chore: Cleanup inherit in @babel/types (#18117)

packages/babel-types/src/utils/inherit.ts

@@ -1,14 +1,26 @@
 import type * as t from "../index.ts";
 
+type MaybeArray = unknown[] | null | undefined;
+
+type ArrayKeys<C> = {
+  [K in keyof C]: C[K] extends MaybeArray ? K : never;
+}[keyof C];
+
 export default function inherit<C extends t.Node, P extends t.Node>(
-  key: keyof C & keyof P,
+  key: ArrayKeys<C> & ArrayKeys<P>,
   child: C,
   parent: P,
 ): void {
   if (child && parent) {
-    // @ts-expect-error Could further refine key definitions
-    child[key] = Array.from(
-      new Set(([] as any[]).concat(child[key], parent[key]).filter(Boolean)),
+    const parentVal = parent[key] as MaybeArray;
+    if (!parentVal) return;
+
+    const childVal = child[key] as MaybeArray;
+
+    (child[key] as MaybeArray) = Array.from(
+      childVal
+        ? new Set([...childVal, ...parentVal].filter(Boolean))
+        : parentVal,
     );
   }
 }