__reversed__ with an explicit Iterator[T] return annotation synthesizes IReverseEnumerable[Iterator[T]], not IReverseEnumerable[T]

Measured on v5/clr-resolution (visible only once IReverseEnumerable[int] became nameable again — P4 remediation R4; at 311252e33 the annotation itself was SPY0202, so the mismatch was masked).

class Bag:
    _items: list[int]

    def __init__(self) -> None:
        self._items = [4, 5]

    def __reversed__(self) -> Iterator[int]:
        return reversed(self._items)

def take(r: IReverseEnumerable[int]) -> None:
    for x in r:
        print(x)

def main() -> None:
    take(Bag())

error[SPY0220]: Cannot pass argument of type 'Bag' to parameter of type 'IReverseEnumerable[int32]'

Changing the parameter to IReverseEnumerable[Iterator[int]] makes the argument bind (it then fails later on #1808, iterating an interface-typed receiver), so the synthesized interface's type argument is the __reversed__ return annotation verbatim rather than its element type.

The generator shape is correct: def __reversed__(self) -> int: yield ... synthesizes IReverseEnumerable[int] and take(c) binds (SynthesizedInterfaceVisibilityTests.Reversed_Class_ElementTypeFromAnnotation, and Integration/TestFixtures/interop/sharpy_interface_by_name_1625.spy). Only the non-generator arm — an explicit Iterator[T] / IEnumerator[T] return — takes the annotation unpeeled.

The element-type decision belongs to the one iterable-element decider (InferReversedElementType and friends), which should unwrap an iterator/iterable return the same way the generator arm does. Same family as the P9 ClassifyIterableSource consolidation.

fix(semantic): an explicitly written Sharpy-namespace type name resol…

Placement (2026-09-11 batching): P10, with #1850 and #1868 under the one iterable-element decider: every producer (a __reversed__/__iter__ return annotation) and consumer (for, comprehension, yield from, list()/set()/… constructors, reversed, sum/min/max, in) asks the same decider; a non-iterable is a named refusal at every consumer. Reproduced @ 41dd19d (SPY0220 Bag into IReverseEnumerable[int32]).

fix(semantic): one iterable-element decider — a producer annotation's…

fix(codegen): enumerator members read the synthesized interface's ele…

fix(semantic): a non-iterable argument to list/set/frozenset/dict is …

fix(semantic): a generator annotated Iterator[T] is refused with a st…

test(semantic): iterable producer/consumer matrices, constructor-ring…

Closed by P10 (plan-f164be), Phase 3 — commits 8b6668b42 (IterableElementDecider + producers) + da71f0ca3 (emitter reads the materialized element) + 3b7a0293b (matrices/fixtures).

Acceptance:

IterableElementDeciderConformanceTests 10/10; IterableProducerAnnotationMatrixTests green. Emitter annotation-map source scan pre-fix count 4 → 0 (all 4 arms via FindSynthesizedInterface/GetSynthesizedElementType). Mutation: restore MapType(funcDef.ReturnType) → c02c red while the slot cell stays green; remove the non-generator row → c03/b14 red.
By direction: c02c reversed(r) with __reversed__ -> Iterator[int] was SPY0908 CS0266, now prints 5 4; c02 element probe names int32; c03 e: IEnumerable[int] = Bag() binds and runs 1 2; list(Bag()) → [1, 2].

Whole-solution gate GREEN 31390 passed / 0 failed / 3 skipped @ ed7a5fe (Core 2715, Cli 337, Lsp 1053 incl. FrontEndParity, Stdlib 3773, Compiler.Tests 23512/0/3 incl. the 3 GapDiscovery sweeps).

docs+test: producer-annotation rule in dunder_methods.md, the P10 ann…

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reversed with an explicit Iterator[T] return annotation synthesizes IReverseEnumerable[Iterator[T]], not IReverseEnumerable[T] #1832

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__reversed__ with an explicit Iterator[T] return annotation synthesizes IReverseEnumerable[Iterator[T]], not IReverseEnumerable[T] #1832

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antonsynd commented on Sep 12, 2026

antonsynd commented on Sep 19, 2026

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reversed with an explicit Iterator[T] return annotation synthesizes IReverseEnumerable[Iterator[T]], not IReverseEnumerable[T] #1832