Properly derive schemas for tuples (#3954)

core/src/main/scala-2/sttp/tapir/generic/auto/SchemaMagnoliaDerivation.scala

@@ -15,7 +15,7 @@ trait SchemaMagnoliaDerivation {
 
   def join[T](ctx: ReadOnlyCaseClass[Schema, T])(implicit genericDerivationConfig: Configuration): Schema[T] = {
     withCache(ctx.typeName, ctx.annotations) {
-      val result =
+      var result =
         if (ctx.isValueClass) {
           require(ctx.parameters.nonEmpty, s"Cannot derive schema for generic value class: ${ctx.typeName.owner}")
           val valueSchema = ctx.parameters.head.typeclass
@@ -24,6 +24,9 @@ trait SchemaMagnoliaDerivation {
           // Not using inherited annotations when generating type name, we don't want @encodedName to be inherited for types
           Schema[T](schemaType = productSchemaType(ctx), name = Some(typeNameToSchemaName(ctx.typeName, ctx.annotations)))
         }
+      if (ctx.typeName.full.startsWith("scala.Tuple")) {
+        result = result.attribute(Schema.Tuple.Attribute, Schema.Tuple(true))
+      }
       enrichSchema(result, mergeAnnotations(ctx.annotations, ctx.inheritedAnnotations))
     }
   }

core/src/main/scala-3/sttp/tapir/generic/auto/SchemaMagnoliaDerivation.scala

@@ -18,7 +18,7 @@ trait SchemaMagnoliaDerivation {
 
       override def join[T](ctx: CaseClass[Schema, T]): Schema[T] = {
         withCache(ctx.typeInfo, ctx.annotations) {
-          val result =
+          var result =
             if (ctx.isValueClass) {
               require(ctx.params.nonEmpty, s"Cannot derive schema for generic value class: ${ctx.typeInfo.owner}")
               val valueSchema = ctx.params.head.typeclass
@@ -27,6 +27,9 @@ trait SchemaMagnoliaDerivation {
               // Not using inherited annotations when generating type name, we don't want @encodedName to be inherited for types
               Schema[T](schemaType = productSchemaType(ctx), name = Some(typeNameToSchemaName(ctx.typeInfo, ctx.annotations)))
             }
+          if (ctx.typeInfo.full.startsWith("scala.Tuple")) {
+            result = result.attribute(Schema.Tuple.Attribute, Schema.Tuple(true))
+          }
           enrichSchema(result, mergeAnnotations(ctx.annotations, ctx.inheritedAnnotations))
         }
       }

core/src/main/scala/sttp/tapir/Schema.scala

@@ -350,15 +350,15 @@ object Schema extends LowPrioritySchema with SchemaCompanionMacros {
     val Attribute: AttributeKey[UniqueItems] = new AttributeKey[UniqueItems]("sttp.tapir.Schema.UniqueItems")
   }
 
-  /** Hints that a [[SchemaType.SProduct]] should be rendered in the schema as an `array` (#3941).
+  /** Specifies that the given schema is for a tuple. Tuples are products with no meaningful property names - attributes are identified by
+    * their position.
     *
-    * Used to model tuples, which are products with no meaningful property names - attributes are identified by their position. When
-    * converting to JSON schema, adding this attribute on a schema for a `SProduct` renders `array` schema, with type constraints for each
-    * index.
+    * When converting a tuple schema of type [[SchemaType.SProduct]] to JSON schema, renders as an `array` schema, with type constraints for
+    * each index (#3941).
     */
-  case class ProductAsArray(productAsArray: Boolean)
-  object ProductAsArray {
-    val Attribute: AttributeKey[ProductAsArray] = new AttributeKey[ProductAsArray]("sttp.tapir.Schema.ProductAsArray")
+  case class Tuple(isTuple: Boolean)
+  object Tuple {
+    val Attribute: AttributeKey[Tuple] = new AttributeKey[Tuple]("sttp.tapir.Schema.Tuple")
   }
 
   /** @param typeParameterShortNames

docs/apispec-docs/src/main/scala/sttp/tapir/docs/apispec/schema/TSchemaToASchema.scala

@@ -33,7 +33,7 @@ private[docs] class TSchemaToASchema(
           case TSchemaType.SNumber()  => ASchema(SchemaType.Number)
           case TSchemaType.SBoolean() => ASchema(SchemaType.Boolean)
           case TSchemaType.SString()  => ASchema(SchemaType.String)
-          case TSchemaType.SProduct(fields) if schema.attribute(TSchema.ProductAsArray.Attribute).map(_.productAsArray).getOrElse(false) =>
+          case TSchemaType.SProduct(fields) if schema.attribute(TSchema.Tuple.Attribute).map(_.isTuple).getOrElse(false) =>
             ASchema(SchemaType.Array).copy(
               prefixItems = Some(fields.map(f => apply(f.schema, allowReference = true)))
             )

docs/apispec-docs/src/test/scala/sttp/tapir/docs/apispec/schema/TapirSchemaToJsonSchemaTest.scala

@@ -13,7 +13,7 @@ import sttp.tapir.Schema.annotations.title
 import sttp.tapir._
 import sttp.tapir.generic.auto._
 
-class JsonSchemasTest extends AnyFlatSpec with Matchers with OptionValues with EitherValues with Inside {
+class TapirSchemaToJsonSchemaTest extends AnyFlatSpec with Matchers with OptionValues with EitherValues with Inside {
   behavior of "TapirSchemaToJsonSchema"
 
   it should "represent schema as JSON" in {
@@ -150,9 +150,8 @@ class JsonSchemasTest extends AnyFlatSpec with Matchers with OptionValues with E
     TapirSchemaToJsonSchema(schema2, true).title shouldBe Some("Map_Either_Int_Node_Int_String")
   }
 
-  it should "Generate array for products marked with ProductAsArray attribute" in {
+  it should "Generate array for products marked with Tuple attribute" in {
     val tSchema: Schema[(Int, String)] = implicitly[Schema[(Int, String)]]
-      .attribute(Schema.ProductAsArray.Attribute, Schema.ProductAsArray(true))
 
     // when
     val result = TapirSchemaToJsonSchema(tSchema, markOptionsAsNullable = false)