From e34f006484d89c53dd4cac7cface3c4d70841e34 Mon Sep 17 00:00:00 2001
From: cm-ayf <cm.ayf2734@gmail.com>
Date: Sun, 3 Sep 2023 07:26:59 +0900
Subject: [PATCH] fix(register): extension-aware module resolution and format
 handling

---
 packages/register/esm.mts | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/packages/register/esm.mts b/packages/register/esm.mts
index 9835d10f6..a5f678183 100644
--- a/packages/register/esm.mts
+++ b/packages/register/esm.mts
@@ -31,11 +31,16 @@ const host: ts.ModuleResolutionHost = {
   fileExists: ts.sys.fileExists,
   readFile: ts.sys.readFile,
 }
+const EXTENSIONS: string[] = [ts.Extension.Ts, ts.Extension.Tsx, ts.Extension.Mts]
 
 export const resolve: ResolveFn = async (specifier, context, nextResolve) => {
   // entrypoint
   if (!context.parentURL) {
-    return { format: 'ts', url: specifier, shortCircuit: true }
+    return {
+      format: EXTENSIONS.some((ext) => specifier.endsWith(ext)) ? 'ts' : undefined,
+      url: specifier,
+      shortCircuit: true,
+    }
   }
 
   // import/require from external library
@@ -51,8 +56,12 @@ export const resolve: ResolveFn = async (specifier, context, nextResolve) => {
     moduleResolutionCache,
   )
 
-  // import from local project to local project
-  if (resolvedModule && !resolvedModule.isExternalLibraryImport) {
+  // import from local project to local project TS file
+  if (
+    resolvedModule &&
+    !resolvedModule.resolvedFileName.includes('/node_modules/') &&
+    EXTENSIONS.includes(resolvedModule.extension)
+  ) {
     return {
       format: 'ts',
       url: pathToFileURL(resolvedModule.resolvedFileName).href,
@@ -60,7 +69,10 @@ export const resolve: ResolveFn = async (specifier, context, nextResolve) => {
     }
   }
 
-  // import from local project to external library (or unknown something)
+  // import from local project to either:
+  // - something TS couldn't resolve
+  // - external library
+  // - local project non-TS file
   return nextResolve(specifier)
 }