Restore support for shorthand nullable compounds

While PHP types do not support shorthand nullable syntax in compound
types (e.g. `?string|int`), it has been requested to retain support
for this in phpdoc types for backwards compatibility reasons.

Author: hemberger

src/TypeResolver.php

@@ -210,6 +210,7 @@ private function parseTypes(ArrayIterator $tokens, Context $context, int $parser
                         self::PARSER_IN_COMPOUND,
                         self::PARSER_IN_ARRAY_EXPRESSION,
                         self::PARSER_IN_COLLECTION_EXPRESSION,
+                        self::PARSER_IN_NULLABLE,
                     ], true)
                 ) {
                     throw new RuntimeException(
@@ -225,6 +226,7 @@ private function parseTypes(ArrayIterator $tokens, Context $context, int $parser
                         self::PARSER_IN_COMPOUND,
                         self::PARSER_IN_ARRAY_EXPRESSION,
                         self::PARSER_IN_COLLECTION_EXPRESSION,
+                        self::PARSER_IN_NULLABLE,
                     ], true)
                 ) {
                     throw new RuntimeException(

tests/unit/TypeResolverTest.php

@@ -407,9 +407,11 @@ public function testResolvingNullableCompoundTypes(): void
     {
         $fixture = new TypeResolver();
 
-        $this->expectException('RuntimeException');
-        $this->expectExceptionMessage('Unexpected type separator');
+        // Note that in PHP types it is illegal to use shorthand nullable
+        // syntax with unions. This would be 'string|boolean|null' instead.
         $resolvedType = $fixture->resolve('?string|null|?boolean');
+
+        $this->assertSame('?string|null|?bool', (string) $resolvedType);
     }
 
     /**