fix: Expose ExplainEnum in the GQL schema

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

@@ -37,6 +37,7 @@ var (
 		},
 	})
 
+	// ExplainEnum is an enum for the @explain directive.
 	ExplainEnum = gql.NewEnum(gql.EnumConfig{
 		Name: "ExplainType",
 		Values: gql.EnumValueConfigMap{
@@ -47,6 +48,7 @@ var (
 		},
 	})
 
+	// ExplainDirective @explain is used to explain the query.
 	ExplainDirective *gql.Directive = gql.NewDirective(gql.DirectiveConfig{
 		Name: ExplainLabel,
 		Args: gql.FieldConfigArgument{

tests/integration/schema/client_test.go

@@ -0,0 +1,143 @@
+// 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"
+)
+
+const clientIntrospectionRequest string = `
+query IntrospectionQuery {
+	__schema {
+	queryType { name }
+	mutationType { name }
+	subscriptionType { name }
+	types {
+		...FullType
+	}
+	directives {
+		name
+		description
+		locations
+		args {
+		...InputValue
+		}
+	}
+	}
+}
+
+fragment FullType on __Type {
+	kind
+	name
+	description
+	fields(includeDeprecated: true) {
+	name
+	description
+	args {
+		...InputValue
+	}
+	type {
+		...TypeRef
+	}
+	isDeprecated
+	deprecationReason
+	}
+	inputFields {
+	...InputValue
+	}
+	interfaces {
+	...TypeRef
+	}
+	enumValues(includeDeprecated: true) {
+	name
+	description
+	isDeprecated
+	deprecationReason
+	}
+	possibleTypes {
+	...TypeRef
+	}
+}
+
+fragment InputValue on __InputValue {
+	name
+	description
+	type { ...TypeRef }
+	defaultValue
+}
+
+fragment TypeRef on __Type {
+	kind
+	name
+	ofType {
+	kind
+	name
+	ofType {
+		kind
+		name
+		ofType {
+		kind
+		name
+		ofType {
+			kind
+			name
+			ofType {
+			kind
+			name
+			ofType {
+				kind
+				name
+				ofType {
+				kind
+				name
+				}
+			}
+			}
+		}
+		}
+	}
+	}
+}
+  `
+
+// TestClientIntrospectionExplainTypeDefined tests that the introspection query returns a schema that
+// defines the ExplainType enum.
+func TestClientIntrospectionExplainTypeDefined(t *testing.T) {
+	test := RequestTestCase{
+		Schema:               []string{},
+		IntrospectionRequest: clientIntrospectionRequest,
+		ContainsData: map[string]any{
+			"__schema": map[string]any{
+				"types": []any{
+					map[string]any{
+						"description": "",
+						"enumValues": []any{
+							map[string]any{
+								"deprecationReason": nil,
+								"description":       "Simple explaination - dump of the plan graph.",
+								"isDeprecated":      false,
+								"name":              "simple",
+							},
+						},
+						"fields":        nil,
+						"inputFields":   nil,
+						"interfaces":    nil,
+						"kind":          "ENUM",
+						"name":          "ExplainType",
+						"possibleTypes": nil,
+					},
+				},
+			},
+		},
+	}
+
+	ExecuteRequestTestCase(t, test)
+}