cater for shapes where keys are not all strings

Author: nwaughachukwuma

common/api-review/firestore-lite.api.md

@@ -14,7 +14,7 @@ export function addDoc<T>(reference: CollectionReference<T>, data: WithFieldValu
 
 // @public
 export type AddPrefixToKeys<Prefix extends string, T extends Record<string, unknown>> = {
-    [K in keyof T & string as `${Prefix}.${K}`]+?: T[K];
+    [K in keyof T as K extends string ? `${Prefix}.${K}`: K]+?: T[K]
 };
 
 // @public

common/api-review/firestore.api.md

@@ -14,7 +14,7 @@ export function addDoc<T>(reference: CollectionReference<T>, data: WithFieldValu
 
 // @public
 export type AddPrefixToKeys<Prefix extends string, T extends Record<string, unknown>> = {
-    [K in keyof T & string as `${Prefix}.${K}`]+?: T[K];
+    [K in keyof T as K extends string ? `${Prefix}.${K}`: K]+?: T[K]
 };
 
 // @public

packages/firestore/src/lite-api/types.ts

@@ -66,7 +66,7 @@ export type AddPrefixToKeys<
   T extends Record<string, unknown>
 > =
   // Remap K => Prefix.K. See https://www.typescriptlang.org/docs/handbook/2/mapped-types.html#key-remapping-via-as
-  { [K in keyof T & string as `${Prefix}.${K}`]+?: T[K] };
+  { [K in keyof T as K extends string ? `${Prefix}.${K}`: K]+?: T[K] };
 
 /**
  * Given a union type `U = T1 | T2 | ...`, returns an intersected type