From 119ddf11f3df55223d39bbe6867e760eaee788a8 Mon Sep 17 00:00:00 2001
From: Jacob Smith <3012099+JakobJingleheimer@users.noreply.github.com>
Date: Thu, 25 Aug 2022 16:47:24 +0200
Subject: [PATCH 1/3] Add loader to support mixed-format packages

---
 mixed-format/fixture/cjs.js       |  1 +
 mixed-format/fixture/esm.js       |  1 +
 mixed-format/fixture/package.json |  3 +++
 mixed-format/loader.mjs           | 23 +++++++++++++++++++++++
 mixed-format/test.mjs             |  8 ++++++++
 5 files changed, 36 insertions(+)
 create mode 100644 mixed-format/fixture/cjs.js
 create mode 100644 mixed-format/fixture/esm.js
 create mode 100644 mixed-format/fixture/package.json
 create mode 100644 mixed-format/loader.mjs
 create mode 100644 mixed-format/test.mjs

diff --git a/mixed-format/fixture/cjs.js b/mixed-format/fixture/cjs.js
new file mode 100644
index 0000000..deb8531
--- /dev/null
+++ b/mixed-format/fixture/cjs.js
@@ -0,0 +1 @@
+exports.qux = 'zed';
diff --git a/mixed-format/fixture/esm.js b/mixed-format/fixture/esm.js
new file mode 100644
index 0000000..c155820
--- /dev/null
+++ b/mixed-format/fixture/esm.js
@@ -0,0 +1 @@
+export const foo = 'bar';
diff --git a/mixed-format/fixture/package.json b/mixed-format/fixture/package.json
new file mode 100644
index 0000000..a0df0c8
--- /dev/null
+++ b/mixed-format/fixture/package.json
@@ -0,0 +1,3 @@
+{
+	"type": "commonjs"
+}
diff --git a/mixed-format/loader.mjs b/mixed-format/loader.mjs
new file mode 100644
index 0000000..aa38eaa
--- /dev/null
+++ b/mixed-format/loader.mjs
@@ -0,0 +1,23 @@
+export async function load(url, context, nextLoad) {
+  if (!url.endsWith('.js')) return nextLoad(url);
+
+  const nextResult = await nextLoad(url, { ...context, format: 'module' })
+    .then((result) => {
+      if (`${result.source}`.match(/exports[\. =]/)) throw new Error('Module is commonjs');
+
+      return result;
+    })
+    .catch(async (err) => {
+      if (
+        (err?.message.includes('require') && err.includes('import'))
+        || err?.message.includes('commonjs')
+      ) return {
+        format: 'commonjs',
+        source: (await nextLoad(url, {...context, format: 'commonjs' })).source,
+      };
+
+      throw err;
+    });
+
+  return nextResult;
+}
diff --git a/mixed-format/test.mjs b/mixed-format/test.mjs
new file mode 100644
index 0000000..616dc86
--- /dev/null
+++ b/mixed-format/test.mjs
@@ -0,0 +1,8 @@
+import assert from 'node:assert';
+
+import { foo } from './fixture/esm.js';
+import { qux } from './fixture/cjs.js';
+
+
+assert.strictEqual(foo, 'bar');
+assert.strictEqual(qux, 'zed');

From ec656c6afca583cdac69f6d0951b8073d339137f Mon Sep 17 00:00:00 2001
From: Jacob Smith <3012099+JakobJingleheimer@users.noreply.github.com>
Date: Thu, 25 Aug 2022 17:57:12 +0200
Subject: [PATCH 2/3] add nested cjs via require

---
 mixed-format/fixture/cjs.js  |  2 +-
 mixed-format/fixture/cjs2.js |  1 +
 mixed-format/loader.mjs      | 22 ++++++++++++++++------
 3 files changed, 18 insertions(+), 7 deletions(-)
 create mode 100644 mixed-format/fixture/cjs2.js

diff --git a/mixed-format/fixture/cjs.js b/mixed-format/fixture/cjs.js
index deb8531..b7d3583 100644
--- a/mixed-format/fixture/cjs.js
+++ b/mixed-format/fixture/cjs.js
@@ -1 +1 @@
-exports.qux = 'zed';
+exports.qux = require('./cjs2.js');
diff --git a/mixed-format/fixture/cjs2.js b/mixed-format/fixture/cjs2.js
new file mode 100644
index 0000000..732f419
--- /dev/null
+++ b/mixed-format/fixture/cjs2.js
@@ -0,0 +1 @@
+module.exports = 'zed';
diff --git a/mixed-format/loader.mjs b/mixed-format/loader.mjs
index aa38eaa..cac97f8 100644
--- a/mixed-format/loader.mjs
+++ b/mixed-format/loader.mjs
@@ -3,21 +3,31 @@ export async function load(url, context, nextLoad) {
 
   const nextResult = await nextLoad(url, { ...context, format: 'module' })
     .then((result) => {
-      if (`${result.source}`.match(/exports[\. =]/)) throw new Error('Module is commonjs');
+      if (containsCJS(result.source)) { throw new Error('CommonJS'); }
 
       return result;
     })
     .catch(async (err) => {
       if (
         (err?.message.includes('require') && err.includes('import'))
-        || err?.message.includes('commonjs')
-      ) return {
-        format: 'commonjs',
-        source: (await nextLoad(url, {...context, format: 'commonjs' })).source,
-      };
+        || err?.message.includes('CommonJS')
+      ) {
+        return { format: 'commonjs' };
+      }
 
       throw err;
     });
 
   return nextResult;
 }
+
+function containsCJS(source) {
+  const src = '' + source;
+
+  if (src.match(/exports[\.( ?=)]/)) return true;
+
+  if (
+    src.match(/require\(/)
+    && !src.match(/createRequire\(/)
+  ) return true;
+}

From 86ef7ce083914980817c33b1ca81dd7db9d6e958 Mon Sep 17 00:00:00 2001
From: Jacob Smith <3012099+JakobJingleheimer@users.noreply.github.com>
Date: Wed, 31 Aug 2022 12:18:18 +0200
Subject: [PATCH 3/3] Update mixed-format/loader.mjs

Co-authored-by: Geoffrey Booth <456802+GeoffreyBooth@users.noreply.github.com>
---
 mixed-format/loader.mjs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mixed-format/loader.mjs b/mixed-format/loader.mjs
index cac97f8..afb903a 100644
--- a/mixed-format/loader.mjs
+++ b/mixed-format/loader.mjs
@@ -24,7 +24,8 @@ export async function load(url, context, nextLoad) {
 function containsCJS(source) {
   const src = '' + source;
 
-  if (src.match(/exports[\.( ?=)]/)) return true;
+  // A realistic version of this loader would use a parser like Acorn to check for actual `module.exports` syntax
+  if (src.match(/exports[\.( ?=)]/)) { return true };
 
   if (
     src.match(/require\(/)