Make form of product of two data types be type equivalent to a product of two forms

[golergka]

Is your feature request related to a problem? Please describe.

I like to split my forms into separate components that group related and reusable sets of inputs. For example, in my database I have independent record for "Entity" which controls it's top-level settings and "EntityRevision", which controls the data which is updated in a versioned manner. When I create entity for the first time, I want to create a form that will encompass fields both for "Entity" and first "EntityRevision" in it's history. But when user edits the entity, I want to create separate form for creating new revision that will only have controls for the data that changes from version to version.

Describe the solution you'd like

I create components for two groups of entities:

interface EntityFormData {
	entityData: string
}

interface RevisionFormData {
	revisionData: string
}

export function EntityFormBody({ form }: { form: UseFormReturn<EntityFormData> }) { /*...*/ }
export function RevisionFormBody({ form }: { form: UseFormReturn<RevisionFormData> }) { /*...*/ }

And then use the library to create a shared form that will get passed to both components:

export function RevisionFormBody({ form }: { form: UseFormReturn });

Unfortunately, currently I get this type error:

Type 'UseFormReturn<EntityFormData | RevisionFormData, any, undefined>' is not assignable to type 'UseFormReturn<EntityFormData>'.
  The types returned by 'watch()' are incompatible between these types.
    Type 'EntityFormData | RevisionFormData' is not assignable to type 'EntityFormData'.
      Type 'RevisionFormData' is not assignable to type 'EntityFormData'.

However, when I cast it manually, everything works. I haven't investigated this issue in depth, but I suspect that either all usages of these entities should be comparable, or at least a large enough subset. In my case, I just use Controller component to extract data about particular fields.

Describe alternatives you've considered

For now, I write the same code, but just use casts to solve this problem.