Fix phpstan/phpstan#13247: iterable is equal to array|Traversable

[phpstan-bot]

Summary

iterable<K, V> is semantically equivalent to array<K, V>|Traversable<K, V>, but PHPStan was not accepting iterable<K, V> as an argument where array<K, V>|Traversable<K, V> was expected. This caused false positive argument.type errors and failed template type resolution (argument.templateType errors).

Changes

• src/Type/UnionType.php: Added iterable-to-union decomposition in two methods:
  • accepts(): Converts IterableType<K,V> to UnionType([ArrayType<K,V>, GenericObjectType(Traversable, [K,V])]) before checking acceptance, so that iterable<K,V> is properly accepted by array<K,V>|Traversable<K,V>
  • inferTemplateTypes(): Same decomposition so template type parameters (K, V) are correctly inferred from an iterable argument when the parameter type is a union of array and Traversable
• phpstan-baseline.neon: Updated instanceof IterableType ignore count from 1 to 3 for UnionType.php
• tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php: Added testBug13247 test method
• tests/PHPStan/Rules/Functions/data/bug-13247.php: Regression test data file

Root cause

UnionType::inferTemplateTypes() iterates through each union member and calls inferTemplateTypes() on them. When the received type was IterableType, neither ArrayType::inferTemplateTypes() (which requires isArray()->yes()) nor GenericObjectType::inferTemplateTypes() could extract template information from it, resulting in empty template maps. Similarly, UnionType::accepts() checked each union member individually, none of which could fully accept the iterable type, and the fallback via IterableType::isAcceptedBy() → isSubTypeOf() decomposed to a form that didn't match properly against generic Traversable types.

The fix decomposes IterableType<K,V> into its equivalent array<K,V>|Traversable<K,V> union at the start of both methods, allowing the existing union-handling logic to process it correctly.

Test

Added a regression test that defines a function accepting array<K,V>|Traversable<K,V> and another function that passes iterable<K,V> to it. The test expects no errors, confirming that the iterable type is correctly accepted and templates are properly resolved.

Fixes phpstan/phpstan#13247