add extensions field to errors

Sources/GraphQL/Error.swift

@@ -1,10 +1,9 @@
 import Foundation
 
-/// A GraphQLError describes an Error found during the parse, validate, or
-/// execute phases of performing a GraphQL operation. In addition to a message
-/// and stack trace, it also includes information about the locations in a
-/// GraphQL document and/or execution result that correspond to the Error.
-public struct GraphQLError: Codable, Equatable, Sendable {
+/// A GraphQLError describes an Error found during the parse, validate, or execute phases of performing a GraphQL operation. In addition to a message and stack trace, it also includes information about the locations in a GraphQL document and/or execution result that correspond to the Error.
+///
+/// Its implementation follows the specification described at [GraphQLSpec](http://spec.graphql.org/October2021/#sec-Errors.Error-result-format).
+public struct GraphQLError: Codable, Equatable {
 
     /// A short, human-readable summary of the problem.
     public let message: String
@@ -59,16 +58,21 @@ public struct GraphQLError: Codable, Equatable, Sendable {
         }
     }
 
+    /// A map of strings for implementors to add additional information to errors however they see fit, and there are no additional restrictions on its contents.
+    public let extensions: [String: AnyCodable]?
+
     // MARK: - Initializer
 
     public init(
         message: String,
         locations: [Location]? = nil,
-        path: [PathLink]? = nil
+        path: [PathLink]? = nil,
+        extensions: [String: AnyCodable]? = nil
     ) {
         self.message = message
         self.locations = locations
         self.path = path
+        self.extensions = extensions
     }
 }
 

Tests/SwiftGraphQLTests/Selection/SelectionDecodingTests.swift

@@ -285,6 +285,44 @@ final class SelectionDecodingTests: XCTestCase {
             ),
         ])
     }
+
+    func testErrorResponse() throws {
+        let result: ExecutionResult = """
+            {
+              "errors": [
+                {
+                  "message": "Bad Request Exception",
+                  "extensions": {
+                    "code": "BAD_USER_INPUT",
+                  }
+                }
+              ],
+              "data": null
+            }
+            """.execution()
+
+        let selection = Selection<String, String> {
+            switch $0.__state {
+            case let .decoding(data):
+                return try String(from: data)
+            case .selecting:
+                return "wrong"
+            }
+        }
+
+        let decoded = try selection.nullable.decode(raw: result.data)
+        XCTAssertEqual(decoded, nil)
+        XCTAssertEqual(result.errors, [
+            GraphQLError(
+                message: "Bad Request Exception",
+                locations: nil,
+                path: nil,
+                extensions: [
+                    "code": AnyCodable("BAD_USER_INPUT")
+                ]
+            )
+        ])
+    }
 }
 
 extension String {