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more human comment

This commit is contained in:
Douglas Creager 2025-12-10 15:00:53 -05:00
parent 095c2bbe39
commit 8ec6673230
1 changed files with 11 additions and 4 deletions
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15
crates/ty_python_semantic/src/types/call/bind.rs
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@ -3028,10 +3028,17 @@ impl<'a, 'db> ArgumentTypeChecker<'a, 'db> {
continue;
};
// Synthetic arguments (e.g., implicit `self`/`cls`) are not provided by the caller.
// Counting their types when computing variance would incorrectly block literal
// promotion (they often carry the class typevars in invariant position), so we ignore
// them for argument variance tracking.
// Below, we will possibly perform literal promotion on the types that we infer for
// each typevar. Whether we do so will depend on the variance of the typevar in the
// parameter type that each argument is mapped to.
//
// Note that we do not track the variance for synthetic `self` arguments. Those
// only exist for generic methods of a (possibly generic) class. The class instance
// is fixed for any generic method call, and shouldn't affect literal promotion.
// (This is true even for the constructors of a generic class: a `self` annotation
// on `__init__` limits which specializations the constructor overload applies to,
// but we rely on occurrences of a typevar in other parameters to determine whether
// to promote literals in the specialized generic class type.)
if !matches!(argument, Argument::Synthetic)
&& parameter.form == ParameterForm::Value
&& expected_type.has_typevar(self.db)