Fix phpstan/phpstan#14413: Narrowing generic union via ::class comparison discards type parameters

[phpstan-bot]

Summary

When narrowing a generic union type like Cat<string>|Dog<string> via $a::class === Cat::class, PHPStan was discarding the generic type parameters. The narrowed type became Cat&Cat<string> (a redundant intersection) instead of Cat<string>.

Changes

• Modified src/Analyser/TypeSpecifier.php:
  • Added determineExactClassType() helper method that intersects the expression's current scope type with a plain ObjectType to extract generic parameters, then returns the narrowed type if it's more specific, or falls back to ObjectType with asFinal()
  • Updated 3 call sites: get_class($a) === 'Foo', $a::class === 'Foo', and 'Foo' === $a::class to use the new helper
• Added tests/PHPStan/Analyser/nsrt/bug-14413.php regression test

Root cause

Commit 772f297 introduced asFinal() on the ObjectType created for ::class/get_class() narrowing to prevent subclass matches. However, ObjectType('Cat', asFinal).isSuperTypeOf(GenericObjectType('Cat', [StringType])) returns Maybe (because hasFinalByKeywordOverride is true on ObjectType but false on GenericObjectType). This prevented TypeCombinator::intersect from simplifying the intersection, leaving both Cat and Cat<string> in the result as Cat&Cat<string>.

The fix pre-narrows the expression type by intersecting with a plain ObjectType (which correctly simplifies generics), then checks if the result is more specific. If it has generic parameters, it uses the narrowed type directly. For non-generic cases, it falls back to the asFinal() behavior.

Test

Added tests/PHPStan/Analyser/nsrt/bug-14413.php covering:

• match expression with $a::class preserving generic parameters
• if/else with $a::class === preserving generic parameters
• Mirror case Cat::class === $a::class
• match with method call using generic return type
• Non-matching class narrowing to *NEVER*

Fixes phpstan/phpstan#14413