declaration.id.name)
+      break
+    default:
+      warn('unknown declaration type: ' + node.delcaration.type)
+  }
+}
+
+function parseVariableDeclaration (node, exportedNames) {
+  switch (node.id.type) {
+    case 'Identifier':
+      exportedNames.add(node.id.name)
+      break
+    case 'ObjectPattern':
+      for (const prop of node.id.properties) {
+        exportedNames.add(prop.value.name)
+      }
+      break
+    case 'ArrayPattern':
+      for (const elem of node.id.elements) {
+        exportedNames.add(elem.name)
+      }
+      break
+    default:
+      warn('unknown variable declaration type: ' + node.id.type)
+  }
+}
+
+function parseSpecifiers (node, exportedNames) {
+  for (const specifier of node.specifiers) {
+    if (specifier.exported.type === 'Identifier') {
+      exportedNames.add(specifier.exported.name)
+    } else if (specifier.exported.type === 'Literal') {
+      exportedNames.add(specifier.exported.value)
+    } else {
+      warn('unrecognized specifier type: ' + specifier.exported.type)
+    }
+  }
+}
+
+module.exports = getEsmExports

lib/get-exports.js

@@ -0,0 +1,51 @@
+'use strict'
+
+const getEsmExports = require('./get-esm-exports.js')
+const { parse: getCjsExports } = require('cjs-module-lexer')
+const fs = require('fs')
+const { fileURLToPath } = require('url')
+
+function addDefault(arr) {
+  return Array.from(new Set(['default', ...arr]))
+}
+
+async function getExports (url, context, parentLoad) {
+  // `parentLoad` gives us the possibility of getting the source
+  // from an upstream loader. This doesn't always work though,
+  // so later on we fall back to reading it from disk.
+  const parentCtx = await parentLoad(url, context)
+  let source = parentCtx.source
+  const format = parentCtx.format
+
+  // TODO support non-node/file urls somehow?
+  if (format === 'builtin') {
+    // Builtins don't give us the source property, so we're stuck
+    // just requiring it to get the exports.
+    return addDefault(Object.keys(require(url)))
+  }
+
+  if (!source) {
+    // Sometimes source is retrieved by parentLoad, sometimes it isn't.
+    source = fs.readFileSync(fileURLToPath(url), 'utf8')
+  }
+
+  if (format === 'module') {
+    return getEsmExports(source)
+  }
+  if (format === 'commonjs') {
+    return addDefault(getCjsExports(source).exports)
+  }
+
+  // At this point our `format` is either undefined or not known by us. Fall
+  // back to parsing as ESM/CJS.
+  const esmExports = getEsmExports(source)
+  if (!esmExports.length) {
+    // TODO(bengl) it's might be possible to get here if somehow the format
+    // isn't set at first and yet we have an ESM module with no exports.
+    // I couldn't construct an example that would do this, so maybe it's
+    // impossible?
+    return addDefault(getCjsExports(source).exports)
+  }
+}
+
+module.exports = getExports

package.json

@@ -4,12 +4,11 @@
   "description": "Intercept imports in Node.js",
   "main": "index.js",
   "scripts": {
-    "test": "c8 --check-coverage --lines 85 imhotap --runner test/runtest --files test/{hook,low-level,other}/*",
-    "test:unsupported": "imhotap --runner test/runtest --files test/hook/loader.mjs",
-    "test-win": "c8 --check-coverage --lines 85 imhotap --runner test\\runtest.bat --files test/{hook,low-level,other}/*",
+    "test": "c8 --check-coverage --lines 85 imhotap --runner test/runtest --files test/{hook,low-level,other,get-esm-exports}/*",
+    "test-win": "c8 --check-coverage --lines 85 imhotap --runner test\\runtest.bat --files test/{hook,low-level,other,get-esm-exports}/*",
     "test:ts": "c8 imhotap --runner test/runtest --files test/typescript/*.test.mts",
     "test-win:ts": "c8 imhotap --runner test\\runtest.bat --files test/typescript/*.test.mts",
-    "coverage": "c8 --reporter html imhotap --runner test/runtest --files test/{hook,low-level,other}/* && echo '\nNow open coverage/index.html\n'"
+    "coverage": "c8 --reporter html imhotap --runner test/runtest --files test/{hook,low-level,other,get-esm-exports}/* && echo '\nNow open coverage/index.html\n'"
   },
   "repository": {
     "type": "git",
@@ -37,6 +36,9 @@
     "typescript": "^4.7.4"
   },
   "dependencies": {
+    "acorn": "^8.8.2",
+    "acorn-import-assertions": "^1.9.0",
+    "cjs-module-lexer": "^1.2.2",
     "module-details-from-path": "^1.0.3"
   }
 }

test/fixtures/esm-exports.txt

@@ -0,0 +1,32 @@
+// Exporting declarations
+export let name1, name2/*, … */; // also var //| name1,name2
+export const name1 = 1, name2 = 2/*, … */; // also var, let //| name1,name2
+export function functionName() { /* … */ } //| functionName
+export class ClassName { /* … */ } //| ClassName
+export function* generatorFunctionName() { /* … */ } //| generatorFunctionName
+export const { name1, name2: bar } = o; //| name1,bar
+export const [ name1, name2 ] = array; //| name1,name2
+
+// Export list
+let name1, nameN; export { name1, /* …, */ nameN }; //| name1,nameN
+let variable1, variable2, nameN; export { variable1 as name1, variable2 as name2, /* …, */ nameN }; //| name1,name2,nameN
+let variable1; export { variable1 as "string name" }; //| string name
+let name1; export { name1 as default /*, … */ }; //| default
+
+// Default exports
+export default expression; //| default
+export default function functionName() { /* … */ } //| default
+export default class ClassName { /* … */ } //| default
+export default function* generatorFunctionName() { /* … */ } //| default
+export default function () { /* … */ } //| default
+export default class { /* … */ } //| default
+export default function* () { /* … */ } //| default
+
+// Aggregating modules
+export * from "module-name"; //| *
+export * as name1 from "module-name"; //| name1
+export { name1, /* …, */ nameN } from "module-name"; //| name1,nameN
+export { import1 as name1, import2 as name2, /* …, */ nameN } from "module-name"; //| name1,name2,nameN
+export { default, /* …, */ } from "module-name"; //| default
+export { default as name1 } from "module-name"; //| name1
+

test/get-esm-exports/v20-get-esm-exports.js

@@ -0,0 +1,31 @@
+'use strict'
+
+const getEsmExports = require('../../lib/get-esm-exports.js')
+const fs = require('fs')
+const assert = require('assert')
+const path = require('path')
+
+const fixturePath = path.join(__dirname, '../fixtures/esm-exports.txt')
+const fixture = fs.readFileSync(fixturePath, 'utf8')
+
+fixture.split('\n').forEach(line => {
+  if (!line.includes(' //| ')) return
+  const [mod, testStr] = line.split(' //| ')
+  const expectedNames = testStr.split(',').map(x => x.trim())
+  if (expectedNames[0] === '') {
+    expectedNames.length = 0
+  }
+  const names = getEsmExports(mod)
+  assert.deepEqual(expectedNames, names)
+  console.log(`${mod}\n  ✅ contains exports: ${testStr}`)
+})
+
+// // Generate fixture data
+// fixture.split('\n').forEach(line => {
+//   if (!line.includes('export ')) {
+//     console.log(line)
+//     return
+//   }
+//   const names = getEsmExports(line)
+//   console.log(line, '//|', names.join(','))
+// })