[yams-1.0-branch] _KeyedDecodingContainer and _UnkeyedDecodingContainer did not properly decode null

CHANGELOG.md

@@ -19,6 +19,10 @@
   [Norio Nomura](https://github.com/norio-nomura)
   [#146](https://github.com/jpsim/Yams/pull/146)
 
+* Fix null/~/NULL/Null were parsed as strings, not nil by `YAMLDecoder`.  
+  [Norio Nomura](https://github.com/norio-nomura)
+  [#157](https://github.com/jpsim/Yams/issues/157)
+
 ## 1.0.1
 
 ##### Breaking

Sources/Yams/Decoder.swift

@@ -109,7 +109,7 @@ private struct _KeyedDecodingContainer<Key: CodingKey> : KeyedDecodingContainerP
     func contains(_ key: Key) -> Bool { return mapping[key.stringValue] != nil }
 
     func decodeNil(forKey key: Key) throws -> Bool {
-        return try node(for: key) == Node("null", Tag(.null))
+        return try decoder(for: key).decodeNil()
     }
 
     func decode<T>(_ type: T.Type, forKey key: Key) throws -> T where T: Decodable & ScalarConstructible {
@@ -166,12 +166,7 @@ private struct _UnkeyedDecodingContainer: UnkeyedDecodingContainer {
 
     mutating func decodeNil() throws -> Bool {
         try throwErrorIfAtEnd(Any?.self)
-        if currentNode == Node("null", Tag(.null)) {
-            currentIndex += 1
-            return true
-        } else {
-            return false
-        }
+        return try currentDecoder { $0.decodeNil() }
     }
 
     mutating func decode<T>(_ type: T.Type) throws -> T where T: Decodable & ScalarConstructible {

Tests/YamsTests/EncoderTests.swift

@@ -316,6 +316,29 @@ class EncoderTests: XCTestCase { // swiftlint:disable:this type_body_length
         expectEqual(type(of: decoded), Employee.self, "Expected decoded value to be of type Employee; got \(type(of: decoded)) instead.")
     }
 
+    func test_null_yml() throws {
+        let s = """
+              n1: ~
+              n2: null
+              n3: NULL
+              n4: Null
+              n5:
+            """
+        struct Test: Decodable {
+            let n1: String?
+            let n2: String?
+            let n3: String?
+            let n4: String?
+            let n5: String?
+        }
+        let t = try YAMLDecoder().decode(Test.self, from: s)
+        XCTAssertNil(t.n1)
+        XCTAssertNil(t.n2)
+        XCTAssertNil(t.n3)
+        XCTAssertNil(t.n4)
+        XCTAssertNil(t.n5)
+    }
+
     // MARK: - Helper Functions
 
     private func _testRoundTrip<T>(of value: T,
@@ -1089,7 +1112,8 @@ extension EncoderTests {
             ("testValuesInUnkeyedContainer", testValuesInUnkeyedContainer),
             ("testDictionary", testDictionary),
             ("testNodeTypeMismatch", testNodeTypeMismatch),
-            ("testDecodingConcreteTypeParameter", testDecodingConcreteTypeParameter)
+            ("testDecodingConcreteTypeParameter", testDecodingConcreteTypeParameter),
+            ("test_null_yml", test_null_yml)
         ]
     }
 }