Fix phpstan/phpstan#10076: Union of string literal and class-string<T> does not accept that string

[phpstan-bot]

Summary

When a parameter has type 'object'|'array'|class-string<T>, passing 'object' or 'array' should be accepted because they match the string literal parts of the union. Instead, PHPStan reported false positive errors like "expects class-string, string given" because the literal string members were silently absorbed into class-string<T> during type construction.

Changes

• Fixed GenericClassStringType::isSuperTypeOf() in src/Type/Generic/GenericClassStringType.php to return Maybe instead of Yes when the generic type is MixedType (which includes TemplateMixedType) and the constant string is not a valid class-string
• Added regression test in tests/PHPStan/Rules/Functions/data/bug-10076.php and test method in tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php

Root cause

GenericClassStringType::isSuperTypeOf() had a fast path: when the generic type was instanceof MixedType, it unconditionally returned Yes for any ConstantStringType. Template types with no explicit bound are TemplateMixedType (which extends MixedType), so class-string<T> claimed to be a supertype of strings like 'object' and 'array'. This caused TypeCombinator::union to absorb the constant string members, collapsing 'object'|'array'|class-string<T> into just class-string<T>. After template resolution, the parameter type became class-string<object> instead of 'object'|'array'|class-string<object>, producing false positive argument type errors.

The fix adds a guard: non-class-string constants now get Maybe instead of Yes, preserving them as separate union members.

Test

Added tests/PHPStan/Rules/Functions/data/bug-10076.php which reproduces the exact scenario from the issue: a function with @param 'object'|'array'|class-string<T> $type called with 'object', 'array', and DateTime::class. No errors should be reported.

Fixes phpstan/phpstan#10076