[red-knot] Add a new Type::KnownInstanceType variant#14155
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Type::KnownInstanceType variant
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carljm
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Nov 7, 2024
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| Type::Instance(InstanceType { | ||
| class: class_literal.class, | ||
| }) |
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We do this a lot in this PR, I wonder about a Class::to_instance_type() method for it?
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This can be considered separately as a follow-up if it's worth it
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I think I might resolve conflicts and land this, if that's OK with you? I'm realizing that I think I want to represent a TypeVar (not as a type, but the type of the typevar's own symbol, e.g. |
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Go for it! It's late here and I'm still travelling back from choir 👍 |
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Summary
Fixes #14114. I don't think I can really describe the problems with our current architecture (and therefore the motivations for this PR) any better than @carljm did in that issue, so I'll just copy it out here!
We currently represent "known instances" (e.g. special forms like
typing.Literal, which are an instance oftyping._SpecialForm, but need to be handled differently from other instances oftyping._SpecialForm) as anInstanceTypewith aknownfield that isSome(...).This makes it easy to handle a known instance as if it were a regular instance type (by ignoring the
knownfield), and in some cases (e.g.Type::member) that is correct and convenient. But in other cases (e.g.Type::is_equivalent_to) it is not correct, and we currently have a bug that we would consider the known-instance type oftyping.Literalas equivalent to the general instance type fortyping._SpecialForm, and we would fail to consider it a singleton type or a single-valued type (even though it is both.)An instance type with
known.is_some()is semantically quite different from an instance type withknown.is_none(). The former is a singleton type that represents exactly one runtime object; the latter is an open type that represents many runtime objects, including instances of unknown subclasses. It is too error-prone to represent these very-different types as a singleTypevariant. We should instead introduce a dedicatedType::KnownInstancevariant and force ourselves to handle these explicitly in allTypevariant matches.Possible followups
There is still a little bit of awkwardness in our current design in some places, in that we first infer the symbol
typing.Literalas a_SpecialForminstance, and then later convert that instance-type into a known-instance-type. We could also use thisKnownInstanceTypeenum to account for other special runtime symbols such asbuiltins.Ellipsisorbuiltins.NotImplemented.I think these might be worth pursuing, but I didn't do them here as they didn't seem essential right now, and I wanted to keep the diff relatively minimal.
Test Plan
cargo test -p red_knot_python_semantic. New unit tests added forType::is_subtype_of.