[TypeInfo] Fix PHPDoc resolving of union with mixed

Author: mtarld

src/Symfony/Component/TypeInfo/Tests/TypeResolver/StringTypeResolverTest.php

@@ -155,6 +155,8 @@ public static function resolveDataProvider(): iterable
 
         // union
         yield [Type::union(Type::int(), Type::string()), 'int|string'];
+        yield [Type::mixed(), 'int|mixed'];
+        yield [Type::mixed(), 'mixed|int'];
 
         // intersection
         yield [Type::intersection(Type::object(\DateTime::class), Type::object(\Stringable::class)), \DateTime::class.'&'.\Stringable::class];

src/Symfony/Component/TypeInfo/TypeResolver/StringTypeResolver.php

@@ -223,7 +223,19 @@ private function getTypeFromNode(TypeNode $node, ?TypeContext $typeContext): Typ
         }
 
         if ($node instanceof UnionTypeNode) {
-            return Type::union(...array_map(fn (TypeNode $t): Type => $this->getTypeFromNode($t, $typeContext), $node->types));
+            $types = [];
+
+            foreach ($node->types as $nodeType) {
+                $type = $this->getTypeFromNode($nodeType, $typeContext);
+
+                if ($type instanceof BuiltinType && TypeIdentifier::MIXED === $type->getTypeIdentifier()) {
+                    return Type::mixed();
+                }
+
+                $types[] = $type;
+            }
+
+            return Type::union(...$types);
         }
 
         if ($node instanceof IntersectionTypeNode) {