Fix #10698: False positive argument.type (… expects Foo<string|null>, Foo<string|null> given.)

[phpstan-bot]

Summary

Fixes a false positive argument.type error where passing a generic object with a nullable type argument (e.g., Foo<string|null>) to a parameter expecting the exact same type would report "expects Foo<string|null>, Foo<string|null> given" at rule levels 5-7 (but not at level 8+).

Changes

• Modified GenericObjectType::isSuperTypeOfInternal() in src/Type/Generic/GenericObjectType.php to handle the accepts context for invariant template type parameters: when the invariance check fails, verify whether the mismatch is only due to asymmetric null stripping by RuleLevelHelper::transformAcceptedType
• Added regression test in tests/PHPStan/Rules/Methods/data/bug-10698.php and test method in tests/PHPStan/Rules/Methods/CallMethodsRuleTest.php

Root cause

RuleLevelHelper::transformAcceptedType() uses TypeTraverser::map to strip null from union types when checkNullables is false (rule levels < 8). This traversal recurses into GenericObjectType's inner type arguments, transforming Foo<string|null> (accepted) into Foo<string>. However, the accepting type Foo<string|null> retains its null. The invariance check in TemplateTypeVariance::isValidVariance() then compares string|null (from accepting) vs string (from accepted) using equals(), which fails, producing the false positive.

The fix adds a fallback check in GenericObjectType::isSuperTypeOfInternal(): when in accepts context and the invariance check fails, it verifies whether the accepting type without null equals the accepted type (i.e., the mismatch was solely due to null stripping). If so, the result is treated as a match.

Test

Added a regression test that reproduces the exact scenario from the issue: a generic class Foo<T> passed to a method expecting Foo<T>, where the type argument is string|null. The test runs with checkNullables=false and checkUnionTypes=true (simulating level 7) and verifies no error is reported.

Fixes phpstan/phpstan#10698