From f3350696c8b30b1291508b1fc17815882f52410b Mon Sep 17 00:00:00 2001
From: chouzz <zhouhua258@outlook.com>
Date: Tue, 12 May 2026 23:40:16 +0800
Subject: [PATCH] fix: apply ESM .js extension fallback to tsconfig path alias
 resolution

Path alias imports (e.g. `@/utils.js` via tsconfig paths) now correctly
strip JS-family extensions and retry with TS equivalents when the literal
.js file does not exist. This applies the same stripJsExtension fallback
already used for relative imports to the alias resolution branch.

Fixes #1528
---
 .../ingestion/import-resolvers/standard.ts    | 10 ++-
 .../unit/esm-extension-resolution.test.ts     | 64 +++++++++++++++++++
 2 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/gitnexus/src/core/ingestion/import-resolvers/standard.ts b/gitnexus/src/core/ingestion/import-resolvers/standard.ts
index 47e2dabb2..4ee6e1440 100644
--- a/gitnexus/src/core/ingestion/import-resolvers/standard.ts
+++ b/gitnexus/src/core/ingestion/import-resolvers/standard.ts
@@ -72,6 +72,13 @@ export const resolveImportPath = (
         const resolved = tryResolveWithExtensions(rewritten, allFiles);
         if (resolved) return cache(resolved);
 
+        // ESM fallback: strip .js/.jsx/.mjs/.cjs and retry with TS equivalents
+        const strippedAlias = stripJsExtension(rewritten);
+        if (strippedAlias !== null) {
+          const esmResolved = tryResolveWithExtensions(strippedAlias, allFiles);
+          if (esmResolved) return cache(esmResolved);
+        }
+
         // Try suffix matching as fallback
         const parts = rewritten.split('/').filter(Boolean);
         const suffixResult = suffixResolve(parts, normalizedFileList, allFileList, index);
@@ -132,9 +139,6 @@ export const resolveImportPath = (
 
     // TypeScript ESM: imports use .js/.jsx/.mjs/.cjs but source files are
     // .ts/.tsx/.mts/.cts. Strip the JS-family extension and re-resolve.
-    // NOTE: This fallback only applies to relative imports. Path alias imports
-    // (e.g. @/utils.js via tsconfig paths) do not yet strip .js extensions —
-    // that is a known limitation tracked for follow-up.
     if (language === SupportedLanguages.TypeScript || language === SupportedLanguages.JavaScript) {
       const stripped = stripJsExtension(basePath);
       if (stripped !== null) {
diff --git a/gitnexus/test/unit/esm-extension-resolution.test.ts b/gitnexus/test/unit/esm-extension-resolution.test.ts
index 69dc652cf..a10a79f57 100644
--- a/gitnexus/test/unit/esm-extension-resolution.test.ts
+++ b/gitnexus/test/unit/esm-extension-resolution.test.ts
@@ -151,3 +151,67 @@ describe('stripJsExtension', () => {
   it('returns null for .ts', () => expect(stripJsExtension('foo/bar.ts')).toBeNull());
   it('returns null for no extension', () => expect(stripJsExtension('foo/bar')).toBeNull());
 });
+
+describe('ESM extension resolution — path aliases with .js extensions', () => {
+  function resolveWithAlias(
+    currentFile: string,
+    importPath: string,
+    ctx: ReturnType<typeof makeCtx>,
+    aliases: [string, string][],
+    baseUrl = '.',
+  ): string | null {
+    return resolveImportPath(
+      currentFile,
+      importPath,
+      ctx.allFilesSet,
+      ctx.files,
+      ctx.normalized,
+      ctx.cache,
+      SupportedLanguages.TypeScript,
+      { aliases, baseUrl },
+      ctx.index,
+    );
+  }
+
+  it('resolves @/utils.js to src/utils.ts via alias', () => {
+    const ctx = makeCtx(['src/index.ts', 'src/utils.ts']);
+    const result = resolveWithAlias('src/index.ts', '@/utils.js', ctx, [['@/', 'src/']], '.');
+    expect(result).toBe('src/utils.ts');
+  });
+
+  it('resolves @/component.jsx to src/component.tsx via alias', () => {
+    const ctx = makeCtx(['src/index.ts', 'src/component.tsx']);
+    const result = resolveWithAlias(
+      'src/index.ts',
+      '@/component.jsx',
+      ctx,
+      [['@/', 'src/']],
+      '.',
+    );
+    expect(result).toBe('src/component.tsx');
+  });
+
+  it('prefers actual .js file over TS fallback in alias resolution', () => {
+    const ctx = makeCtx(['src/index.ts', 'src/utils.js', 'src/utils.ts']);
+    const result = resolveWithAlias('src/index.ts', '@/utils.js', ctx, [['@/', 'src/']], '.');
+    expect(result).toBe('src/utils.js');
+  });
+
+  it('resolves alias with baseUrl prefix', () => {
+    const ctx = makeCtx(['app/src/index.ts', 'app/src/helpers/token.ts']);
+    const result = resolveWithAlias(
+      'app/src/index.ts',
+      '~/helpers/token.js',
+      ctx,
+      [['~/', 'src/']],
+      'app',
+    );
+    expect(result).toBe('app/src/helpers/token.ts');
+  });
+
+  it('returns null when alias .js import has no matching source', () => {
+    const ctx = makeCtx(['src/index.ts']);
+    const result = resolveWithAlias('src/index.ts', '@/missing.js', ctx, [['@/', 'src/']], '.');
+    expect(result).toBeNull();
+  });
+});