Summary

When passing an iterable<K, V> to a function expecting array<K, V>|Traversable<K, V>, PHPStan incorrectly reported a type error and failed to resolve template types, even though iterable<K, V> is semantically equivalent to array<K, V>|Traversable<K, V>.

Changes

• src/Type/IterableType.php: Changed isSubTypeOf() to decompose iterable<K,V> into array<K,V> | Traversable<K,V> (using GenericObjectType) instead of array<K,V> | (ObjectType(Traversable) & iterable<K,V>). The old intersection-based decomposition lost generic type information because the unparameterized ObjectType(Traversable) couldn't match against GenericObjectType(Traversable<K,V>).
• src/Type/UnionType.php: Added early decomposition of IterableType in inferTemplateTypes() — when the received type is iterable<K,V>, it is decomposed into array<K,V> | Traversable<K,V> before template inference, allowing each union member to correctly infer template types from its matching component.
• phpstan-baseline.neon: Updated instanceof IterableType ignore count from 1 to 2 for UnionType.php.
• tests/PHPStan/Rules/Functions/data/bug-13247.php: New regression test data file.
• tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php: Added testBug13247().

Root cause

Two separate issues caused the bug:

1. Template inference failure: UnionType::inferTemplateTypes() tried to infer template types by delegating to each union member (ArrayType and GenericObjectType(Traversable)). Neither could infer templates from an IterableType — ArrayType::inferTemplateTypes rejects non-array types, and GenericObjectType::inferTemplateTypes requires TypeWithClassName. With templates unresolved, the parameter type fell back to template bounds.

2. Subtype check failure: IterableType::isSubTypeOf() decomposed iterable<K,V> into array<K,V> | (ObjectType(Traversable) & iterable<K,V>). The intersection used an unparameterized ObjectType(Traversable), which couldn't properly match against GenericObjectType(Traversable<K,V>) in the target union, causing the subtype check to fail.

Test

Added a regression test testBug13247 that verifies passing iterable<K, V> to a function expecting array<K, V>|Traversable<K, V> produces no errors.

Fixes phpstan/phpstan#13247