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[ty] Return Option<TupleType> from infer_tuple_type_expression (#19735 )

## Summary

This PR reduces the virality of some of the `Todo` types in
`infer_tuple_type_expression`. Rather than inferring `Todo`, we instead
infer `tuple[Todo, ...]`. This reflects the fact that whatever the
contents of the slice in a `tuple[]` type expression, we would always
infer some kind of tuple type as the result of the type expression. Any
tuple type should be assignable to `tuple[Todo, ...]`, so this shouldn't
introduce any new false positives; this can be seen in the ecosystem
report.

As a result of the change, we are now able to enforce in the signature
of `Type::infer_tuple_type_expression` that it returns an
`Option<TupleType<'db>>`, which is more strongly typed and expresses
clearly the invariant that a tuple type expression should always be
inferred as a `tuple` type. To enable this, it was necessary to refactor
several `TupleType` constructors in `tuple.rs` so that they return
`Option<TupleType>` rather than `Type`; this means that callers of these
constructor functions are now free to either propagate the
`Option<TupleType<'db>>` or convert it to a `Type<'db>`.

## Test Plan

Mdtests updated.

2025-08-04 13:48:19 +01:00

486 B

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Starred expression annotations

[environment]
python-version = "3.11"

Type annotations for *args can be starred expressions themselves:

from typing_extensions import TypeVarTuple

Ts = TypeVarTuple("Ts")

def append_int(*args: *Ts) -> tuple[*Ts, int]:
    reveal_type(args)  # revealed: @Todo(PEP 646)

    return (*args, 1)

# TODO should be tuple[Literal[True], Literal["a"], int]
reveal_type(append_int(True, "a"))  # revealed: tuple[@Todo(PEP 646), ...]

486 B Raw Blame History

Starred expression annotations

486 B

Raw Blame History