Fix phpstan/phpstan#9732: BenevolentUnionType with generics produce confusing errors

[phpstan-bot]

Summary

When passing $GLOBALS (which has a BenevolentUnionType(int|string) key type) to a function expecting array<TKeyType of string, TValueType>, PHPStan incorrectly reported two false positive errors:

1. "Unable to resolve the template type TKeyType" (argument.templateType)
2. "Parameter expects array<string, mixed>, array given" (argument.type)

Changes

• src/Type/ArrayType.php: Changed the StrictMixedType key normalization in the constructor to produce BenevolentUnionType instead of regular UnionType. This preserves benevolent semantics when RuleLevelHelper::transformAcceptedType() traverses array types and converts implicit MixedType to StrictMixedType.
• src/Type/Generic/TemplateTypeTrait.php: Added handling for BenevolentUnionType in inferTemplateTypes(). When the received type is a benevolent union that doesn't fully satisfy the template bound, we filter to only the inner types that match the bound and use those for template resolution.
• tests/PHPStan/Rules/Methods/CallStaticMethodsRuleTest.php: Added testBug9732 test method.
• tests/PHPStan/Rules/Methods/data/bug-9732.php: Added regression test data file.

Root cause

Two separate issues combined to produce the false positives:

Issue 1 (argument.type): The ArrayType constructor normalizes BenevolentUnionType(int, string) keys to MixedType for storage, and getIterableKeyType() reconstructs them. However, during RuleLevelHelper::transformAcceptedType(), the transformCommonType traversal converts the stored MixedType key to StrictMixedType (when checkImplicitMixed is true). When ArrayType::traverse creates a new ArrayType with the StrictMixedType key, the constructor was converting it to a regular UnionType([StringType, IntegerType]) instead of BenevolentUnionType. This caused the accepts() check to fail because a regular UnionType(int, string) is not fully accepted by StringType when checkForUnion is true.

Issue 2 (argument.templateType): TemplateTypeTrait::inferTemplateTypes() checks if the template bound (string) is a supertype of the received type (BenevolentUnionType(int, string)). Since StringType->isSuperTypeOf(BenevolentUnionType(int, string)) returns Maybe (not Yes), the template type was not resolved. The fix filters the benevolent union to only the types matching the bound (string in this case) and uses the filtered type for template resolution.

Test

Added regression test testBug9732 in CallStaticMethodsRuleTest that passes $GLOBALS to a static method with template types TKeyType of string and TValueType, expecting no errors.

Fixes phpstan/phpstan#9732

[staabm]

can we drop the previous if on line 285 than? seems like its redundant now?

[VincentLanglet]

It's not redundant, the previous if will works

• For any non UnionType
• For BenevolentUnionType
• For UnionType in which the whole type is superTypeOf