Improve Error to NSError conversion

Darwin Foundation converts to NSError any type, which conforms Error protocol and doesn't conform CustomNSError, the same way as if it conforms CustomNSError with default implementation. Foundation should behave the same way on other platforms.

Author: Konstiantyn Gominyuk

Sources/Foundation/NSError.swift

@@ -1410,8 +1410,8 @@ func _convertErrorToNSError(_ error: Error) -> NSError {
             code = error.errorCode
             userInfo = error.errorUserInfo
         } else {
-            domain = "SwiftError"
-            code = 0
+            domain = error._domain
+            code = error._code
             userInfo = (_swift_Foundation_getErrorDefaultUserInfo(error) as? [String : Any]) ?? [:]
         }
 

Tests/Foundation/Tests/TestNSError.swift

@@ -22,7 +22,12 @@ class TestNSError : XCTestCase {
             ("test_CustomNSError_errorCode", test_CustomNSError_errorCode),
             ("test_CustomNSError_errorCodeRawInt", test_CustomNSError_errorCodeRawInt),
             ("test_CustomNSError_errorCodeRawUInt", test_CustomNSError_errorCodeRawUInt),
-            ("test_errorConvenience", test_errorConvenience)
+            ("test_errorConvenience", test_errorConvenience),
+            ("test_ConvertErrorToNSError_domain", test_ConvertErrorToNSError_domain),
+            ("test_ConvertErrorToNSError_errorCode", test_ConvertErrorToNSError_errorCode),
+            ("test_ConvertErrorToNSError_errorCodeRawInt", test_ConvertErrorToNSError_errorCodeRawInt),
+            ("test_ConvertErrorToNSError_errorCodeRawUInt", test_ConvertErrorToNSError_errorCodeRawUInt),
+            ("test_ConvertErrorToNSError_errorCodeWithAssosiatedValue", test_ConvertErrorToNSError_errorCodeWithAssosiatedValue),
         ]
     }
 
@@ -106,6 +111,59 @@ class TestNSError : XCTestCase {
             XCTFail()
         }
     }
+    
+    func test_ConvertErrorToNSError_domain() {
+        struct CustomSwiftError: Error {
+        }
+        XCTAssertTrue((CustomSwiftError() as NSError).domain.contains("CustomSwiftError"))
+    }
+    
+    func test_ConvertErrorToNSError_errorCode() {
+        enum SwiftError: Error {
+            case zero
+            case one
+            case two
+        }
+        
+        XCTAssertEqual((SwiftError.zero as NSError).code, 0)
+        XCTAssertEqual((SwiftError.one as NSError).code, 1)
+        XCTAssertEqual((SwiftError.two as NSError).code, 2)
+    }
+    
+    func test_ConvertErrorToNSError_errorCodeRawInt() {
+        enum SwiftError: Int, Error {
+            case minusOne = -1
+            case fortyTwo = 42
+        }
+        
+        XCTAssertEqual((SwiftError.minusOne as NSError).code, -1)
+        XCTAssertEqual((SwiftError.fortyTwo as NSError).code, 42)
+    }
+    
+    func test_ConvertErrorToNSError_errorCodeRawUInt() {
+        enum SwiftError: UInt, Error {
+            case fortyTwo = 42
+        }
+        
+        XCTAssertEqual((SwiftError.fortyTwo as NSError).code, 42)
+    }
+    
+    func test_ConvertErrorToNSError_errorCodeWithAssosiatedValue() {
+        enum SwiftError: Error {
+            case one
+            case two
+            case three(String)
+            case four
+            case five(String)
+        }
+        
+        XCTAssertEqual((SwiftError.one as NSError).code, 2)
+        XCTAssertEqual((SwiftError.two as NSError).code, 3)
+        XCTAssertEqual((SwiftError.three("three") as NSError).code, 0)
+        XCTAssertEqual((SwiftError.four as NSError).code, 4)
+        XCTAssertEqual((SwiftError.five("five") as NSError).code, 1)
+    }
+
 }
 
 class TestURLError: XCTestCase {