refactor(config-loader): do not lookup package.json with explicit extensions

Currently when a config has an explicit extension, the config-loader
still tries resolving/traversing for a `package.json` file. This can
be slow, and also break in some environments with sandboxing; especially
when used in combination with Bazel.

It doesn't seem investigating why the calls are stuck, if the logic
should not run in general when an explicit extension is provided.

Author: devversion

.changeset/nice-guests-invent.md

@@ -0,0 +1,9 @@
+---
+'@web/config-loader': patch
+---
+
+Optimizes config loading to not look for `package.json` in file system if the
+config extension is already informing whether CommonJS or ESM is used.
+
+Currently config loading did unnecessarily traverse the file system. This could
+be unnecessary slowness, or cause issues in sandbox environments (like Bazel)

packages/config-loader/src/importOrRequireConfig.js

@@ -17,7 +17,6 @@ function importConfig(configPath) {
  * @param {string} basedir
  */
 async function importOrRequireConfig(configPath, basedir) {
-  const packageType = await getPackageType(basedir);
   const ext = path.extname(configPath);
 
   switch (ext) {
@@ -26,6 +25,7 @@ async function importOrRequireConfig(configPath, basedir) {
     case '.cjs':
       return requireConfig(configPath);
     default:
+      const packageType = await getPackageType(basedir);
       return packageType === 'module' ? importConfig(configPath) : requireConfig(configPath);
   }
 }