fix(api): add collection type casting in swift 5.7 (#3602)

* fix(api): add collection type casting in swift 5.7

* add unit test cases

* add descriptions to test cases

AmplifyPlugins/API/Sources/AWSAPIPlugin/Operation/AWSGraphQLSubscriptionTaskRunner.swift

@@ -378,6 +378,31 @@ fileprivate func toAPIError<R: Decodable>(_ errors: [Error], type: R.Type) -> AP
         (hasAuthorizationError ? ": \(APIError.UnauthorizedMessageString)" : "")
     }
 
+#if swift(<5.8)
+    if let errors = errors.cast(to: AppSyncRealTimeRequest.Error.self) {
+        let hasAuthorizationError = errors.contains(where: { $0 == .unauthorized})
+        return APIError.operationError(
+            errorDescription(hasAuthorizationError),
+            "",
+            errors.first
+        )
+    } else if let errors = errors.cast(to: GraphQLError.self) {
+        let hasAuthorizationError = errors.map(\.extensions)
+            .compactMap { $0.flatMap { $0["errorType"]?.stringValue } }
+            .contains(where: { AppSyncErrorType($0) == .unauthorized })
+        return APIError.operationError(
+            errorDescription(hasAuthorizationError),
+            "",
+            GraphQLResponseError<R>.error(errors)
+        )
+    } else {
+        return APIError.operationError(
+            errorDescription(),
+            "",
+            errors.first
+        )
+    }
+#else
     switch errors {
     case let errors as [AppSyncRealTimeRequest.Error]:
         let hasAuthorizationError = errors.contains(where: { $0 == .unauthorized})
@@ -402,5 +427,5 @@ fileprivate func toAPIError<R: Decodable>(_ errors: [Error], type: R.Type) -> AP
             errors.first
         )
     }
-
+#endif
 }

AmplifyPlugins/API/Sources/AWSAPIPlugin/Support/Utils/Array+Error+TypeCast.swift

@@ -0,0 +1,21 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+
+import Foundation
+
+@_spi(AmplifyAPI)
+extension Array where Element == Error {
+    func cast<T>(to type: T.Type) -> [T]? {
+        self.reduce([]) { partialResult, ele in
+            if let partialResult, let ele = ele as? T {
+                return partialResult + [ele]
+            }
+            return nil
+        }
+    }
+}

AmplifyPlugins/API/Tests/AWSAPIPluginTests/Support/Utils/Array+Error+TypeCastTests.swift

@@ -0,0 +1,62 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+
+import XCTest
+@testable @_spi(AmplifyAPI) import AWSAPIPlugin
+
+class ArrayWithErrorElementExtensionTests: XCTestCase {
+
+    /**
+     Given: errors with generic protocol type
+     When: cast to the correct underlying concrete type
+     Then: successfully casted to underlying concrete type
+     */
+    func testCast_toCorrectErrorType_returnCastedErrorType() {
+        let errors: [Error] = [
+            Error1(), Error1(), Error1()
+        ]
+
+        let error1s = errors.cast(to: Error1.self)
+        XCTAssertNotNil(error1s)
+        XCTAssertTrue(!error1s!.isEmpty)
+        XCTAssertEqual(errors.count, error1s!.count)
+    }
+
+    /**
+     Given: errors with generic protocol type
+     When: cast to the wong underlying concrete type
+     Then: return nil
+     */
+    func testCast_toWrongErrorType_returnNil() {
+        let errors: [Error] = [
+            Error1(), Error1(), Error1()
+        ]
+
+        let error2s = errors.cast(to: Error2.self)
+        XCTAssertNil(error2s)
+    }
+
+    /**
+     Given: errors with generic protocol type
+     When: some of the elements failed to cast to the underlying concrete type
+     Then: return nil
+     */
+
+    func testCast_partiallyToWrongErrorType_returnNil() {
+        let errors: [Error] = [
+            Error2(), Error2(), Error1()
+        ]
+
+        let error2s = errors.cast(to: Error2.self)
+        XCTAssertNil(error2s)
+    }
+
+    struct Error1: Error { }
+
+    struct Error2: Error { }
+}