fix: CommonJs bare specifier resolution (#96)

Closes #95

I've also made the `getExports` functions return `Set<string>` instead
of `string[]` as this saves a load of unnecessary allocations.

I've also run this through the additional module tests in #93 and get
the same results.

lib/get-esm-exports.js

@@ -29,7 +29,7 @@ function warn (txt) {
  * @param {string} params.moduleSource The source code of the module to parse
  * and interpret.
  *
- * @returns {string[]} The identifiers exported by the module along with any
+ * @returns {Set<string>} The identifiers exported by the module along with any
  * custom directives.
  */
 function getEsmExports (moduleSource) {
@@ -62,7 +62,7 @@ function getEsmExports (moduleSource) {
  warn('unrecognized export type: ' + node.type)
  }
  }
- return Array.from(exportedNames)
+ return exportedNames
 }
 
 function parseDeclaration (node, exportedNames) {

lib/get-exports.js

@@ -1,36 +1,60 @@
 'use strict'
 
 const getEsmExports = require('./get-esm-exports.js')
-const { parse: getCjsExports } = require('cjs-module-lexer')
-const fs = require('fs')
+const { parse: parseCjs } = require('cjs-module-lexer')
+const { readFileSync } = require('fs')
+const { builtinModules } = require('module')
 const { fileURLToPath, pathToFileURL } = require('url')
+const { dirname } = require('path')
 
 function addDefault (arr) {
- return Array.from(new Set(['default', ...arr]))
+ return new Set(['default', ...arr])
+}
+
+// Cached exports for Node built-in modules
+const BUILT_INS = new Map()
+
+function getExportsForNodeBuiltIn (name) {
+ let exports = BUILT_INS.get()
+
+ if (!exports) {
+ exports = new Set(addDefault(Object.keys(require(name))))
+ BUILT_INS.set(name, exports)
+ }
+
+ return exports
 }
 
 const urlsBeingProcessed = new Set() // Guard against circular imports.
 
-async function getFullCjsExports (url, context, parentLoad, source) {
+async function getCjsExports (url, context, parentLoad, source) {
  if (urlsBeingProcessed.has(url)) {
  return []
  }
  urlsBeingProcessed.add(url)
 
- const ex = getCjsExports(source)
- const full = Array.from(new Set([
- ...addDefault(ex.exports),
- ...(await Promise.all(ex.reexports.map(re => getExports(
- (/^(..?($|\/|\\))/).test(re)
- ? pathToFileURL(require.resolve(fileURLToPath(new URL(re, url)))).toString()
- : pathToFileURL(require.resolve(re)).toString(),
- context,
- parentLoad
- )))).flat()
- ]))
-
- urlsBeingProcessed.delete(url)
- return full
+ try {
+ const result = parseCjs(source)
+ const full = addDefault(result.exports)
+
+ await Promise.all(result.reexports.map(async re => {
+ if (re.startsWith('node:') || builtinModules.includes(re)) {
+ for (const each of getExportsForNodeBuiltIn(re)) {
+ full.add(each)
+ }
+ } else {
+ // Resolve the re-exported module relative to the current module.
+ const newUrl = pathToFileURL(require.resolve(re, { paths: [dirname(fileURLToPath(url))] })).href
+ for (const each of await getExports(newUrl, context, parentLoad)) {
+ full.add(each)
+ }
+ }
+ }))
+
+ return full
+ } finally {
+ urlsBeingProcessed.delete(url)
+ }
 }
 
 /**
@@ -45,7 +69,7 @@ async function getFullCjsExports (url, context, parentLoad, source) {
  * @param {Function} parentLoad Next hook function in the loaders API
  * hook chain.
  *
- * @returns {Promise<string[]>} An array of identifiers exported by the module.
+ * @returns {Promise<Set<string>>} An array of identifiers exported by the module.
  * Please see {@link getEsmExports} for caveats on special identifiers that may
  * be included in the result set.
  */
@@ -57,23 +81,23 @@ async function getExports (url, context, parentLoad) {
  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 === 'builtin') {
+ // Builtins don't give us the source property, so we're stuck
+ // just requiring it to get the exports.
+ return getExportsForNodeBuiltIn(url)
+ }
+
+ // Sometimes source is retrieved by parentLoad, CommonJs isn't.
+ source = readFileSync(fileURLToPath(url), 'utf8')
  }
 
  if (format === 'module') {
  return getEsmExports(source)
  }
+
  if (format === 'commonjs') {
- return getFullCjsExports(url, context, parentLoad, source)
+ return getCjsExports(url, context, parentLoad, source)
  }
 
  // At this point our `format` is either undefined or not known by us. Fall
@@ -84,7 +108,7 @@ async function getExports (url, context, parentLoad) {
  // 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 getFullCjsExports(url, context, parentLoad, source)
+ return getCjsExports(url, context, parentLoad, source)
  }
 }
 

test/fixtures/re-export-cjs-built-in.js

@@ -0,0 +1 @@
+module.exports = require('util').deprecate

test/fixtures/re-export-cjs.js

@@ -0,0 +1 @@
+module.exports = require('some-external-cjs-module').foo

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

@@ -15,7 +15,7 @@ fixture.split('\n').forEach(line => {
  if (expectedNames[0] === '') {
  expectedNames.length = 0
  }
- const names = getEsmExports(mod)
+ const names = Array.from(getEsmExports(mod))
  assert.deepEqual(expectedNames, names)
  console.log(`${mod}\n ✅ contains exports: ${testStr}`)
 })

test/hook/re-export-cjs.mjs

@@ -0,0 +1,19 @@
+import Hook from '../../index.js'
+import foo from '../fixtures/re-export-cjs-built-in.js'
+import foo2 from '../fixtures/re-export-cjs.js'
+import { strictEqual } from 'assert'
+
+Hook((exports, name) => {
+ if (name.endsWith('fixtures/re-export-cjs-built-in.js')) {
+ strictEqual(typeof exports.default, 'function')
+ exports.default = '1'
+ }
+
+ if (name.endsWith('fixtures/re-export-cjs.js')) {
+ strictEqual(exports.default, 'bar')
+ exports.default = '2'
+ }
+})
+
+strictEqual(foo, '1')
+strictEqual(foo2, '2')