[ty] Promote literals when inferring class specializations from constructors #18102
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dcreager
commented
May 14, 2025
| // typevars that are inferred as a literal to the corresponding instance type. | ||
| builder | ||
| .build(gc) | ||
| .apply_type_mapping(db, &TypeMapping::PromoteLiterals) |
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…rals * origin/main: [ty] Add type-expression syntax link to invalid-type-expression (#18104) [`flake8-simplify`] add fix safety section (`SIM103`) (#18086) [ty] mypy_primer: fix static-frame setup (#18103) [`flake8-simplify`] Correct behavior for `str.split`/`rsplit` with `maxsplit=0` (`SIM905`) (#18075) [ty] Fix more generics-related TODOs (#18062)
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AlexWaygood
reviewed
May 14, 2025
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This implements the stopgap approach described in astral-sh/ty#336 (comment) for handling literal types in generic class specializations.
With this approach, we will promote any literal to its instance type, but only when inferring a generic class specialization from a constructor call:
If you specialize the class explicitly, we still use whatever type you provide, even if it's a literal:
And this doesn't apply at all to generic functions:
As part of making this happen, we also generalize the
TypeMappingmachinery. This provides a way to apply a function to type, returning a new type. Compicating matters is that for function literals, we have to apply the mapping lazily, since the function's signature is not created until (and if) someone calls itssignaturemethod. That means we have to stash away the mappings that we want to apply to the signatures parameter/return annotations once we do create it. This requires some minorCowshenanigans to continue working for partial specializations.