Intersection types & type checks

[JaroslavTulach]

Pull Request Description

Implementation of type checks for intersection types. The idea is to split the list of types[] in EnsoMultiValue into two parts:

• first methodDispatchTypes represent the types the value "has been cast to"
• the rest of the types represent the types the value "can be cast to"

By performing this separation we address the #10882 requirements. After a type check only methods available on the methodDispatchTypes can be invoked. However the value can still be cast to all the possible types.

Important Notes

@Akirathan, @radeusgd please check the idea, feel free to contribute new test cases. The goal of this PR is to get the dispatch/cast logic right. The next step would be to make it fast.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.

[Akirathan]

Idea for increasing test coverage of EnsoMultiValue: Manually create some Truffle nodes and explicitly call them. Inspiration from EqualsTest and HashCodeTest.

[GregoryTravis]

Approve libs change.

[JaroslavTulach]

Idea for increasing test coverage of EnsoMultiValue: Manually create some Truffle nodes and explicitly call them. Inspiration from EqualsTest and HashCodeTest.

• some EnsoMultiValue tests have just been created as part of Giving TypeOfNode richer query API #11618
• I have a much better feeling with such tests!

[JaroslavTulach]

Open question: what's the desired behavior in this (x : Text & Integer) : Text case?

• assertFalse("4 != t4", equalityCheck(4L, fourExtraText));
• assertTrue("4 == t4",equalityCheck(4L, fourExtraText));

Does the final object can still be equal - e.g. represent Integer (without being casted to it) - or it can only be equal to Text?

Resolution: Since be5dbe8 the obj : Text cannot be equal to Integer. The extra Integer type is shadowed:

• one would have to cast the object again (obj : Text) : Integer to be equal to integer (but then it would be no longer equal to Text)
• one would have to cast the object to both (obj : Text) : (Integer & Text) to be equal to both integer and the text

This way we respect the ascribed type of a value while allowing it to be cast to the extra types and get extra behavior.

[JaroslavTulach]

Turns out that these types are mutually exclusive:

The following type combinations are mutually exclusive and cannot return true for the type check message of the same receiver value:
Null
Boolean
String
Number
Date, Time or TimeZone
Duration
Exception
Meta-Object
Iterator

as such the following find method always selects at most one of the above types and that is the interop type of the multi value.

[JaroslavTulach]

If we want the call to to_b_to_c x to fail, then we need to restrict the from conversions of EnsoMultiValue only to the methodDispatchTypes...