Allow yield with nullable/union return types by checking each union member for an iterable, non-array part#5903
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… member for an iterable, non-array part - `YieldInGeneratorRule` now flattens the declared return type and accepts it when at least one member is iterable and not an array (Generator, Iterator, Traversable, iterable). This mirrors PHP, which permits `?Generator`, `Iterator|float` and similar declarations for generator functions instead of requiring the whole return type to be iterable. - Added `GeneratorReturnTypeHelper::getGeneratorType()` which extracts only the iterable, non-array part of the return type. Without it, the non-iterable members (null, float, ...) collapse `getIterableKeyType()`/`getIterableValueType()` to `ErrorType`, which silently accepts every yielded key/value. - `YieldTypeRule` and `YieldFromTypeRule` use the helper so yielded key/value types (and the delegated `TSend` type) are still validated for nullable/union generator return types. - Updated `yield-in-generator.php` expectations: `\Generator|int` and `\Generator|array` are no longer reported, and added nullable/union regression cases plus a still-invalid `string|null` case.
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Summary
PHPStan reported
Yield can be used only with these return types: Generator, Iterator, Traversable, iterable.for generator functions declared with a nullable or union return type such as?Generator,\Generator|intorIterator|float. These declarations are valid PHP — a function containingyieldalways returns aGeneratorat runtime, and PHP only requires that one of the declared union members can hold it. This PR makes the generator rules treat the return type per-member instead of as a whole.Changes
src/Rules/Generators/YieldInGeneratorRule.php: flatten the declared return type viaTypeUtils::flattenTypes()and accept it when any member is iterable and not an array (i.e. can hold aGenerator), OR-combining the per-member result. Previously the whole-typeisIterable()returnedmaybefor?Generator, causing a false positive underreportMaybes.src/Rules/Generators/GeneratorReturnTypeHelper.php(new):getGeneratorType()extracts the iterable, non-array part of a return type.src/Rules/Generators/YieldTypeRule.phpandsrc/Rules/Generators/YieldFromTypeRule.php: run the declared return type throughGeneratorReturnTypeHelper::getGeneratorType()before computinggetIterableKeyType()/getIterableValueType()and the delegatedTSendtemplate type.Root cause
Two related problems, both stemming from treating a generator's declared return type as a single iterable type:
False positive in
YieldInGeneratorRule. The rule applied$returnType->isIterable()to the entire type. For a union likeGenerator|nullthis ismaybe(becausenullis not iterable), so the rule emitted an error. The correct rule — matching PHP's compiler — is that the type is valid if at least one member is iterable-and-not-array.Silent loss of yield key/value checking for nullable/union generators.
UnionType::getIterableValueType()unions the per-member iterable value types, and the non-iterable members (null,float, …) contributeErrorTypeviaNonIterableTypeTrait.TypeCombinator::union(Food, ErrorType)collapses to*ERROR*, whichaccepts()everything — soyield <wrong-type>inside a?Generator<int, Food>was never reported. The newGeneratorReturnTypeHelperstrips the non-iterable/array members first, so the realGeneratortype drives the check.Test
tests/PHPStan/Rules/Generators/data/yield-in-generator.php+YieldInGeneratorRuleTest:\Generator|intand\Generator|arrayare no longer reported; added\Generator|null,\Iterator|float,\Traversable|null,iterable|null(all valid, no error) andstring|null(still invalid, reported).tests/PHPStan/Rules/Generators/data/bug-6190.php+YieldTypeRuleTest::testBug6190: a?Generator<int, Food>and anIterator<int, Food>|floatstill report wrong yielded value/key types.tests/PHPStan/Rules/Generators/data/bug-6190-from.php+YieldFromTypeRuleTest::testBug6190:yield frominto a?Generator<int, Food>still reports a wrong delegated value type.All three regression tests were confirmed to fail before the corresponding fix and pass after.
Fixes phpstan/phpstan#6190