Fix phpstan/phpstan#14102: No error if construct signature of class-string of abstract class is invalid

[phpstan-bot]

Summary

When using class-string<AbstractClass> with new $className(), PHPStan was not checking constructor parameters if the class was abstract. This fix ensures constructor parameter validation works for abstract classes resolved from class-string types.

Changes

• Modified src/Rules/Classes/InstantiationRule.php:
  • Removed !$classReflection->isAbstract() from the filter in getClassNames() so abstract classes from class-string types are included in constructor validation
  • Added $isFromClassString flag (third element in the return tuple) to distinguish class-string-resolved names from constant string or direct names
  • Skip class-string resolution when the type has constant strings (e.g. Foo::class), so those still correctly report "abstract class" errors via the existing path
  • Used $isFromClassString flag in checkClassName() to suppress the "Instantiated class X is abstract" error for class-string-resolved types
• Updated tests/PHPStan/Rules/Classes/InstantiationRuleTest.php:
  • Added testBug14102() regression test
  • Updated testClassString() to expect constructor parameter errors for abstract class B
• Added tests/PHPStan/Rules/Classes/data/bug-14102.php test data

Root cause

In InstantiationRule::getClassNames(), abstract classes were explicitly filtered out when resolving class-string types. This was overly conservative — while you can't directly instantiate an abstract class, class-string<AbstractClass> represents concrete subclasses that inherit the abstract class's constructor signature. The constructor parameters should still be validated.

The fix includes abstract classes in the class-string resolution but introduces a $isFromClassString flag to prevent false "Instantiated class X is abstract" errors. Constant string types (Foo::class) are excluded from the class-string path so they continue to correctly report abstract instantiation errors.

Test

Added tests/PHPStan/Rules/Classes/data/bug-14102.php which reproduces the exact scenario from the issue: an abstract class HelloWorld with a 2-parameter constructor, and a factory method accepting class-string<HelloWorld> that calls new $className() with 0 parameters. The test expects the error "Class Bug14102\HelloWorld constructor invoked with 0 parameters, 2 required."

Fixes phpstan/phpstan#14102

[ondrejmirtes]

This is a new class of error that should only be there with bleeding edge