biomejs · arendjr · Jul 16, 2025 · Jul 16, 2025
diff --git a/.changeset/damned-definitions-differ.md b/.changeset/damned-definitions-differ.md
@@ -0,0 +1,5 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed [#6829](https://github.com/biomejs/biome/issues/6829): Fixed a false positive reported by `useImportExtensions` when importing a `.js` file that had a matching `.d.ts` file in the same folder.
diff --git a/crates/biome_js_analyze/src/lint/correctness/use_import_extensions.rs b/crates/biome_js_analyze/src/lint/correctness/use_import_extensions.rs
@@ -215,19 +215,22 @@ fn get_extensionless_import(
         return None;
     }
 
-    // In cases like `./foo.css` -> `./foo.css.ts`
-    let resolved_path_has_sub_extension = resolved_path
-        .file_stem()
-        .is_some_and(|stem| stem.contains('.'));
-    let existing_extension = path.extension();
+    let resolved_stem = resolved_path.file_stem();
+    let resolved_extension = resolved_path.extension();
+    let resolved_path_sub_extension =
+        resolved_stem.and_then(|stem| stem.rfind('.').map(|pos| &stem[pos + 1..]));
 
-    if resolved_path_has_sub_extension && path.file_name()?.starts_with(resolved_path.file_name()?)
-    {
-        return None;
-    }
+    let existing_extension = path.extension();
 
-    if !resolved_path_has_sub_extension && existing_extension.is_some() {
-        return None;
+    match (resolved_path_sub_extension, existing_extension) {
+        (Some("d"), Some("js")) if resolved_extension.is_some_and(|ext| ext == "ts") => {
+            return None; // We resolved a `.d.ts` file, but imported the `.js` file: OK.
+        }
+        (Some(_), _) if path.file_name()?.starts_with(resolved_path.file_name()?) => {
+            return None; // For cases like `./foo.css` -> `./foo.css.ts`
+        }
+        (None, Some(_)) => return None,
+        _ => {}
     }
 
     let last_component = path_components.next_back().unwrap_or(first_component);
@@ -244,12 +247,10 @@ fn get_extensionless_import(
     let extension = if force_js_extensions {
         "js"
     } else {
-        resolved_path.extension()?
+        resolved_extension?
     };
 
-    let is_index_file = resolved_path
-        .file_stem()
-        .is_some_and(|stem| stem == "index");
+    let is_index_file = resolved_stem.is_some_and(|stem| stem == "index");
 
     let new_path = if is_index_file {
         let mut path_parts = path.as_str().split('/');
@@ -274,7 +275,7 @@ fn get_extensionless_import(
         new_path
     } else {
         let mut new_path = path.to_path_buf();
-        let sub_extension = if resolved_path_has_sub_extension {
+        let sub_extension = if resolved_path_sub_extension.is_some() {
             existing_extension
         } else {
             None

diff --git a/crates/biome_js_analyze/tests/specs/correctness/useImportExtensions/sub/generated/index.d.ts b/crates/biome_js_analyze/tests/specs/correctness/useImportExtensions/sub/generated/index.d.ts
diff --git a/...iome_js_analyze/tests/specs/correctness/useImportExtensions/sub/generated/index.d.ts.snap b/...iome_js_analyze/tests/specs/correctness/useImportExtensions/sub/generated/index.d.ts.snap
diff --git a/crates/biome_js_analyze/tests/specs/correctness/useImportExtensions/sub/generated/index.js b/crates/biome_js_analyze/tests/specs/correctness/useImportExtensions/sub/generated/index.js
diff --git a/.../biome_js_analyze/tests/specs/correctness/useImportExtensions/sub/generated/index.js.snap b/.../biome_js_analyze/tests/specs/correctness/useImportExtensions/sub/generated/index.js.snap
diff --git a/crates/biome_js_analyze/tests/specs/correctness/useImportExtensions/valid.js b/crates/biome_js_analyze/tests/specs/correctness/useImportExtensions/valid.js
@@ -25,3 +25,5 @@ import "./sub/component.svg.svelte.ts?query=string&query2#hash";
 import './sub/baz';
 import './sub/baz.css';
 import './sub/baz.css.com';
+
+import "./sub/generated/index.js";
diff --git a/crates/biome_js_analyze/tests/specs/correctness/useImportExtensions/valid.js.snap b/crates/biome_js_analyze/tests/specs/correctness/useImportExtensions/valid.js.snap
@@ -32,4 +32,6 @@ import './sub/baz';
 import './sub/baz.css';
 import './sub/baz.css.com';
 
+import "./sub/generated/index.js";
+
 ```