mirror of https://github.com/astral-sh/ruff
77f8fa6906
## Summary Previously if an explicit specialization failed (e.g. wrong number of type arguments or violates an upper bound) we just inferred `Unknown` for the entire type. This actually caused us to panic on an a case of a recursive upper bound with invalid specialization; the upper bound would oscillate indefinitely in fixpoint iteration between `Unknown` and the given specialization. This could be fixed with a cycle recovery function, but in this case there's a simpler fix: if we infer `C[Unknown]` instead of `Unknown` for an invalid attempt to specialize `C`, that allows fixpoint iteration to quickly converge, as well as giving a more precise type inference. Other type checkers actually just go with the attempted specialization even if it's invalid. So if `C` has a type parameter with upper bound `int`, and you say `C[str]`, they'll emit a diagnostic but just go with `C[str]`. Even weirder, if `C` has a single type parameter and you say `C[str, bytes]`, they'll just go with `C[str]` as the type. I'm not convinced by this approach; it seems odd to have specializations floating around that explicitly violate the declared upper bound, or in the latter case aren't even the specialization the annotation requested. I prefer `C[Unknown]` for this case. Fixing this revealed an issue with `collections.namedtuple`, which returns `type[tuple[Any, ...]]`. Due to https://github.com/astral-sh/ty/issues/1649 we consider that to be an invalid specialization. So previously we returned `Unknown`; after this PR it would be `type[tuple[Unknown]]`, leading to more false positives from our lack of functional namedtuple support. To avoid that I added an explicit Todo type for functional namedtuples for now. ## Test Plan Added and updated mdtests. The conformance suite changes have to do with `ParamSpec`, so no meaningful signal there. The ecosystem changes appear to be the expected effects of having more precise type information (including occurrences of known issues such as https://github.com/astral-sh/ty/issues/1495 ). Most effects are just changes to types in diagnostics. |
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| .. | ||
| legacy | ||
| pep695 | ||
| builtins.md | ||
| scoping.md | ||
| specialize_constrained.md | ||