Allow setting property on templated type

src/Psalm/Internal/Analyzer/Statements/Expression/Assignment/PropertyAssignmentAnalyzer.php

@@ -225,7 +225,20 @@ class PropertyAssignmentAnalyzer
 
             $has_valid_assignment_type = false;
 
-            foreach ($lhs_type->getAtomicTypes() as $lhs_type_part) {
+            $lhs_atomic_types = $lhs_type->getAtomicTypes();
+
+            while ($lhs_atomic_types) {
+                $lhs_type_part = \array_pop($lhs_atomic_types);
+
+                if ($lhs_type_part instanceof Type\Atomic\TTemplateParam) {
+                    $lhs_atomic_types = \array_merge(
+                        $lhs_atomic_types,
+                        $lhs_type_part->as->getAtomicTypes()
+                    );
+
+                    continue;
+                }
+
                 if ($lhs_type_part instanceof TNull) {
                     continue;
                 }

tests/Template/ClassTemplateTest.php

@@ -2699,6 +2699,21 @@ class ClassTemplateTest extends TestCase
                         $fn($o);
                     }'
             ],
+            'changePropertyTypeOfTemplate' => [
+                '<?php
+                    class A {
+                        public int $x = 0;
+                    }
+
+                    /**
+                     * @template T as A
+                     * @param T $obj
+                     * @param-out T $obj
+                     */
+                    function foo(A &$obj): void {
+                        $obj->x = 1;
+                    }'
+            ],
         ];
     }