Fix generic type inference for new assigned to property via ??=

- Added handling for AssignOp\Coalesce in NewAssignedToPropertyVisitor
- The visitor now marks `new` expressions in `$this->prop ??= new Foo()` with the property attribute, so MutatingScope::exactInstantiation() can infer generic type parameters from the property's declared type
- New regression test in tests/PHPStan/Rules/Properties/data/bug-12250.php

Closes phpstan/phpstan#12250

Author: phpstan-bot

src/Parser/NewAssignedToPropertyVisitor.php

@@ -16,7 +16,7 @@ final class NewAssignedToPropertyVisitor extends NodeVisitorAbstract
 	#[Override]
 	public function enterNode(Node $node): ?Node
 	{
-		if ($node instanceof Node\Expr\Assign || $node instanceof Node\Expr\AssignRef) {
+		if ($node instanceof Node\Expr\Assign || $node instanceof Node\Expr\AssignRef || $node instanceof Node\Expr\AssignOp\Coalesce) {
 			if (
 				($node->var instanceof Node\Expr\PropertyFetch || $node->var instanceof Node\Expr\StaticPropertyFetch)
 				&& $node->expr instanceof Node\Expr\New_

tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php

@@ -1003,4 +1003,10 @@ public function testCloneWith(): void
 		]);
 	}
 
+	#[RequiresPhp('>= 8.0')]
+	public function testBug12250(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-12250.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Properties/data/bug-12250.php

@@ -0,0 +1,17 @@
+<?php // lint >= 8.0
+
+namespace Bug12250;
+
+class HelloWorld
+{
+	/**
+	 * @var \WeakMap<\stdClass, \stdClass>
+	 */
+	protected \WeakMap $bug, $ok;
+
+	public function bug(): void
+	{
+		$this->bug ??= new \WeakMap();
+		$this->ok = new \WeakMap();
+	}
+}