Allow abuse errors to be overridden to prevent preconditionFailure

Sources/Pwomise/PendingPromise.swift

@@ -7,8 +7,8 @@
 
 import Foundation
 
-internal enum PendingPromise<Output, Failure: Error>: Equatable, CustomDebugStringConvertible {
- internal static func == (lhs: PendingPromise<Output, Failure>, rhs: PendingPromise<Output, Failure>) -> Bool {
+public enum PendingPromise<Output, Failure: Error>: Equatable, CustomDebugStringConvertible {
+ public static func == (lhs: PendingPromise<Output, Failure>, rhs: PendingPromise<Output, Failure>) -> Bool {
  switch lhs {
  case .pending:
  switch rhs {
@@ -30,7 +30,7 @@ internal enum PendingPromise<Output, Failure: Error>: Equatable, CustomDebugStri
  case pending
  case resolved(Result<Output, Failure>)
 
- internal var debugDescription: String {
+ public var debugDescription: String {
  switch self {
  case .pending:
  return "pending"

Sources/Pwomise/Pwomise.swift

@@ -12,6 +12,12 @@ public enum PromiseInconsistencyError: Error {
  case opaqueMismatch
 }
 
+public protocol PromiseAbuseDelegate {
+ func promise<T>(_ promise: Promise<T>, doubleResolvedWithResult result: PendingPromise<T, Error>, resolutionStackTrace: [String], abusingStackTrace: [String])
+}
+
+public var SharedPromiseAbuseDelegate: PromiseAbuseDelegate?
+
 public class Promise<Output>: CustomDebugStringConvertible {
  internal typealias Pending = PendingPromise<Output, Error>
  public typealias Completion = Result<Output, Error>
@@ -89,9 +95,16 @@ public class Promise<Output>: CustomDebugStringConvertible {
  willSet {
  guard result == .pending, newValue != .pending else {
  /// Result can only be set once – its a promise of a result, not a publisher
- print(resolutionStackTrace.joined(separator: "\n"))
- preconditionFailure("result is omnidirectional, from pending to resolved.")
+ if let abuseDelegate = SharedPromiseAbuseDelegate {
+ abuseDelegate.promise(self, doubleResolvedWithResult: newValue, resolutionStackTrace: resolutionStackTrace, abusingStackTrace: Thread.callStackSymbols)
+ } else {
+ print(resolutionStackTrace.joined(separator: "\n"))
+ preconditionFailure("result is omnidirectional, from pending to resolved.")
+ }
+
+ return
  }
+
  resolutionStackTrace = Thread.callStackSymbols
  }
  }
@@ -109,26 +122,14 @@ public class Promise<Output>: CustomDebugStringConvertible {
 
  public init(_ cb: (@escaping Resolve, @escaping Reject) -> ()) {
  cb({ output in
- guard self.pending else {
- preconditionFailure("cannot overwrite promise state")
- }
-
  self.result = .resolved(.success(output))
  }, { error in
- guard self.pending else {
- preconditionFailure("cannot overwrite promise state")
- }
-
  self.result = .resolved(.failure(error))
  })
  }
 
  public init(_ cb: (@escaping Resolve) -> ()) {
  cb({ output in
- guard self.pending else {
- preconditionFailure("cannot overwrite promise state")
- }
-
  self.result = .resolved(.success(output))
  })
  }