feat: correct module systems by file extension. addresses microsoft/TypeScript#51990, microsoft/TypeScript#27957,

microsoft/TypeScript#50985

Author: knightedcodemonkey

README.md

@@ -6,7 +6,7 @@
 
 Node.js tool for creating a TypeScript dual package.
 
-Early stages of development. Inspired by https://github.com/microsoft/TypeScript/issues/49462.
+Inspired by https://github.com/microsoft/TypeScript/issues/49462.
 
 ## Requirements
 
@@ -79,8 +79,8 @@ Options:
 
 ## Gotchas
 
-* Unfortunately, TypeScript doesn't really build [dual packages](https://nodejs.org/api/packages.html#dual-commonjses-module-packages) very well in regards to preserving module system by file extension. For instance, it will **always** create CJS exports when `--module commonjs` is used, _even on files with an `.mts` extension_, which is contrary to [how Node determines module systems](https://nodejs.org/api/packages.html#determining-module-system). The `tsc` compiler is fundamentally broken in this regard. One reference issue is https://github.com/microsoft/TypeScript/issues/54573. If you use `.mts` extensions to enforce an ESM module system, this will break in the corresponding dual CJS build. There is no way to fix this until TypeScript fixes their compiler.
+These are definitely edge cases, and would only really come up if your project mixes file extensions. For example, if you have `.ts` files combined with `.mts`, and/or `.cts`. For most project, things should just work as expected.
 
-* If targeting a dual CJS build, and you are using [top level `await`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await#top_level_await), you will most likely encounter the compilation error `error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'es2022', 'esnext', 'system', 'node16', or 'nodenext', and the 'target' option is set to 'es2017' or higher.` during the CJS build. This is because `duel` creates a temporary `tsconfig.json` from your original and necessarily overwrites the `--module` and `--moduleResolution` based on the provided `--target-ext`. There is no workaround other than to **not** use top level await if you want a dual build.
+* Unfortunately, TypeScript doesn't really build [dual packages](https://nodejs.org/api/packages.html#dual-commonjses-module-packages) very well in regards to preserving module system by file extension. For instance, there doesn't appear to be a way to convert an arbitrary `.ts` file into another module system, _while also preserving the module system of `.mts` and `.cts` files_. In my opinion, the `tsc` compiler is fundamentally broken in this regard, and at best is enforcing usage patterns it shouldn't. If you want to see one of my extended rants on this, check out this [comment](https://github.com/microsoft/TypeScript/pull/50985#issuecomment-1656991606). This is only mentioned for transparency, `duel` will correct for this and produce files with the module system you would expect based on the files extension, so that it works with [how Node.js determines module systems](https://nodejs.org/api/packages.html#determining-module-system).
 
 * If doing an `import type` across module systems, i.e. from `.mts` into `.cts`, or vice versa, you might encounter the compilation error ``error TS1452: 'resolution-mode' assertions are only supported when `moduleResolution` is `node16` or `nodenext`.``. This is a [known issue](https://github.com/microsoft/TypeScript/issues/49055) and TypeScript currently suggests installing the nightly build, i.e. `npm i typescript@next`.

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "@knighted/duel",
-  "version": "1.0.0-alpha.3",
+  "version": "1.0.0-alpha.4",
   "description": "TypeScript dual packages.",
   "type": "module",
   "main": "dist",
@@ -44,7 +44,7 @@
     "url": "https://github.com/knightedcodemonkey/duel/issues"
   },
   "peerDependencies": {
-    "typescript": "^5.0.0"
+    "typescript": ">=4.0.0"
   },
   "devDependencies": {
     "babel-dual-package": "^1.0.0-rc.5",

package.json

@@ -1,9 +1,9 @@
 #!/usr/bin/env node
 
 import { argv, cwd } from 'node:process'
-import { join } from 'node:path'
+import { join, relative } from 'node:path'
 import { spawnSync } from 'node:child_process'
-import { writeFile, rm } from 'node:fs/promises'
+import { writeFile, copyFile, rm } from 'node:fs/promises'
 import { randomBytes } from 'node:crypto'
 import { performance } from 'node:perf_hooks'
 
@@ -13,7 +13,6 @@ import { specifier } from '@knighted/specifier'
 import { init } from './init.js'
 import { getRealPathAsFileUrl, logError, log } from './util.js'
 
-// TypeScript is defined as a peer dependency.
 const tsc = join(cwd(), 'node_modules', '.bin', 'tsc')
 const runBuild = project => {
   const { status, error } = spawnSync(tsc, ['-p', project], { stdio: 'inherit' })
@@ -42,7 +41,7 @@ const duel = async args => {
   const ctx = await init(args)
 
   if (ctx) {
-    const { projectDir, tsconfig, targetExt, configPath } = ctx
+    const { projectDir, tsconfig, targetExt, configPath, absoluteOutDir } = ctx
     const startTime = performance.now()
 
     log('Starting primary build...\n')
@@ -55,13 +54,15 @@ const duel = async args => {
       const { outDir } = tsconfig.compilerOptions
       const dualConfigPath = join(projectDir, `tsconfig.${hex}.json`)
       const dualOutDir = isCjsBuild ? join(outDir, 'cjs') : join(outDir, 'mjs')
+      // Using structuredClone() would require node >= 17.0.0
       const tsconfigDual = {
         ...tsconfig,
         compilerOptions: {
           ...tsconfig.compilerOptions,
           outDir: dualOutDir,
-          module: isCjsBuild ? 'CommonJS' : 'NodeNext',
-          moduleResolution: isCjsBuild ? 'Node' : 'NodeNext',
+          module: isCjsBuild ? 'CommonJS' : 'ESNext',
+          // Best way to make this work given how tsc works
+          moduleResolution: 'Node',
         },
       }
 
@@ -71,7 +72,8 @@ const duel = async args => {
       await rm(dualConfigPath, { force: true })
 
       if (success) {
-        const filenames = await glob(`${join(projectDir, dualOutDir)}/**/*{.js,.d.ts}`, {
+        const absoluteDualOutDir = join(projectDir, dualOutDir)
+        const filenames = await glob(`${absoluteDualOutDir}/**/*{.js,.d.ts}`, {
           ignore: 'node_modules/**',
         })
 
@@ -95,6 +97,55 @@ const duel = async args => {
           await rm(filename, { force: true })
         }
 
+        /**
+         * This is a fix for tsc compiler which doesn't seem to support
+         * converting an arbitrary `.ts` file, into another module system,
+         * while also preserving the module systems of `.mts` and `.cts` files.
+         *
+         * Hopefully it can be removed when TS updates their supported options,
+         * or at least how the combination of `--module` and `--moduleResolution`
+         * currently work.
+         *
+         * @see https://github.com/microsoft/TypeScript/pull/50985#issuecomment-1656991606
+         */
+        if (isCjsBuild) {
+          const mjsFiles = await glob(`${absoluteOutDir}/**/*.mjs`, {
+            ignore: ['node_modules/**', `${absoluteDualOutDir}/**`],
+          })
+
+          for (const filename of mjsFiles) {
+            const relativeFn = relative(absoluteOutDir, filename)
+
+            await copyFile(filename, join(absoluteDualOutDir, relativeFn))
+          }
+        } else {
+          const cjsFiles = await glob(`${absoluteOutDir}/**/*.cjs`, {
+            ignore: ['node_modules/**', `${absoluteDualOutDir}/**`],
+          })
+
+          for (const filename of cjsFiles) {
+            const relativeFn = relative(absoluteOutDir, filename)
+
+            await copyFile(filename, join(absoluteDualOutDir, relativeFn))
+          }
+
+          /**
+           * Now copy the good .mjs files from the dual out dir
+           * to the original out dir, but build the file path
+           * from the original out dir to distinguish from the
+           * dual build .mjs files.
+           */
+          const mjsFiles = await glob(`${absoluteOutDir}/**/*.mjs`, {
+            ignore: ['node_modules/**', `${absoluteDualOutDir}/**`],
+          })
+
+          for (const filename of mjsFiles) {
+            const relativeFn = relative(absoluteOutDir, filename)
+
+            await copyFile(join(absoluteDualOutDir, relativeFn), filename)
+          }
+        }
+
         log(
           `Successfully created a dual ${targetExt
             .replace('.', '')

src/duel.js

@@ -0,0 +1,18 @@
+{
+  "version": "0.0.0",
+  "type": "commonjs",
+  "exports": {
+    ".": {
+      "import": {
+        "types": "./dist/mjs/index.d.mts",
+        "default": "./dist/index.mjs"
+      },
+      "require": {
+        "types": "./dist/index.d.cts",
+        "default": "./dist/index.cjs"
+      },
+      "default": "./dist/index.cjs"
+    },
+    "./package.json": "./package.json"
+  }
+}

test/__fixtures__/cjsProject/package.json

@@ -0,0 +1,9 @@
+interface ESM {
+  esm: boolean;
+}
+
+export const esm: ESM = {
+  esm: true
+}
+
+export type { ESM }

test/__fixtures__/project/src/cjs.cts renamed to test/__fixtures__/cjsProject/src/cjs.cts

@@ -16,5 +16,5 @@ const mod: Mod = {
   }
 }
 
-export { mod }
+export { mod, cjs }
 export type { Mod }

test/__fixtures__/project/src/esm.mts renamed to test/__fixtures__/cjsProject/src/esm.mts

@@ -0,0 +1,39 @@
+import { mod } from "./folder/module.js"
+import { cjs } from './cjs.cjs'
+
+import type { Mod } from "./folder/module.js"
+import type { CJS } from "./cjs.cjs"
+
+interface User {
+  name: string;
+  id: number;
+  mod: Mod;
+  esm: any;
+  cjs: CJS;
+}
+
+class UserAccount {
+  name: string;
+  id: number;
+  mod: Mod;
+  esm: any;
+  cjs: CJS;
+
+  constructor(name: string, id: number, mod: Mod, esm: any, cjs: CJS) {
+    this.name = name;
+    this.id = id;
+    this.mod = mod;
+    this.esm = esm;
+    this.cjs = cjs;
+  }
+}
+
+const getUser = async () => {
+  const { esm } = await import('./esm.mjs')
+
+  return new UserAccount("Murphy", 1, mod, esm, cjs)
+}
+
+export type { User }
+
+export { getUser }

test/__fixtures__/cjsProject/src/folder/another.mts

@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "target": "ESNext",
+    "module": "CommonJS",
+    "moduleResolution": "Node",
+    "declaration": true,
+    "strict": false,
+    "outDir": "dist",
+    "lib": ["ES2015"]
+  },
+  "include": ["src"]
+}

test/__fixtures__/project/src/folder/module.ts renamed to test/__fixtures__/cjsProject/src/folder/module.ts

@@ -0,0 +1,3 @@
+//import * as cjs from './dist/cjs/cjs.cjs'
+
+require('./dist/cjs/cjs.cjs')

test/__fixtures__/cjsProject/src/index.ts

@@ -0,0 +1,39 @@
+/*
+import type { ESM } from './esm.mjs' assert { 'resolution-mode': 'import' };
+
+interface CJS {
+  cjs: boolean,
+  esm: ESM;
+}
+
+const func = async () => {
+  const { esm } = await import('./esm.mjs')
+
+  const cjs: CJS = {
+    cjs: true,
+    esm
+  }
+
+  return cjs
+}
+
+export { func }
+
+export type { CJS }
+*/
+
+import MagicString from "magic-string"
+
+interface CJS {
+  cjs: boolean;
+  magic: MagicString;
+}
+
+const cjs: CJS = {
+  cjs: true,
+  magic: new MagicString('magic')
+}
+
+export { cjs }
+
+export type { CJS }

test/__fixtures__/cjsProject/tsconfig.json

@@ -0,0 +1,9 @@
+interface ESM {
+  esm: boolean;
+}
+
+export const esm: ESM = {
+  esm: true
+}
+
+export type { ESM }

test/__fixtures__/project/package.json renamed to test/__fixtures__/esmProject/package.json

@@ -0,0 +1,9 @@
+interface ESM {
+  esm: boolean;
+}
+
+export const esm: ESM = {
+  esm: true
+}
+
+export type { ESM }

test/__fixtures__/esmProject/script.js

@@ -0,0 +1,20 @@
+import MagicString from "magic-string";
+import { cjs } from "../cjs.cjs";
+
+import type { CJS } from "../cjs.cjs";
+
+interface Mod {
+  prop: string;
+  cjs: CJS
+}
+
+const mod: Mod = {
+  prop: 'foobar',
+  cjs: {
+    cjs: true,
+    magic: new MagicString('module')
+  }
+}
+
+export { mod, cjs }
+export type { Mod }

test/__fixtures__/esmProject/src/cjs.cts

@@ -8,5 +8,5 @@
     "outDir": "dist",
     "lib": ["ES2015"]
   },
-  "include": ["src/*.ts"]
+  "include": ["src"]
 }