Add props annotation

modules/generic/src/main/scala-2/vulcan/generic/package.scala

@@ -89,6 +89,12 @@ package object generic {
                       case AvroName(newName) => newName
                     }
 
+                def getProps =
+                  param.annotations
+                    .collectFirst {
+                      case AvroProps(props) => props
+                    }
+
                 implicit val codec = param.typeclass
 
                 f(
@@ -101,7 +107,8 @@ package object generic {
                     if (codec.schema.exists(_.isNullable) && nullDefaultField)
                       Some(None.asInstanceOf[param.PType]) // TODO: remove cast
                     else None
-                  )
+                  ),
+                  props = getProps.getOrElse(Props.empty)
                 ).widen
               }
               .map(caseClass.rawConstruct(_))

modules/generic/src/main/scala/vulcan/generic/AvroProps.scala

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2019-2024 OVO Energy Limited
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package vulcan.generic
+
+import vulcan.Props
+import scala.annotation.StaticAnnotation
+
+/**
+  * Annotation which can be used to alter props
+  * in derived schemas.
+  *
+  * The annotation can be used in the following situations.<br>
+  * - Annotate a type for enum props when using
+  *   [[deriveEnum]].<br>
+  * - Annotate a type for fixed props when using
+  *   [[deriveFixed]].<br>
+  * - Annotate a `case class` for record props
+  *   when using `Codec.derive` from the generic module.<br>
+  * - Annotate a `case class` parameter for record field
+  *   props when using `Codec.derive` from the
+  *   generic module.
+  */
+final class AvroProps(final val prop: Props) extends StaticAnnotation {
+  override final def toString: String =
+    s"AvroProps($prop)"
+}
+
+private[vulcan] object AvroProps {
+  final def unapply(avroProps: AvroProps): Some[Props] =
+    Some(avroProps.prop)
+}

modules/generic/src/test/scala/vulcan/generic/AvroPropsSpec.scala

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2019-2024 OVO Energy Limited
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package vulcan.generic
+
+import vulcan.{BaseSpec, Props}
+final class AvroPropsSpec extends BaseSpec {
+  describe("AvroProps") {
+    it("should provide props via props") {
+      forAll { (name: String, value: String) =>
+        assert(new AvroProps(Props.one(name, value)).prop.toChain == Props.one(name, value).toChain)
+      }
+    }
+
+    it("should include name and value in props toString") {
+      forAll { (name: String, value: String) =>
+        val propsString = new AvroProps(Props.one(name, value)).toString
+        assert(propsString.contains(name) && propsString.contains(value))
+      }
+    }
+
+    it("should provide an extractor for props") {
+      forAll { (name: String, value: String) =>
+        assert(new AvroProps(Props.one(name, value)) match {
+          case AvroProps(props) =>
+            props.toChain.toOption.exists(_.exists { case (n, _) => n == name })
+          case _ => false
+        })
+      }
+    }
+  }
+}

modules/generic/src/test/scala/vulcan/generic/GenericDerivationCodecSpec.scala

@@ -47,6 +47,12 @@ final class GenericDerivationCodecSpec extends CodecBase {
             }
           }
 
+          it("should support annotation for props") {
+            assertSchemaIs[CaseClassAvroProps] {
+              """{"type":"record","name":"CaseClassAvroProps","namespace":"vulcan.generic.examples","fields":[{"name":"value","type":["null","string"],"prop1":"A","prop2":"B"}]}"""
+            }
+          }
+
           it("should capture errors on invalid names") {
             assertSchemaError[CaseClassFieldInvalidName] {
               """org.apache.avro.SchemaParseException: Illegal initial character: -value"""

modules/generic/src/test/scala/vulcan/generic/examples/CaseClassAvroProps.scala

@@ -0,0 +1,15 @@
+package vulcan.generic.examples
+
+import vulcan.{Codec, Props}
+import vulcan.generic._
+
+@AvroName("CaseClassAvroProps")
+final case class CaseClassAvroProps(
+  @AvroName("value")
+  @AvroProps(Props.one("prop1", "A").add("prop2", "B"))
+  value: Option[String]
+)
+
+object CaseClassAvroProps {
+  implicit val codec: Codec[CaseClassAvroProps] = Codec.derive
+}