fix(dts): prefer declaration extensions over JS in exports-resolved paths

fixtures/pnpm/package.json

@@ -7,6 +7,7 @@
     "axios": "1.8.4",
     "decimal.js": "10.5.0",
     "ipaddr.js": "2.2.0",
+    "magic-string": "0.30.17",
     "mathjs": "14.4.0",
     "minimatch": "10.0.1",
     "postcss": "8.5.3",

napi/tests/dts.test.mjs

@@ -0,0 +1,20 @@
+import { join } from "node:path";
+import { fileURLToPath } from "node:url";
+import { assert, test } from "vitest";
+
+import { ResolverFactory } from "../index.js";
+
+const currentDir = join(fileURLToPath(import.meta.url), "..");
+const rootDir = join(currentDir, "..", "..");
+const pnpmDir = join(rootDir, "fixtures", "pnpm");
+
+const resolver = new ResolverFactory({
+  conditionNames: ["import", "types"],
+});
+
+test("magic-string resolves to .d.mts", () => {
+  const containingFile = join(pnpmDir, "index.ts");
+  const result = resolver.resolveDtsSync(containingFile, "magic-string");
+  assert.isUndefined(result.error);
+  assert.match(result.path, /magic-string\.es\.d\.mts$/);
+});

src/dts_resolver.rs

@@ -593,13 +593,16 @@ impl<Fs: FileSystem> ResolverGeneric<Fs> {
     }
 
     fn dts_resolve_esm_match(&self, cached_path: &CachedPath, ctx: &mut Ctx) -> Option<CachedPath> {
+        // Try declaration/TS extension substitution first (e.g. .mjs -> .d.mts)
+        let extensions = Extensions::TYPESCRIPT.union(Extensions::DECLARATION);
+        if let Some(path) = self.dts_resolve_as_file(extensions, cached_path, ctx) {
+            return Some(path);
+        }
+        // Fall back to original file if it exists
         if self.cache.is_file(cached_path, ctx) {
             return Some(cached_path.clone());
         }
-        // Try as file with TS extensions
-        let extensions =
-            Extensions::TYPESCRIPT.union(Extensions::DECLARATION).union(Extensions::JAVASCRIPT);
-        self.dts_resolve_as_file(extensions, cached_path, ctx)
+        None
     }
 
     // -------- @types name mangling --------

src/tests/dts_resolver.rs

@@ -173,6 +173,19 @@ fn no_types_not_resolved() {
     assert_eq!(result.path(), dts_fixture().join("node_modules/no-types/index.js"));
 }
 
+// -------- exports: ESM match finds declaration over JS --------
+
+#[test]
+fn exports_esm_match_finds_declaration() {
+    // When exports resolves to .mjs but .d.mts exists, prefer .d.mts
+    let r = resolver();
+    let result = r.resolve_dts(containing_file(), "exports-dts-for-mjs").unwrap();
+    assert_eq!(
+        result.path(),
+        dts_fixture().join("node_modules/exports-dts-for-mjs/dist/index.d.mts")
+    );
+}
+
 // -------- @types name mangling --------
 
 #[test]