Disallow inheritance from breaking generic constraints

[Graveflo]

Summary

Inheriting from an object that has a constraint allows the constraint of the base class to be broken without warning.

type
  SomeThing = distinct object
  BaseClass[T: SomeThing] = object of RootObj
    encap: T
  IEraseConstraint[T] = object of BaseClass[T]

discard IEraseConstraint[int]()

Description

In the following example, either IEraseConstraint[T] = object of BaseClass[T] for it's lack of verbosity or IEraseConstraint[int]() for its breaking of base class constrains, should be a compile time error or warning.

Alternatives

No response

Examples

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Backwards Compatibility

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Links

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[metagn]

Related: #21181

I think the "wildcard" generic parameters are allowed to pass any constraint early on (at the generic declaration) but then the constraint is not checked during instantiation

[Graveflo]

Interesting. Sounds like that might be a fairly straight forward fix.
This pattern is very easy to do by mistake and can lead to unintended program states. I think that a warning would go a long way here if nothing else because the constraints can be restated. However, more consistent with the rest of the language and in a design where safety is critical, an error makes the most sense.