better integration with NSError (#195)

motivation: some of TSC errors go through Foundation layers and can loose information (the description specifically) when crossing the Error <> NSError boundries

changes: conform most Error types to CustomNSError and provide the description via NSLocalizedDescriptionKey

rdar://74712707

Author: tomerd

Sources/TSCBasic/FileSystem.swift

@@ -12,7 +12,7 @@ import TSCLibc
 import Foundation
 import Dispatch
 
-public struct FileSystemError: Swift.Error, Equatable {
+public struct FileSystemError: Error, Equatable {
     public enum Kind: Equatable {
         /// Access to the path is denied.
         ///
@@ -80,6 +80,12 @@ public struct FileSystemError: Swift.Error, Equatable {
     }
 }
 
+extension FileSystemError: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: "\(self)"]
+    }
+}
+
 public extension FileSystemError {
     init(errno: Int32, _ path: AbsolutePath) {
         switch errno {

Sources/TSCBasic/GraphAlgorithms.swift

@@ -8,7 +8,7 @@
  See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
-public enum GraphError: Swift.Error {
+public enum GraphError: Error {
     /// A cycle was detected in the input.
     case unexpectedCycle
 }

Sources/TSCBasic/JSON.swift

@@ -169,11 +169,17 @@ extension JSON: ByteStreamable {
 
 import Foundation
 
-enum JSONDecodingError: Swift.Error {
+enum JSONDecodingError: Error {
     /// The input byte string is malformed.
     case malformed
 }
 
+extension JSONDecodingError: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: "\(self)"]
+    }
+}
+
 // NOTE: This implementation is carefully crafted to work correctly on both
 // Linux and OS X while still compiling for both. Thus, the implementation takes
 // Any even though it could take AnyObject on OS X, and it uses converts to

Sources/TSCBasic/Lock.swift

@@ -35,10 +35,15 @@ public struct Lock {
     }
 }
 
-enum ProcessLockError: Swift.Error {
+enum ProcessLockError: Error {
     case unableToAquireLock(errno: Int32)
 }
 
+extension ProcessLockError: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: "\(self)"]
+    }
+}
 /// Provides functionality to aquire a lock on a file via POSIX's flock() method.
 /// It can be used for things like serializing concurrent mutations on a shared resource
 /// by mutiple instances of a process. The `FileLock` is not thread-safe.

Sources/TSCBasic/Path.swift

@@ -18,6 +18,9 @@ private typealias PathImpl = UNIXPath
 private typealias PathImpl = UNIXPath
 #endif
 
+import protocol Foundation.CustomNSError
+import var Foundation.NSLocalizedDescriptionKey
+
 /// Represents an absolute file system path, independently of what (or whether
 /// anything at all) exists at that path in the file system at any given time.
 /// An absolute path always starts with a `/` character, and holds a normalized
@@ -913,6 +916,12 @@ extension AbsolutePath {
 
 }
 
+extension PathValidationError: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: self.description]
+    }
+}
+
 // FIXME: We should consider whether to merge the two `normalize()` functions.
 // The argument for doing so is that some of the code is repeated; the argument
 // against doing so is that some of the details are different, and since any

Sources/TSCBasic/Process.swift

@@ -9,6 +9,8 @@
 */
 
 import class Foundation.ProcessInfo
+import protocol Foundation.CustomNSError
+import var Foundation.NSLocalizedDescriptionKey
 
 #if os(Windows)
 import Foundation
@@ -755,6 +757,13 @@ extension Process.Error: CustomStringConvertible {
         }
     }
 }
+
+extension Process.Error: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: self.description]
+    }
+}
+
 #endif
 
 extension ProcessResult.Error: CustomStringConvertible {
@@ -795,3 +804,9 @@ extension ProcessResult.Error: CustomStringConvertible {
         }
     }
 }
+
+extension ProcessResult.Error: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: self.description]
+    }
+}

Sources/TSCBasic/Result.swift

@@ -8,6 +8,9 @@
  See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 */
 
+import protocol Foundation.CustomNSError
+import var Foundation.NSLocalizedDescriptionKey
+
 extension Result where Failure == Error {
     public func tryMap<NewSuccess>(_ closure: (Success) throws -> NewSuccess) -> Result<NewSuccess, Error> {
         flatMap({ value in
@@ -30,6 +33,12 @@ public struct StringError: Equatable, Codable, CustomStringConvertible, Error {
     }
 }
 
+extension StringError: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: self.description]
+    }
+}
+
 extension Result where Failure == StringError {
     /// Create an instance of Result<Value, StringError>.
     ///

Sources/TSCBasic/TemporaryFile.swift

@@ -12,8 +12,10 @@ import TSCLibc
 import class Foundation.FileHandle
 import class Foundation.FileManager
 import func Foundation.NSTemporaryDirectory
+import protocol Foundation.CustomNSError
+import var Foundation.NSLocalizedDescriptionKey
 
-public enum TempFileError: Swift.Error {
+public enum TempFileError: Error {
     /// Could not create a unique temporary filename.
     case couldNotCreateUniqueName
 
@@ -26,6 +28,12 @@ public enum TempFileError: Swift.Error {
     case couldNotFindTmpDir
 }
 
+extension TempFileError: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: "\(self)"]
+    }
+}
+
 private extension TempFileError {
     init(errno: Int32) {
         switch errno {
@@ -150,7 +158,7 @@ public func withTemporaryFile<Result>(
 // FIXME: This isn't right place to declare this, probably POSIX or merge with FileSystemError?
 //
 /// Contains the error which can be thrown while creating a directory using POSIX's mkdir.
-public enum MakeDirectoryError: Swift.Error {
+public enum MakeDirectoryError: Error {
     /// The given path already exists as a directory, file or symbolic link.
     case pathExists
     /// The path provided was too long.
@@ -189,6 +197,12 @@ private extension MakeDirectoryError {
     }
 }
 
+extension MakeDirectoryError: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: "\(self)"]
+    }
+}
+
 /// Creates a temporary directory and evaluates a closure with the directory path as an argument.
 /// The temporary directory will live on disk while the closure is evaluated and will be deleted afterwards.
 ///

Sources/TSCBasic/misc.swift

@@ -157,7 +157,7 @@ extension AbsolutePath {
 }
 
 // FIXME: Eliminate or find a proper place for this.
-public enum SystemError: Swift.Error {
+public enum SystemError: Error {
     case chdir(Int32, String)
     case close(Int32)
     case exec(Int32, path: String, args: [String])
@@ -236,6 +236,12 @@ extension SystemError: CustomStringConvertible {
     }
 }
 
+extension SystemError: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: self.description]
+    }
+}
+
 /// Memoizes a costly computation to a cache variable.
 public func memoize<T>(to cache: inout T?, build: () throws -> T) rethrows -> T {
     if let value = cache {

Sources/TSCUtility/JSONMessageStreamingParser.swift

@@ -82,7 +82,14 @@ public final class JSONMessageStreamingParser<Delegate: JSONMessageStreamingPars
 private extension JSONMessageStreamingParser {
 
     /// Error corresponding to invalid Swift compiler output.
-    struct ParsingError: LocalizedError {
+    struct ParsingError: CustomStringConvertible, LocalizedError {
+        var description: String {
+            if let error = underlyingError {
+                return "\(reason): \(error)"
+            } else {
+                return reason
+            }
+        }
 
         /// Text describing the specific reason for the parsing failure.
         let reason: String
@@ -91,11 +98,7 @@ private extension JSONMessageStreamingParser {
         let underlyingError: Error?
 
         var errorDescription: String? {
-            if let error = underlyingError {
-                return "\(reason): \(error)"
-            } else {
-                return reason
-            }
+            self.description
         }
     }
 
@@ -171,3 +174,9 @@ private extension JSONMessageStreamingParser {
 }
 
 private let newline = UInt8(ascii: "\n")
+
+extension JSONMessageStreamingParser.ParsingError: CustomNSError {
+    public var errorUserInfo: [String : Any] {
+        return [NSLocalizedDescriptionKey: self.description]
+    }
+}