Fix common prefix computation so it only goes up to the last backslash

Author: gvlasov

src/Structures/NamespacedType.php

@@ -34,7 +34,10 @@ public static function commonPrefix(string $a, string $b): string {
             $i++;
         }
 
-        return substr($a, 0, $i);
+        $prefix = substr($a, 0, $i);
+        $lastSlashPos = strrpos($prefix, '\\');
+
+        return $lastSlashPos !== false ? substr($prefix, 0, $lastSlashPos + 1) : '';
     }
 
     public static function shortName(string|ReflectionClass $type): string {

tests/Structures/NamespacedTypeTest.php

@@ -21,3 +21,19 @@
         )
     );
 });
+it('common prefix goes up to last backslash even with another nesting level', function () {
+    assertEquals(
+        'app\\', // not 'app\\co'
+        NamespacedType::commonPrefix(
+            'app\\companies',
+            'app\\countries'
+        )
+    );
+    assertEquals(
+        'app\\',
+        NamespacedType::commonPrefix(
+            'app\\data',
+            'app\\data\\stuff'
+        )
+    );
+});