Fix phpstan/phpstan#12244: $this(Type~Subtracted) does not work on conditional return type as Type~Subtracted

src/Type/StaticType.php

@@ -369,6 +369,13 @@ private function transformStaticType(Type $type, ClassMemberAccessAnswerer $scop
 					$type = new self($type->getClassReflection(), $type->getSubtractedType());
 				}
 
+				if ($this->getSubtractedType() !== null) {
+					$type = $type->subtract($this->getSubtractedType());
+					if (!$type instanceof StaticType) {
+						return $traverse($type);
+					}
+				}
+
 				if (!$isFinal || $type instanceof ThisType) {
 					return $traverse($type);
 				}

tests/PHPStan/Analyser/nsrt/bug-12244.php

@@ -0,0 +1,77 @@
+<?php // lint >= 8.1
+
+declare(strict_types = 1);
+
+namespace Bug12244;
+
+use function PHPStan\Testing\assertType;
+
+enum X: string {
+	case A = 'a';
+	case B = 'b';
+	case C = 'c';
+
+	/** @return ($this is self::A ? int : null) */
+	public function get(): ?int {
+		return ($this === self::A) ? 123 : null;
+	}
+
+	public function doSomething(): void {
+		if ($this !== self::A) {
+			assertType('$this(Bug12244\X~Bug12244\X::A)', $this);
+			assertType('null', $this->get());
+		} else {
+			assertType('int', $this->get());
+		}
+
+		if ($this !== self::B && $this !== self::C) {
+			assertType('int', $this->get());
+		}
+	}
+
+	public static function doSomethingFor(X $x): void {
+		if ($x !== self::A) {
+			assertType('Bug12244\X~Bug12244\X::A', $x);
+			assertType('null', $x->get());
+		} else {
+			assertType('int', $x->get());
+		}
+
+		if ($x !== self::B && $x !== self::C) {
+			assertType('int', $x->get());
+		}
+	}
+}
+
+enum Y: string {
+	case A = 'a';
+	case B = 'b';
+	case C = 'c';
+
+	/** @param-out ($this is self::A ? int : null) $i */
+	public function get(?int &$i): void {
+		($this === self::A) ? $i=null : $i=123;
+	}
+
+	public function doSomething(): void {
+		$i = 0;
+		if ($this !== self::A) {
+			$this->get($i);
+			assertType('null', $i); // null
+		} else {
+			$this->get($i);
+			assertType('int', $i); // int
+		}
+	}
+
+	public static function doSomethingFor(Y $x): void {
+		$i = 0;
+		if ($x !== self::A) {
+			$x->get($i);
+			assertType('null', $i); // null
+		} else {
+			$x->get($i);
+			assertType('int', $i); // int
+		}
+	}
+}