improve error reporting

Author: ktoso

stdlib/public/Distributed/DistributedActorSystem.swift

@@ -212,6 +212,10 @@ extension DistributedActorSystem {
   ///           some other mismatch between them happens. In general, this
   ///           method is allowed to throw in any situation that might otherwise
   ///           result in an illegal or unexpected invocation being performed.
+  ///
+  ///           Throws ``ExecuteDistributedTargetMissingAccessorError`` if the `target`
+  ///           does not resolve to a valid distributed function accessor, i.e. the
+  ///           call identifier is incorrect, corrupted, or simply not present in this process.
   public func executeDistributedTarget<Act>(
     on actor: Act,
     target: RemoteCallTarget,
@@ -574,10 +578,28 @@ public protocol DistributedActorSystemError: Error {}
 
 @available(SwiftStdlib 5.7, *)
 public struct ExecuteDistributedTargetError: DistributedActorSystemError {
-  let message: String
+  public let errorCode: ErrorCode
+  public let message: String
+
+  public enum ErrorCode {
+    /// Thrown when unable to resolve the target identifier to a function accessor.
+    /// This can happen when the identifier is corrupt, illegal, or wrong in the
+    /// sense that the caller and callee do not have the called function recorded
+    /// using the same identifier.
+    case targetAccessorNotFound
+
+    /// A general issue during the execution of the distributed call target ocurred.
+    case other
+  }
 
   public init(message: String) {
     self.message = message
+    self.errorCode = .other
+  }
+
+  public init(message: String, errorCode: ErrorCode) {
+    self.message = message
+    self.errorCode = errorCode
   }
 }
 

stdlib/public/Distributed/DistributedMetadata.swift

@@ -112,10 +112,9 @@ func _getWitnessTablesFor(
 @available(SwiftStdlib 5.7, *)
 @_silgen_name("swift_distributed_makeDistributedTargetAccessorNotFoundError")
 internal // SPI Distributed
-func _makeDistributedTargetAccessorNotFoundError(
-  _ targetNameStart: UnsafePointer<UInt8>,
-  _ targetNameLength: UInt
-) -> Error {
-  let name = String(decodingCString: targetNameStart, as: Unicode.UTF8.self)
-  return ExecuteDistributedTargetError(message: "Could not find distributed accessor for target \(name)")
+func _makeDistributedTargetAccessorNotFoundError() -> Error {
+  /// We don't include the name of the target in case the input was compromised.
+  return ExecuteDistributedTargetError(
+    message: "Failed to locate distributed function accessor",
+    errorCode: .targetAccessorNotFound)
 }

test/Distributed/Runtime/distributed_actor_func_calls_remoteCall_bad_targets.swift

@@ -57,10 +57,12 @@ func test() async throws {
       returning: String.self
     )
   } catch {
-    // CHECK: << onThrow: ExecuteDistributedTargetError(message: "Could not find distributed accessor for target $s9BADMODULE7GreeterC5greet4nameS2S_tYaKFTE")
-    // CHECK: << remoteCall throw: ExecuteDistributedTargetError(message: "Could not find distributed accessor for target $s9BADMODULE7GreeterC5greet4nameS2S_tYaKFTE")
+    // CHECK: << onThrow: ExecuteDistributedTargetError(errorCode: Distributed.ExecuteDistributedTargetError.ErrorCode.targetAccessorNotFound, message: "Failed to locate distributed function accessor")
+    // CHECK: << remoteCall throw: ExecuteDistributedTargetError(errorCode: Distributed.ExecuteDistributedTargetError.ErrorCode.targetAccessorNotFound, message: "Failed to locate distributed function accessor")
     print("caught error: \(error)")
-    // CHECK: caught error: ExecuteDistributedTargetError(message: "Could not find distributed accessor for target $s9BADMODULE7GreeterC5greet4nameS2S_tYaKFTE")
+    print("call target was: \(badTarget.identifier)")
+    // CHECK: caught error: ExecuteDistributedTargetError(errorCode: Distributed.ExecuteDistributedTargetError.ErrorCode.targetAccessorNotFound, message: "Failed to locate distributed function accessor")
+    // CHECK: call target was: $s9BADMODULE7GreeterC5greet4nameS2S_tYaKFTE
   }
 }
 

test/Distributed/Runtime/distributed_actor_remoteCall.swift

@@ -492,7 +492,7 @@ func test() async throws {
     invocationDecoder: &decodeErrDecoder,
     handler: FakeResultHandler()
   )
-  // CHECK: ERROR: ExecuteDistributedTargetError(message: "Failed to decode of Int??? (for a test)")
+  // CHECK: ERROR: ExecuteDistributedTargetError(errorCode: Distributed.ExecuteDistributedTargetError.ErrorCode.other, message: "Failed to decode of Int??? (for a test)")
 
   print("done")
   // CHECK-NEXT: done