Setting array offset on a property should pick types from original UnionType still present in the current property type

Author: ondrejmirtes

src/Analyser/MutatingScope.php

@@ -778,13 +778,29 @@ public function getType(Expr $node): Type
 			return $this->getType($node->getVar())->unsetOffset($this->getType($node->getDim()));
 		}
 		if ($node instanceof SetOffsetValueTypeExpr) {
-			return $this->getType($node->getVar())->setOffsetValueType(
+			$varNode = $node->getVar();
+			$varType = $this->getType($varNode);
+			if ($varNode instanceof OriginalPropertyTypeExpr) {
+				$currentPropertyType = $this->getType($varNode->getPropertyFetch());
+				if ($varType instanceof UnionType) {
+					$varType = $varType->filterTypes(static fn (Type $innerType) => !$innerType->isSuperTypeOf($currentPropertyType)->no());
+				}
+			}
+			return $varType->setOffsetValueType(
 				$node->getDim() !== null ? $this->getType($node->getDim()) : null,
 				$this->getType($node->getValue()),
 			);
 		}
 		if ($node instanceof SetExistingOffsetValueTypeExpr) {
-			return $this->getType($node->getVar())->setExistingOffsetValueType(
+			$varNode = $node->getVar();
+			$varType = $this->getType($varNode);
+			if ($varNode instanceof OriginalPropertyTypeExpr) {
+				$currentPropertyType = $this->getType($varNode->getPropertyFetch());
+				if ($varType instanceof UnionType) {
+					$varType = $varType->filterTypes(static fn (Type $innerType) => !$innerType->isSuperTypeOf($currentPropertyType)->no());
+				}
+			}
+			return $varType->setExistingOffsetValueType(
 				$this->getType($node->getDim()),
 				$this->getType($node->getValue()),
 			);

tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php

@@ -942,4 +942,11 @@ public function testBug13035(): void
 		$this->analyse([__DIR__ . '/data/bug-13035.php'], []);
 	}
 
+	public function testBug13654(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->checkImplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/bug-13654.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Properties/data/bug-13654.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace Bug13654;
+
+/**
+ * @phpstan-type TType array{
+ *    text: string,
+ *	  missing: string,
+ * }
+ */
+class HelloWorld
+{
+	/**
+	 * @var TType|null
+	 */
+	private ?array $test = null;
+
+	/**
+	 * @param TType $test
+	 */
+	public function setTest(array $test): void
+	{
+		$this->test = $test;
+	}
+
+	/**
+	 * @return TType
+	 */
+	public function modify(): array
+	{
+		if ($this->test === null) {
+			throw new \Exception();
+		}
+
+		$this->test['text'] = 'asdsdsd';
+
+		return $this->test;
+	}
+}