Suggest symfony/yaml, and say so when a YAML specification needs it

README.md

@@ -26,6 +26,9 @@ composer require radebatz/openapi-verifier
 ```
 After that all required classes should be availabe in your project to add routing support.
 
+Some features need further packages, such as a framework adapter or YAML support. They are listed
+as suggestions, and `composer suggests radebatz/openapi-verifier` shows them.
+
 ## Usage
 ### Manual verification
 The `VerifiesOpenApi` trait can be used directly and customized in 3 ways in order to provide the reqired OpenApi specifications:

composer.json

@@ -69,6 +69,7 @@
     "suggest": {
         "laravel/laravel": "A PHP framework",
         "slim/slim": "A PHP framework",
+        "symfony/yaml": "To load YAML specifications",
         "zircote/swagger-php": "OpenApi library to generate OpenAPI documentation from PHP annotations."
     }
 }

src/OpenApiSpecificationLoader.php

@@ -23,6 +23,10 @@ protected function resolveSpecification($specification)
         $resolved = null;
         if (is_string($specification)) {
             if (false !== strpos($specification, '.yaml') || false !== strpos($specification, '.yml')) {
+                if (!class_exists(Yaml::class)) {
+                    throw new \LogicException(sprintf('Unable to load specification "%s" as symfony/yaml is not installed. Try running "composer require symfony/yaml".', $specification));
+                }
+
                 try {
                     $resolved = (object) Yaml::parseFile($specification, Yaml::PARSE_OBJECT_FOR_MAP);
                 } catch (ParseException $parseException) {