Adds returns function to ResolverDSL to allow generic queries

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/dsl/DataLoaderPropertyDSL.kt

@@ -88,4 +88,8 @@ class DataLoaderPropertyDSL<T, K, R>(
         this.inputValues.addAll(inputValues)
     }
 
+    override fun setReturnType(type: KType) {
+        // NOOP
+    }
+
 }

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/dsl/PropertyDSL.kt

@@ -5,6 +5,7 @@ import com.apurebase.kgraphql.schema.model.FunctionWrapper
 import com.apurebase.kgraphql.schema.model.InputValueDef
 import com.apurebase.kgraphql.schema.model.PropertyDef
 import java.lang.IllegalArgumentException
+import kotlin.reflect.KType
 
 
 class PropertyDSL<T : Any, R>(val name : String, block : PropertyDSL<T, R>.() -> Unit) : LimitedAccessItemDSL<T>(), ResolverDSL.Target {
@@ -62,4 +63,8 @@ class PropertyDSL<T : Any, R>(val name : String, block : PropertyDSL<T, R>.() ->
     override fun addInputValues(inputValues: Collection<InputValueDef<*>>) {
         this.inputValues.addAll(inputValues)
     }
+
+    override fun setReturnType(type: KType) {
+        // NOOP
+    }
 }

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/dsl/ResolverDSL.kt

@@ -2,9 +2,10 @@ package com.apurebase.kgraphql.schema.dsl
 
 import com.apurebase.kgraphql.schema.dsl.types.InputValuesDSL
 import com.apurebase.kgraphql.schema.model.InputValueDef
+import kotlin.reflect.*
 
 
-class ResolverDSL(private val target: Target) {
+class ResolverDSL(val target: Target) {
     fun withArgs(block : InputValuesDSL.() -> Unit){
         val inputValuesDSL = InputValuesDSL().apply(block)
 
@@ -13,7 +14,14 @@ class ResolverDSL(private val target: Target) {
         })
     }
 
+    @OptIn(ExperimentalStdlibApi::class)
+    inline fun <reified T: Any> returns(): ResolverDSL {
+        target.setReturnType(typeOf<T>())
+        return this
+    }
+
     interface Target {
         fun addInputValues(inputValues: Collection<InputValueDef<*>>)
+        fun setReturnType(type: KType)
     }
 }

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/dsl/UnionPropertyDSL.kt

@@ -6,6 +6,7 @@ import com.apurebase.kgraphql.schema.model.InputValueDef
 import com.apurebase.kgraphql.schema.model.PropertyDef
 import com.apurebase.kgraphql.schema.model.TypeDef
 import java.lang.IllegalArgumentException
+import kotlin.reflect.KType
 
 
 class UnionPropertyDSL<T : Any>(val name : String, block: UnionPropertyDSL<T>.() -> Unit) : LimitedAccessItemDSL<T>(), ResolverDSL.Target {
@@ -69,4 +70,8 @@ class UnionPropertyDSL<T : Any>(val name : String, block: UnionPropertyDSL<T>.()
     override fun addInputValues(inputValues: Collection<InputValueDef<*>>) {
         this.inputValues.addAll(inputValues)
     }
+
+    override fun setReturnType(type: KType) {
+        throw IllegalArgumentException("A return value cannot be set on an Union type")
+    }
 }

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/dsl/operations/AbstractOperationDSL.kt

@@ -6,6 +6,7 @@ import com.apurebase.kgraphql.schema.dsl.ResolverDSL
 import com.apurebase.kgraphql.schema.model.FunctionWrapper
 import com.apurebase.kgraphql.schema.model.InputValueDef
 import kotlin.reflect.KFunction
+import kotlin.reflect.KType
 
 
 abstract class AbstractOperationDSL(
@@ -17,10 +18,18 @@ abstract class AbstractOperationDSL(
 
     internal var functionWrapper: FunctionWrapper<*>? = null
 
+    var explicitReturnType: KType? = null
+
     private fun resolver(function: FunctionWrapper<*>): ResolverDSL {
 
-        require(function.hasReturnType()) {
-            "Resolver for '$name' has no return value"
+        try {
+            require(function.hasReturnType()) {
+                "Resolver for '$name' has no return value"
+            }
+        } catch (e: Throwable) {
+            if ("KotlinReflectionInternalError" !in e.toString()) {
+                throw e
+            }
         }
 
         functionWrapper = function
@@ -58,5 +67,8 @@ abstract class AbstractOperationDSL(
         this.inputValues.addAll(inputValues)
     }
 
+    override fun setReturnType(type: KType) {
+        explicitReturnType = type
+    }
 
 }

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/dsl/operations/MutationDSL.kt

@@ -18,7 +18,8 @@ class MutationDSL(
             isDeprecated = isDeprecated,
             deprecationReason = deprecationReason,
             inputValues = inputValues,
-            accessRule = accessRuleBlock
+            accessRule = accessRuleBlock,
+            explicitReturnType = explicitReturnType
         )
     }
 

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/dsl/operations/QueryDSL.kt

@@ -18,7 +18,8 @@ class QueryDSL(
             isDeprecated = isDeprecated,
             deprecationReason = deprecationReason,
             inputValues = inputValues,
-            accessRule = accessRuleBlock
+            accessRule = accessRuleBlock,
+            explicitReturnType = explicitReturnType
         )
     }
 }

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/model/BaseOperationDef.kt

@@ -1,10 +1,16 @@
 package com.apurebase.kgraphql.schema.model
 
 import com.apurebase.kgraphql.Context
+import kotlin.reflect.KType
 
 abstract class BaseOperationDef<T, R>(
         name : String,
         private val operationWrapper: FunctionWrapper<R>,
         val inputValues : List<InputValueDef<*>>,
-        val accessRule : ((T?, Context) -> Exception?)?
-) : Definition(name), OperationDef<R>, FunctionWrapper<R> by operationWrapper
+        val accessRule : ((T?, Context) -> Exception?)?,
+        private val explicitReturnType: KType?
+) : Definition(name), OperationDef<R>, FunctionWrapper<R> by operationWrapper {
+
+        val returnType: KType get() = explicitReturnType ?: kFunction.returnType
+
+}

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/model/MutationDef.kt

@@ -1,6 +1,7 @@
 package com.apurebase.kgraphql.schema.model
 
 import com.apurebase.kgraphql.Context
+import kotlin.reflect.KType
 
 class MutationDef<R> (
         name : String,
@@ -9,5 +10,6 @@ class MutationDef<R> (
         override val isDeprecated: Boolean,
         override val deprecationReason: String?,
         accessRule: ((Nothing?, Context) -> Exception?)? = null,
-        inputValues : List<InputValueDef<*>> = emptyList()
-) : BaseOperationDef<Nothing, R>(name, resolver, inputValues, accessRule), DescribedDef
+        inputValues : List<InputValueDef<*>> = emptyList(),
+        explicitReturnType: KType? = null
+) : BaseOperationDef<Nothing, R>(name, resolver, inputValues, accessRule, explicitReturnType), DescribedDef

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/model/PropertyDef.kt

@@ -18,8 +18,9 @@ interface PropertyDef<T> : Depreciable, DescribedDef {
             override val isDeprecated: Boolean = false,
             override val deprecationReason: String? = null,
             accessRule : ((T?, Context) -> Exception?)? = null,
-            inputValues : List<InputValueDef<*>> = emptyList()
-    ) : BaseOperationDef<T, R>(name, resolver, inputValues, accessRule), PropertyDef<T>
+            inputValues : List<InputValueDef<*>> = emptyList(),
+            explicitReturnType: KType? = null
+    ) : BaseOperationDef<T, R>(name, resolver, inputValues, accessRule, explicitReturnType), PropertyDef<T>
 
     /**
      * [T] -> The Parent Type

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/model/QueryDef.kt

@@ -1,6 +1,7 @@
 package com.apurebase.kgraphql.schema.model
 
 import com.apurebase.kgraphql.Context
+import kotlin.reflect.KType
 
 class QueryDef<R> (
         name : String,
@@ -9,5 +10,6 @@ class QueryDef<R> (
         override val isDeprecated: Boolean = false,
         override val deprecationReason: String? = null,
         accessRule: ((Nothing?, Context) -> Exception?)? = null,
-        inputValues : List<InputValueDef<*>> = emptyList()
-) : BaseOperationDef<Nothing, R>(name, resolver, inputValues, accessRule), DescribedDef
+        inputValues : List<InputValueDef<*>> = emptyList(),
+        explicitReturnType: KType? = null
+) : BaseOperationDef<Nothing, R>(name, resolver, inputValues, accessRule, explicitReturnType), DescribedDef

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/model/SubscriptionDef.kt

@@ -1,6 +1,7 @@
 package com.apurebase.kgraphql.schema.model
 
 import com.apurebase.kgraphql.Context
+import kotlin.reflect.KType
 
 class SubscriptionDef<R> (
         name : String,
@@ -9,5 +10,6 @@ class SubscriptionDef<R> (
         override val isDeprecated: Boolean,
         override val deprecationReason: String?,
         accessRule: ((Nothing?, Context) -> Exception?)? = null,
-        inputValues : List<InputValueDef<*>> = emptyList()
-) : BaseOperationDef<Nothing, R>(name, resolver, inputValues, accessRule), DescribedDef
+        inputValues : List<InputValueDef<*>> = emptyList(),
+        explicitReturnType: KType? = null
+) : BaseOperationDef<Nothing, R>(name, resolver, inputValues, accessRule, explicitReturnType), DescribedDef

kgraphql/src/main/kotlin/com/apurebase/kgraphql/schema/structure/SchemaCompilation.kt

@@ -147,7 +147,7 @@ class SchemaCompilation(
     )
 
     private suspend fun handleOperation(operation : BaseOperationDef<*, *>) : Field {
-        val returnType = handlePossiblyWrappedType(operation.kFunction.returnType, TypeCategory.QUERY)
+        val returnType = handlePossiblyWrappedType(operation.returnType, TypeCategory.QUERY)
         val inputValues = handleInputValues(operation.name, operation, operation.inputValues)
         return Field.Function(operation, returnType, inputValues)
     }
@@ -159,18 +159,26 @@ class SchemaCompilation(
         return Field.Union(unionProperty, unionProperty.nullable, type, inputValues)
     }
 
-    private suspend fun handlePossiblyWrappedType(kType : KType, typeCategory: TypeCategory) : Type = when {
-        kType.isIterable() -> handleCollectionType(kType, typeCategory)
-        kType.jvmErasure == Context::class && typeCategory == TypeCategory.INPUT -> contextType
-        kType.jvmErasure == Execution.Node::class && typeCategory == TypeCategory.INPUT -> executionType
-        kType.jvmErasure == Context::class && typeCategory == TypeCategory.QUERY -> throw SchemaException("Context type cannot be part of schema")
-        kType.arguments.isNotEmpty() -> throw SchemaException("Generic types are not supported by GraphQL, found $kType")
-        kType.jvmErasure.isSealed -> TypeDef.Union(
-            name = kType.jvmErasure.simpleName!!,
-            members = kType.jvmErasure.sealedSubclasses.toSet(),
-            description = null
-        ).let { handleUnionType(it) }
-        else -> handleSimpleType(kType, typeCategory)
+    private suspend fun handlePossiblyWrappedType(kType : KType, typeCategory: TypeCategory) : Type = try {
+        when {
+            kType.isIterable() -> handleCollectionType(kType, typeCategory)
+            kType.jvmErasure == Context::class && typeCategory == TypeCategory.INPUT -> contextType
+            kType.jvmErasure == Execution.Node::class && typeCategory == TypeCategory.INPUT -> executionType
+            kType.jvmErasure == Context::class && typeCategory == TypeCategory.QUERY -> throw SchemaException("Context type cannot be part of schema")
+            kType.arguments.isNotEmpty() -> throw SchemaException("Generic types are not supported by GraphQL, found $kType")
+            kType.jvmErasure.isSealed -> TypeDef.Union(
+                name = kType.jvmErasure.simpleName!!,
+                members = kType.jvmErasure.sealedSubclasses.toSet(),
+                description = null
+            ).let { handleUnionType(it) }
+            else -> handleSimpleType(kType, typeCategory)
+        }
+    } catch (e: Throwable) {
+        if ("KotlinReflectionInternalError" in e.toString()) {
+            throw SchemaException("If you construct a query/mutation generically, you must specify the return type T explicitly with resolver{ ... }.returns<T>()")
+        } else {
+            throw e
+        }
     }
 
     private suspend fun handleCollectionType(kType: KType, typeCategory: TypeCategory): Type {

kgraphql/src/test/kotlin/com/apurebase/kgraphql/schema/SchemaBuilderTest.kt

@@ -1,6 +1,7 @@
 package com.apurebase.kgraphql.schema
 
 import com.apurebase.kgraphql.*
+import com.apurebase.kgraphql.schema.dsl.SchemaBuilder
 import com.apurebase.kgraphql.schema.introspection.TypeKind
 import com.apurebase.kgraphql.schema.scalar.StringScalarCoercion
 import com.apurebase.kgraphql.schema.structure.Field
@@ -603,4 +604,45 @@ class SchemaBuilderTest {
             message shouldBeEqualTo "Resolver for 'main' has no return value"
         }
     }
+
+    inline fun <reified T: Any> SchemaBuilder.createGenericQuery(x: T) {
+        query("data") {
+            resolver { -> x }.returns<T>()
+        }
+    }
+
+    @Test
+    fun `specifying return type explicitly allows generic query creation`(){
+        val schema = defaultSchema {
+            createGenericQuery(InputOne("generic"))
+        }
+
+        assertThat(schema.typeByKClass(InputOne::class), notNullValue())
+    }
+
+    inline fun <reified T: Any> SchemaBuilder.createGenericQueryWithoutReturns(x: T) {
+        query("data") {
+            resolver { -> x }
+        }
+    }
+
+    @Test
+    fun `not specifying return value explicitly with generic query creation throws exception`(){
+        invoking {
+            defaultSchema {
+                createGenericQueryWithoutReturns(InputOne("generic"))
+            }
+        } shouldThrow SchemaException::class with {
+            message shouldBeEqualTo "If you construct a query/mutation generically, you must specify the return type T explicitly with resolver{ ... }.returns<T>()"
+        }
+    }
+
+    @Test
+    fun `specifying return type explicitly allows generic query creation that returns List of T`(){
+        val schema = defaultSchema {
+            createGenericQuery(listOf("generic"))
+        }
+        val result = deserialize(schema.executeBlocking("{data}"))
+        assertThat(result.extract("data/data"), equalTo(listOf("generic")))
+    }
 }