module: no type module resolver side effects

PR-URL: #33086
Reviewed-By: Jan Krems <jan.krems@gmail.com>
Reviewed-By: Geoffrey Booth <webmaster@geoffreybooth.com>

Author: guybedford

doc/api/esm.md

@@ -1605,13 +1605,6 @@ The resolver can throw the following errors:
 >       1. Return **PACKAGE_EXPORTS_TARGET_RESOLVE**(_packageURL_,
 >          _mainExport_, _""_).
 >    1. Throw a _Package Path Not Exported_ error.
-> 1. If _pjson.main_ is a String, then
->    1. Let _resolvedMain_ be the URL resolution of _packageURL_, "/", and
->       _pjson.main_.
->    1. If the file at _resolvedMain_ exists, then
->       1. Return _resolvedMain_.
-> 1. If _pjson.type_ is equal to _"module"_, then
->    1. Throw a _Module Not Found_ error.
 > 1. Let _legacyMainURL_ be the result applying the legacy
 >    **LOAD_AS_DIRECTORY** CommonJS resolver to _packageURL_, throwing a
 >    _Module Not Found_ error for no resolution.

lib/internal/modules/esm/resolve.js

@@ -439,11 +439,6 @@ function packageMainResolve(packageJSONUrl, packageConfig, base, conditions) {
 
       throw new ERR_PACKAGE_PATH_NOT_EXPORTED(packageJSONUrl, '.');
     }
-    if (packageConfig.main !== undefined) {
-      const resolved = new URL(packageConfig.main, packageJSONUrl);
-      const path = fileURLToPath(resolved);
-      if (tryStatSync(path).isFile()) return resolved;
-    }
     if (getOptionValue('--experimental-specifier-resolution') === 'node') {
       if (packageConfig.main !== undefined) {
         return finalizeResolution(
@@ -453,9 +448,7 @@ function packageMainResolve(packageJSONUrl, packageConfig, base, conditions) {
           new URL('index', packageJSONUrl), base);
       }
     }
-    if (packageConfig.type !== 'module') {
-      return legacyMainResolve(packageJSONUrl, packageConfig);
-    }
+    return legacyMainResolve(packageJSONUrl, packageConfig);
   }
 
   throw new ERR_MODULE_NOT_FOUND(

test/es-module/test-esm-type-main.mjs

@@ -0,0 +1,9 @@
+import { mustNotCall } from '../common/index.mjs';
+import assert from 'assert';
+import { importFixture } from '../fixtures/pkgexports.mjs';
+
+(async () => {
+  const m = await importFixture('type-main');
+  assert.strictEqual(m.default, 'asdf');
+})()
+.catch(mustNotCall);