Fixes a JSONUnkeyedDecodingContainer bug (#41)

Author: fabianfett

Sources/PureSwiftJSONCoding/Decoding/JSONUnkeyedDecodingContainer.swift

@@ -112,29 +112,20 @@ struct JSONUnkeyedDecodingContainer: UnkeyedDecodingContainer {
   }
 
   mutating func decode<T>(_ type: T.Type) throws -> T where T : Decodable {
-    defer {
-      currentIndex += 1
-      if currentIndex == count {
-        isAtEnd = true
-      }
-    }
-    
-    let json = array[currentIndex]
-    var newPath = self.codingPath
-    newPath.append(ArrayKey(index: currentIndex))
-    let decoder = JSONDecoderImpl(userInfo: impl.userInfo, from: json, codingPath: newPath)
-  
+    let decoder = try self.decoderForNextElement()
     return try T.init(from: decoder)
   }
 
   mutating func nestedContainer<NestedKey>(keyedBy type: NestedKey.Type) throws
     -> KeyedDecodingContainer<NestedKey> where NestedKey : CodingKey
   {
-    return try impl.container(keyedBy: type)
+    let decoder = try self.decoderForNextElement()
+    return try decoder.container(keyedBy: type)
   }
 
   mutating func nestedUnkeyedContainer() throws -> UnkeyedDecodingContainer {
-    return try impl.unkeyedContainer()
+    let decoder = try self.decoderForNextElement()
+    return try decoder.unkeyedContainer()
   }
 
   mutating func superDecoder() throws -> Decoder {
@@ -144,6 +135,24 @@ struct JSONUnkeyedDecodingContainer: UnkeyedDecodingContainer {
 
 extension JSONUnkeyedDecodingContainer {
 
+  private mutating func decoderForNextElement() throws -> JSONDecoderImpl {
+    defer {
+      currentIndex += 1
+      if currentIndex == count {
+        isAtEnd = true
+      }
+    }
+    
+    let value = array[currentIndex]
+    var newPath = self.codingPath
+    newPath.append(ArrayKey(index: currentIndex))
+    
+    return JSONDecoderImpl(
+      userInfo  : impl.userInfo,
+      from      : value,
+      codingPath: newPath)
+  }
+
   @inline(__always) private func createTypeMismatchError(type: Any.Type, value: JSONValue) -> DecodingError {
     let codingPath = self.codingPath + [ArrayKey(index: currentIndex)]
     return DecodingError.typeMismatch(type, .init(

Tests/JSONCodingTests/Decoding/JSONUnkeyedDecodingContainerTests.swift

@@ -9,99 +9,91 @@ class JSONUnkeyedDecodingContainerTests: XCTestCase {
   func testDecodeNull() {
     let impl = JSONDecoderImpl(userInfo: [:], from: .array([.null]), codingPath: [])
 
-    do {
-      var container = try impl.unkeyedContainer()
-      let result = try container.decodeNil()
-      XCTAssertEqual(result, true)
-      XCTAssertEqual(container.currentIndex, 1)
-    }
-    catch {
-      XCTFail("Unexpected error: \(error)")
-    }
+    var container: UnkeyedDecodingContainer?
+    var result: Bool?
+    XCTAssertNoThrow(container = try impl.unkeyedContainer())
+    XCTAssertNoThrow(result = try container?.decodeNil())
+    XCTAssertEqual(result, true)
+    XCTAssertEqual(container?.currentIndex, 1)
+    XCTAssertEqual(container?.isAtEnd, true)
   }
 
   func testDecodeNullFromArray() {
     let impl = JSONDecoderImpl(userInfo: [:], from: .array([.object([:])]), codingPath: [])
 
-    do {
-      var container = try impl.unkeyedContainer()
-      let result = try container.decodeNil()
-      XCTAssertEqual(result, false)
-      XCTAssertEqual(container.currentIndex, 0)
-    }
-    catch {
-      XCTFail("Unexpected error: \(error)")
-    }
+    var container: UnkeyedDecodingContainer?
+    var result: Bool?
+    XCTAssertNoThrow(container = try impl.unkeyedContainer())
+    XCTAssertNoThrow(result = try container?.decodeNil())
+    XCTAssertEqual(result, false)
+    XCTAssertEqual(container?.currentIndex, 0)
+    XCTAssertEqual(container?.isAtEnd, false)
   }
 
   // MARK: - String -
 
   func testDecodeString() {
     let impl = JSONDecoderImpl(userInfo: [:], from: .array([.string("hello world")]), codingPath: [])
 
-    do {
-      var container = try impl.unkeyedContainer()
-      let result = try container.decode(String.self)
-      XCTAssertEqual(result, "hello world")
-    }
-    catch {
-      XCTFail("Unexpected error: \(error)")
-    }
+    var container: UnkeyedDecodingContainer?
+    var result: String?
+    XCTAssertNoThrow(container = try impl.unkeyedContainer())
+    XCTAssertNoThrow(result = try container?.decode(String.self))
+    XCTAssertEqual(result, "hello world")
+    XCTAssertEqual(container?.currentIndex, 1)
+    XCTAssertEqual(container?.isAtEnd, true)
   }
 
   func testDecodeStringFromNumber() {
     let impl = JSONDecoderImpl(userInfo: [:], from: .array([.number("123")]), codingPath: [])
+    let type = String.self
 
-    do {
-      var container = try impl.unkeyedContainer()
-      let result = try container.decode(String.self)
-      XCTFail("Did not expect to get a result: \(result)")
-    }
-    catch Swift.DecodingError.typeMismatch(let type, let context) {
+    var container: UnkeyedDecodingContainer?
+    XCTAssertNoThrow(container = try impl.unkeyedContainer())
+    XCTAssertThrowsError(_ = try container?.decode(type.self)) { (error) in
+      guard case Swift.DecodingError.typeMismatch(let type, let context) = error else {
+        return XCTFail("Unexpected error: \(error)")
+      }
+      
       // expected
       XCTAssertTrue(type == String.self)
       XCTAssertEqual(context.codingPath.count, 1)
       XCTAssertEqual(context.codingPath.first as? ArrayKey, ArrayKey(index: 0))
       XCTAssertEqual(context.debugDescription, "Expected to decode String but found a number instead.")
     }
-    catch {
-      XCTFail("Unexpected error: \(error)")
-    }
   }
 
   // MARK: - Bool -
 
   func testDecodeBool() {
     let impl = JSONDecoderImpl(userInfo: [:], from: .array([.bool(false)]), codingPath: [])
 
-    do {
-      var container = try impl.unkeyedContainer()
-      let result = try container.decode(Bool.self)
-      XCTAssertEqual(result, false)
-    }
-    catch {
-      XCTFail("Unexpected error: \(error)")
-    }
+    var container: UnkeyedDecodingContainer?
+    var result: Bool?
+    XCTAssertNoThrow(container = try impl.unkeyedContainer())
+    XCTAssertNoThrow(result = try container?.decode(Bool.self))
+    XCTAssertEqual(result, false)
+    XCTAssertEqual(container?.currentIndex, 1)
+    XCTAssertEqual(container?.isAtEnd, true)
   }
 
   func testDecodeBoolFromNumber() {
     let impl = JSONDecoderImpl(userInfo: [:], from: .array([.string("hallo")]), codingPath: [])
-
-    do {
-      var container = try impl.unkeyedContainer()
-      let result = try container.decode(Bool.self)
-      XCTFail("Did not expect to get a result: \(result)")
-    }
-    catch Swift.DecodingError.typeMismatch(let type, let context) {
+    let type = Bool.self
+    
+    var container: UnkeyedDecodingContainer?
+    XCTAssertNoThrow(container = try impl.unkeyedContainer())
+    XCTAssertThrowsError(_ = try container?.decode(type.self)) { (error) in
+      guard case Swift.DecodingError.typeMismatch(let type, let context) = error else {
+        return XCTFail("Unexpected error: \(error)")
+      }
+      
       // expected
       XCTAssertTrue(type == Bool.self)
       XCTAssertEqual(context.codingPath.count, 1)
       XCTAssertEqual(context.codingPath.first as? ArrayKey, ArrayKey(index: 0))
       XCTAssertEqual(context.debugDescription, "Expected to decode Bool but found a string instead.")
     }
-    catch {
-      XCTFail("Unexpected error: \(error)")
-    }
   }
 
   // MARK: - Integer -
@@ -399,24 +391,37 @@ class JSONUnkeyedDecodingContainerTests: XCTestCase {
   func testGetFloatTypeMismatch() {
     let type = Float.self
     let impl = JSONDecoderImpl(userInfo: [:], from: .array([.object([:])]), codingPath: [])
+    
+    var container: UnkeyedDecodingContainer?
+    XCTAssertNoThrow(container = try impl.unkeyedContainer())
+    XCTAssertThrowsError(_ = try container?.decode(type.self)) { (error) in
+      guard case Swift.DecodingError.typeMismatch(let type, let context) = error else {
+        return XCTFail("Unexpected error: \(error)")
+      }
 
-    do {
-      var container = try impl.unkeyedContainer()
-      let result = try container.decode(type.self)
-      XCTFail("Did not expect to get a result: \(result)")
-    }
-    catch Swift.DecodingError.typeMismatch(let type, let context) {
       // expected
       XCTAssertTrue(type == Float.self)
       XCTAssertEqual(context.codingPath.count, 1)
       XCTAssertEqual(context.codingPath.first as? ArrayKey, ArrayKey(index: 0))
       XCTAssertEqual(context.debugDescription, "Expected to decode Float but found a dictionary instead.")
     }
-    catch {
-      XCTFail("Unexpected error: \(error)")
-    }
   }
 
-
+  // MARK: - Containers -
+  
+  func testGetKeyedContainer() {
+    let impl = JSONDecoderImpl(userInfo: [:], from: .array([.object(["foo": .string("bar")])]), codingPath: [])
+    
+    enum CodingKeys: String, CodingKey {
+      case foo
+    }
+    
+    var unkeyedContainer: UnkeyedDecodingContainer?
+    var keyedContainer: KeyedDecodingContainer<CodingKeys>?
+    XCTAssertNoThrow(unkeyedContainer = try impl.unkeyedContainer())
+    XCTAssertNoThrow(keyedContainer = try unkeyedContainer?.nestedContainer(keyedBy: CodingKeys.self))
+    XCTAssertEqual(unkeyedContainer?.isAtEnd, true)
+    XCTAssertEqual("bar", try keyedContainer?.decode(String.self, forKey: .foo))
+  }
 }