fix: Expose ExplainEnum in the GQL schema (#1204)

Adds ExplainEnum to the GQL schema. It fixes the introspection query error with Altair and GraphiQL.
Adds a test for the enum existence in resulting response schema.

Author: orpheuslummis

request/graphql/schema/manager.go

@@ -160,5 +160,7 @@ func defaultTypes() []gql.Type {
 		schemaTypes.CommitLinkObject,
 		schemaTypes.CommitObject,
 		schemaTypes.DeltaObject,
+
+		schemaTypes.ExplainEnum,
 	}
 }

request/graphql/schema/types/types.go

@@ -38,7 +38,8 @@ var (
 	})
 
 	ExplainEnum = gql.NewEnum(gql.EnumConfig{
-		Name: "ExplainType",
+		Name:        "ExplainType",
+		Description: "ExplainType is an enum selecting the type of explanation done by the @explain directive.",
 		Values: gql.EnumValueConfigMap{
 			ExplainArgSimple: &gql.EnumValueConfig{
 				Value:       ExplainArgSimple,
@@ -48,7 +49,8 @@ var (
 	})
 
 	ExplainDirective *gql.Directive = gql.NewDirective(gql.DirectiveConfig{
-		Name: ExplainLabel,
+		Name:        ExplainLabel,
+		Description: "@explain is a directive that can be used to explain the query.",
 		Args: gql.FieldConfigArgument{
 			ExplainArgNameType: &gql.ArgumentConfig{
 				Type: ExplainEnum,

tests/integration/schema/client_test.go

@@ -0,0 +1,49 @@
+// Copyright 2022 Democratized Data Foundation
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+package schema
+
+import (
+	"testing"
+
+	schemaTypes "github.com/sourcenetwork/defradb/request/graphql/schema/types"
+)
+
+// TestIntrospectionExplainTypeDefined tests that the introspection query returns a schema that
+// defines the ExplainType enum.
+func TestIntrospectionExplainTypeDefined(t *testing.T) {
+	test := RequestTestCase{
+		Schema: []string{},
+		IntrospectionRequest: `
+			query IntrospectionQuery {
+				__schema {
+					types {
+						kind
+						name
+						description
+					}
+				}
+			}
+		`,
+		ContainsData: map[string]any{
+			"__schema": map[string]any{
+				"types": []any{
+					map[string]any{
+						"description": schemaTypes.ExplainEnum.Description(),
+						"kind":        "ENUM",
+						"name":        "ExplainType",
+					},
+				},
+			},
+		},
+	}
+
+	ExecuteRequestTestCase(t, test)
+}