lit-helpers spreadProps types

[oligafner]

Expected behavior

When I use spreadPros like this:

const item: InterfaceItem...
${spreadProps(item)}

it would expect it to throw no error

Actual Behavior

When I use spreadPros like this:

const item: InterfaceItem...
${spreadProps(item)}

I get a TypeScript error

Argument of type 'InterfaceItem' is not assignable to parameter of type '{ [key: string]: unknown; }'.
  Index signature for type 'string' is missing in type 'InterfaceItem'.

my Interface looks like this

interface InterfaceItem {
  text?: string;
}

I can work around this when i spread my object like this:

${spreadProps({...item})}

Additional context

if I change the type definition from

export declare const spreadProps: (_spreadData: {
    [key: string]: unknown;
})

to

export declare const spreadProps: (_spreadData: {
    [key: string]: any;
})

there is no error thrown, but i don't know if this is the right approach. Could also be related to this: microsoft/TypeScript#50087 (comment)

[Westbrook]

It’s possible that a generic could help here, but there is a pretty vast (see the looseness of the internal type) amount of values to cover here. If you had a suggestion in the form of a PR, we’d be happy to discuss this more closely!