[attributes] add support for class constants

src/Analysers/AttributeAnnotationFactory.php

@@ -74,6 +74,21 @@ public function build(\Reflector $reflector, Context $context): array
                     }
                 }
             }
+
+            if ($reflector instanceof \ReflectionClass) {
+                foreach ($reflector->getReflectionConstants() as $rc) {
+                    foreach ($rc->getAttributes(Property::class) as $attribute) {
+                        $instance = $attribute->newInstance();
+                        if (Generator::isDefault($instance->property)) {
+                            $instance->property = $rc->getName();
+                        }
+                        if (Generator::isDefault($instance->type)) {
+                            $instance->const = $rc->getValue();
+                        }
+                        $annotations[] = $instance;
+                    }
+                }
+            }
         } finally {
             Generator::$context = null;
         }

src/Annotations/Schema.php

@@ -336,6 +336,8 @@ class Schema extends AbstractAnnotation
 
     /**
      * http://json-schema.org/latest/json-schema-validation.html#rfc.section.6.24.
+     *
+     * @var string
      */
     public $const = Generator::UNDEFINED;
 
@@ -362,6 +364,7 @@ class Schema extends AbstractAnnotation
         'allOf' => '[' . Schema::class . ']',
         'oneOf' => '[' . Schema::class . ']',
         'anyOf' => '[' . Schema::class . ']',
+        'const' => 'string',
     ];
 
     /**

src/Attributes/Property.php

@@ -8,7 +8,7 @@
 
 use OpenApi\Generator;
 
-#[\Attribute(\Attribute::TARGET_METHOD | \Attribute::TARGET_PROPERTY | \Attribute::TARGET_PARAMETER)]
+#[\Attribute(\Attribute::TARGET_METHOD | \Attribute::TARGET_PROPERTY | \Attribute::TARGET_PARAMETER | \Attribute::TARGET_CLASS_CONSTANT)]
 class Property extends \OpenApi\Annotations\Property
 {
     /**

src/Attributes/Schema.php

@@ -40,6 +40,7 @@ public function __construct(
         ?int $minItems = null,
         ?bool $uniqueItems = null,
         ?string $pattern = null,
+        ?string $const = null,
         ?array $enum = null,
         ?Discriminator $discriminator = null,
         ?bool $readOnly = null,
@@ -78,6 +79,7 @@ public function __construct(
             'minItems' => $minItems ?? Generator::UNDEFINED,
             'uniqueItems' => $uniqueItems ?? Generator::UNDEFINED,
             'pattern' => $pattern ?? Generator::UNDEFINED,
+            'const' => $const ?? Generator::UNDEFINED,
             'enum' => $enum ?? Generator::UNDEFINED,
             'readOnly' => $readOnly ?? Generator::UNDEFINED,
             'writeOnly' => $writeOnly ?? Generator::UNDEFINED,

src/Generator.php

@@ -191,6 +191,7 @@ public function getProcessors(): array
                 new Processors\MergeXmlContent(),
                 new Processors\OperationId(),
                 new Processors\CleanUnmerged(),
+                new Processors\BackportConstants(),
             ];
         }
 

src/Processors/BackportConstants.php

@@ -0,0 +1,36 @@
+<?php declare(strict_types=1);
+
+/**
+ * @license Apache 2.0
+ */
+
+namespace OpenApi\Processors;
+
+use OpenApi\Analysis;
+use OpenApi\Annotations\OpenApi;
+use OpenApi\Annotations\Property as AnnotationSchema;
+use OpenApi\Attributes\Property as AttributeSchema;
+use OpenApi\Generator;
+
+/**
+ * Transform const keywords to enum in OpenApi versions < 3.1.0.
+ */
+class BackportConstants
+{
+    public function __invoke(Analysis $analysis)
+    {
+        /** @var AnnotationSchema[] $schemas */
+        $schemas = $analysis->getAnnotationsOfType([AnnotationSchema::class, AttributeSchema::class], true);
+
+        foreach ($schemas as $schema) {
+            if (Generator::isDefault($schema->const)) {
+                continue;
+            }
+
+            if (version_compare($analysis->context->version, OpenApi::VERSION_3_1_0, '<')) {
+                $schema->enum = [$schema->const];
+                $schema->const = Generator::UNDEFINED;
+            }
+        }
+    }
+}