Use generics to type data property in GrayMatterFile interface

[michaeljota]

I originally posted this in #67, but I realize that this is actually a bug when using Typescript.

I would like to type the data property in GrayMatterFile interface. With a generic type, of curse. Could be done with this:

  interface GrayMatterFile<T = any, I extends Input = Input> {
    data: T;
    content: string;
    excrept?: string;
    orig: Buffer | I;
    language: string;
    matter: string;
    stringify(lang: string): string;
  }

Using default generics again, allow this to keep backward compatibility, if the T is declared after the I.

  interface GrayMatterFile<I extends Input = Input, T = any> {
    data: T;
    content: string;
    excrept?: string;
    orig: Buffer | I;
    language: string;
    matter: string;
    stringify(lang: string): string;
  }

---

This is because object does not allow accessing any custom properties, so effectively there are only a couple of properties that you can access when using this with Typescript. By using generics, developers are allowed to shape that property as they probably now the actual model of data property. By using defaults, if the developer does not provide a type, then data will be any, allowing to access any custom property.

[robertmassaioli]

In 4.0.2 we have used the type { [key: string]: any; } because without validation that the parsed frontmatter matches the type T, it is probably not a good idea to just cast the read-in type to T. It's just going to result in unexpected errors.

You can add a validation + typecast logic on top of that type if you like.

At any rate, I'm going to close this as "won't fix". Cheers.