allow to inherit imports from amended file

[lucsoft]

Allowing to have implicit imports would remove the boilerplate of splitting up files.

Current use case would be to not need to reimport all the Kubernetes imports for each file.

[bioball]

I definitely see the reason you might want this. However, this can introduce quite hidden bugs. If the parent's imports were resolvable in an amending module, this means that you can possibly change the meaning of a variable in a child module by simply adding an import.

For example:

// parent.pkl
class Bird {
  name: String
  scientificName: String
}

bird: Bird

// child.pkl
amends "parent.pkl"

bird {
  scientificName = name // `name` is not in lexical scope, fall back to looking up `this.name`
}

Here, name resolves to an implicit this.name because name is not available in child.pkl's lexical scope.

If we allowed the child module to see imports declared in the parent, that means that we can change what scientificName = name resolves to, by adding this import:

// parent.pkl

+import "name.pkl"

 class Bird {
   name: String
   scientificName: String
 }

 bird: Bird

This type of behavior can cause hidden bugs; adding a new import can unintentionally cause a variable's resolution to change.

[bioball]

Note: often, you don't need to re-import in amending modules. Let's use the same example from above, but move Bird into its own module.

// parent.pkl
import "Bird.pkl"

bird: Bird

birds: Listing<Bird>

An amending module does not need to then re-import Bird to define an instance of it. Instead, you can simply amend values of type Bird directly, or create instances with the new keyword in positions where Pkl can infer the parent (like in the case of Listing<Bird>.

amends "parent.pkl"

bird {
  name = "Warbler"
  scentificName = "Parulidae"
}

birds {
  new { name = "Warbler"; scientificName = "Parulidae" }
}