add support for discriminated union conversion to openapi (#86)

* add support for discriminated unions to openapi
* create missing headers
* rename union test operation
* remove incorrect union shape
* fix json tests
* Add discriminator field to alternatives in openapi

Co-authored-by: Olivier Mélois <[email protected]>

modules/json/test/src/smithy4s/http/json/SchematicJCodecTests.scala

@@ -195,7 +195,6 @@ object SchematicJCodecTests extends SimpleIOSuite {
 
     expect(
       result == PayloadData(
-        None,
         Some(TestBiggerUnion.OneCase(One(Some("hello"))))
       )
     )

modules/openapi/src/smithy4s/openapi/DiscriminatedUnion.scala

@@ -0,0 +1,83 @@
+/*
+ *  Copyright 2021 Disney Streaming
+ *
+ *  Licensed under the Tomorrow Open Source Technology License, Version 1.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *     https://disneystreaming.github.io/TOST-1.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package smithy4s.openapi
+
+import _root_.software.amazon.smithy.jsonschema.JsonSchemaConfig
+import _root_.software.amazon.smithy.jsonschema.JsonSchemaMapper
+import _root_.software.amazon.smithy.jsonschema.Schema.Builder
+import _root_.software.amazon.smithy.model.shapes.Shape
+
+import scala.jdk.CollectionConverters._
+import software.amazon.smithy.model.node.ObjectNode
+import smithy4s.api.DiscriminatedUnionTrait
+import software.amazon.smithy.jsonschema.Schema
+
+class DiscriminatedUnions() extends JsonSchemaMapper {
+  private final val COMPONENTS = "components"
+
+  def updateSchema(
+      shape: Shape,
+      schemaBuilder: Builder,
+      config: JsonSchemaConfig
+  ): Builder = {
+    val maybeDiscriminated = shape.getTrait(classOf[DiscriminatedUnionTrait])
+    if (maybeDiscriminated.isPresent()) {
+      val discriminated = maybeDiscriminated.get()
+      val discriminatorField = discriminated.getValue()
+      val unionSchema = schemaBuilder.build()
+
+      val alternatives = unionSchema.getOneOf().asScala
+      val discriminatedAlts =
+        alternatives.flatMap(alt => alt.getProperties().asScala)
+
+      val transformedAlts = discriminatedAlts.map { case (label, altSchema) =>
+        val localDiscriminator = Schema
+          .builder()
+          .`type`("string")
+          .enumValues(List(label).asJava)
+          .build()
+        val discObject = Schema
+          .builder()
+          .`type`("object")
+          .properties(
+            Map(
+              discriminatorField -> localDiscriminator
+            ).asJava
+          )
+          .required(List(discriminatorField).asJava)
+          .build()
+        Schema
+          .builder()
+          .allOf(
+            List(altSchema, discObject).asJava
+          )
+          .build()
+      }.asJava
+
+      schemaBuilder
+        .oneOf(transformedAlts)
+        .putExtension(
+          "discriminator",
+          ObjectNode
+            .builder()
+            .withMember("propertyName", discriminated.getValue())
+            .build()
+        )
+
+    } else schemaBuilder
+  }
+}

modules/openapi/src/smithy4s/openapi/Smithy4sOpenApiExtension.scala

@@ -44,7 +44,8 @@ final class Smithy4sOpenApiExtension() extends Smithy2OpenApiExtension {
   ).asJava
 
   override def getJsonSchemaMappers(): ju.List[JsonSchemaMapper] = List(
-    new OpenApiJsonSchemaMapper(): JsonSchemaMapper
+    new OpenApiJsonSchemaMapper(): JsonSchemaMapper,
+    new DiscriminatedUnions()
   ).asJava
 
 }