fix(lint): lint/suspicous/noRedeclare should not report redeclarations for infer type in conditional types (#8417)

taga3s · web-flow · commit c3a255709cdb · 2025-12-16T07:36:40.000Z
diff --git a/.changeset/breezy-groups-hope.md b/.changeset/breezy-groups-hope.md
@@ -0,0 +1,5 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed [#7809](https://github.com/biomejs/biome/issues/7809): [`noRedeclare`](https://biomejs.dev/linter/rules/no-redeclare/) no longer reports redeclarations for `infer` type in conditional types.
diff --git a/crates/biome_js_analyze/src/lint/suspicious/no_redeclare.rs b/crates/biome_js_analyze/src/lint/suspicious/no_redeclare.rs
@@ -171,11 +171,14 @@ fn check_redeclarations_in_single_scope(scope: &Scope, redeclarations: &mut Vec<
                 //   A parameter can override a previous parameter.
                 // - when both are type parameter in different declarations.
                 //   A type parameter can be redeclared if they are in different declarations.
+                // - when both are infer types.
+                //   An infer type can be redeclared in the same conditional type.
                 if !(first_decl.is_mergeable(&decl)
                     || first_decl.is_parameter_like() && decl.is_parameter_like()
                     || first_decl.is_type_parameter()
                         && decl.is_type_parameter()
-                        && first_decl.syntax().parent() != decl.syntax().parent())
+                        && first_decl.syntax().parent() != decl.syntax().parent()
+                    || first_decl.is_infer_type() && decl.is_infer_type())
                 {
                     redeclarations.push(Redeclaration {
                         name: name.text().into(),
diff --git a/crates/biome_js_analyze/tests/specs/suspicious/noRedeclare/valid-conditional-type.ts b/crates/biome_js_analyze/tests/specs/suspicious/noRedeclare/valid-conditional-type.ts
@@ -1,3 +1,9 @@
 /* should not generate diagnostics */
 // Issue https://github.com/biomejs/biome/issues/2659
-type Test<T> = T extends Array<infer U> ? true : false
+type Test<T> = T extends Array<infer U> ? true : false
+
+type TestMultipleInfer<T extends readonly string[]> = T[number] extends
+  | `-${infer Base}`
+  | infer Base
+  ? Base
+  : never
diff --git a/crates/biome_js_analyze/tests/specs/suspicious/noRedeclare/valid-conditional-type.ts.snap b/crates/biome_js_analyze/tests/specs/suspicious/noRedeclare/valid-conditional-type.ts.snap
@@ -7,4 +7,11 @@ expression: valid-conditional-type.ts
 /* should not generate diagnostics */
 // Issue https://github.com/biomejs/biome/issues/2659
 type Test<T> = T extends Array<infer U> ? true : false
+
+type TestMultipleInfer<T extends readonly string[]> = T[number] extends
+  | `-${infer Base}`
+  | infer Base
+  ? Base
+  : never
+
 ```
diff --git a/crates/biome_js_syntax/src/binding_ext.rs b/crates/biome_js_syntax/src/binding_ext.rs
@@ -199,6 +199,11 @@ impl AnyJsBindingDeclaration {
         matches!(self, Self::TsTypeParameter(_))
     }
 
+    /// Returns `true` if `self` is an infer type.
+    pub const fn is_infer_type(&self) -> bool {
+        matches!(self, Self::TsInferType(_))
+    }
+
     /// Returns the export statement if this declaration is directly exported.
     pub fn export(&self) -> Option<JsExport> {
         let maybe_export = match self {

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +"@biomejs/biome": patch
 +---
++
 +Fixed [#7809](https://github.com/biomejs/biome/issues/7809): [`noRedeclare`](https://biomejs.dev/linter/rules/no-redeclare/) no longer reports redeclarations for `infer` type in conditional types.