Support Exit codes from thrown CustomNSError conformers (apple#244)

Introduce customnserror support, so exit code is calculated correctly, resolves apple#243.

Sources/ArgumentParser/Usage/MessageInfo.swift

@@ -62,6 +62,17 @@ enum MessageInfo {
       self.init(error: CommandError(commandStack: [type.asCommand], parserError: e), type: type)
       return
 
+    case let e as CustomNSError:
+      // Send CustomNSError back through the CommandError path
+      self.init(
+        error: CommandError(
+          commandStack: [type.asCommand],
+          parserError: .userValidationError(e)
+        ),
+        type: type
+      )
+      return
+
     default:
       commandStack = [type.asCommand]
       // if the error wasn't one of our two Error types, wrap it as a userValidationError
@@ -92,6 +103,8 @@ enum MessageInfo {
         }
       case let error as ExitCode:
         self = .other(message: "", exitCode: error.rawValue)
+      case let error as CustomNSError:
+        self = .other(message: error.localizedDescription, exitCode: Int32(error.errorCode))
       case let error as LocalizedError where error.errorDescription != nil:
         self = .other(message: error.errorDescription!, exitCode: EXIT_FAILURE)
       default:

Tests/ArgumentParserUnitTests/ExitCodeTests.swift

@@ -76,3 +76,53 @@ extension ExitCodeTests {
     }
   }
 }
+
+// MARK: - CustomNSError tests
+
+extension ExitCodeTests {
+  enum MyCustomNSError: CustomNSError {
+    case myFirstCase
+    case mySecondCase
+
+    var errorCode: Int {
+      switch self {
+      case .myFirstCase:
+        return 101
+      case .mySecondCase:
+        return 102
+      }
+    }
+
+    var errorUserInfo: [String : Any] {
+      switch self {
+      case .myFirstCase:
+        return [NSLocalizedDescriptionKey: "My first case localized description"]
+      case .mySecondCase:
+        return [:]
+      }
+    }
+  }
+
+  struct CheckFirstCustomNSErrorCommand: ParsableCommand {
+
+    @Option
+    var errorCase: Int
+
+    func run() throws {
+      switch errorCase {
+      case 101:
+        throw MyCustomNSError.myFirstCase
+      default:
+        throw MyCustomNSError.mySecondCase
+      }
+    }
+  }
+
+  func testCustomErrorCodeForTheFirstCase() {
+    XCTAssertEqual(CheckFirstCustomNSErrorCommand.exitCode(for: MyCustomNSError.myFirstCase), ExitCode(rawValue: 101))
+  }
+
+  func testCustomErrorCodeForTheSecondCase() {
+    XCTAssertEqual(CheckFirstCustomNSErrorCommand.exitCode(for: MyCustomNSError.mySecondCase), ExitCode(rawValue: 102))
+  }
+}