[feature request] Add new generic type to enable typing a generic AppForm

[Jaime02]

Hello!
I am trying to set up a custom context to wrap my forms in order to store state in an efficient way and have the ability of reading custom variables in my custom form fields.

The best approach I found is this one:

export type TForm = ReturnType<typeof useAppForm<any, any, any, any, any, any, any, any, any, any, any, any>>;

export interface FormContextProps<T extends TForm = TForm> {
  form: T;
  formMode: FormMode;  // My custom attribute stored in the context
}

const FormContext = createContext<FormContextProps<TForm> | undefined>(undefined);

export function FormContextProvider<T extends TForm>({
  form,
  formMode,
  children,
}: PropsWithChildren<FormContextProps<T>>) {
  return (
    <FormContext value={{ form, formMode }}>
      <form.AppForm>{children}</form.AppForm>
    </FormContext>
  );
}

Edit: I found that the type error occurs only if the form has a field which may be a JS File object 😵‍💫 Opening issue #2145
It causes the following type error when the form instance is passed to the context:

export default function App() {
  const { form } = useSampleForm();
  return (
    <>
      <h1>Simple Form Example</h1>
      <SampleForm form={form} />
    </>
  );
}

src/index.tsx(30,19): error TS2322: Type 'AppFieldExtendedReactFormApi<{ firstName: string; formMode: FormMode; formFile: File | null; }, FormValidateOrFn<{ firstName: string; formMode: FormMode; formFile: File | null; }> | undefined, ... 11 more ..., {}>' is not assignable to type 'AppFieldExtendedReactFormApi<any, any, any, any, any, any, any, any, any, any, any, any, { readonly TextInput: ({ ...props }: DetailedHTMLProps<InputHTMLAttributes<HTMLInputElement>, HTMLInputElement>) => Element; }, {}>'.
  Types of property 'pushFieldValue' are incompatible.
    Type '<TField extends never>(field: TField, value: (TField extends "formMode" | "firstName" | "formFile" | "formFile.text" | `formFile.text.${string}` | "formFile.name" | "formFile.size" | "formFile.type" | ... 9 more ... | `formFile.stream.${string}` ? DeepRecord<...>[TField] : never) extends any[] ? (any[] & (TField ext...' is not assignable to type '<TField extends never>(field: TField, value: any, options?: UpdateMetaOptions | undefined) => void'.
      Types of parameters 'value' and 'value' are incompatible.
        Type 'any' is not assignable to type 'never'.

I tried using AnyFormApi without success. Shall a new type of Any... be added to the library? Or maybe is there a better way of doing this? Thanks in advance ❤️

Link to the stackblitz sandbox: https://stackblitz.com/edit/tanstack-form-zz8oewgu

I guess this is related to #1921

[Jaime02]

I have found another way of creating the context which does not have this issue, see #2145 (comment)