Cater for shapes where keys are not all strings in AddPrefixToKeys interface definition

[nwaughachukwuma]

Summary

Fixes #6105

The issue comes from AddPrefixToKeys interface, shown below, in use cases where nested interfaces are defined as Record<string, Model> or {[key: string]: Model} - it looks like Typescript has a challenge inferring such shape as it considers K to be of type string|number|symbol.

export declare type AddPrefixToKeys<Prefix extends string, T extends Record<string, unknown>> = {
  [K in keyof T & string as`${Prefix}.${K}`]+?: T[K];
};

To solve this, we have to tell Typescript to infer the type or use a conditional statement to determine the type as shown below. Now, typescript can infer K and know its shape n-levels deep.

export declare type AddPrefixToKeys<Prefix extends string, T extends Record<string, unknown>> = {
  [K in keyof T as K extends string ? `${Prefix}.${K}`: K]+?: T[K];
};

This Typescript playground shows what's happening - all interface definitions come from the current version of firebase-js-sdk (firebase v9.7.0). I've commented the current logic for the fix. Switch between the 2 to see how the fix solves the issue

cc @ehsannas

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[ehsannas]

Thanks @nwaughachukwuma for your contribution, and apologies that this had fallen off my task list.

[felixgabler]

Hi! Is anyone working on this? Would be really awesome to fix.

[MarkDuckworth]

@nwaughachukwuma, apologies for the long delay on this. I've been looking at this recently and I'd like to accept the change, but I'm having trouble getting this solution to work. In the Typescript playground sample you linked, you can see the error when assigning to q on line 29. Still looking for a fix.

[nwaughachukwuma]

Hi @MarkDuckworth, it's been a while but let me take another look at it.