Add back the missing code that handle source=="vals[i]" code.

src/System.Private.Xml/src/System/Xml/Serialization/XmlSerializationReaderILGen.cs

@@ -799,30 +799,52 @@ private void WritePrimitive(TypeMapping mapping, string source)
             }
             else if (mapping.TypeDesc.FormatterName == "String")
             {
-                System.Diagnostics.Debug.Assert(source == "Reader.Value" || source == "Reader.ReadElementString()");
-                MethodInfo XmlSerializationReader_get_Reader = typeof(XmlSerializationReader).GetMethod(
-                     "get_Reader",
-                     CodeGenerator.InstanceBindingFlags,
-                     Array.Empty<Type>()
-                     );
-                MethodInfo XmlReader_method = typeof(XmlReader).GetMethod(
-                    source == "Reader.Value" ? "get_Value" : "ReadElementContentAsString",
-                    CodeGenerator.InstanceBindingFlags,
-                    Array.Empty<Type>()
-                    );
-                if (mapping.TypeDesc.CollapseWhitespace)
-                    ilg.Ldarg(0);
-                ilg.Ldarg(0);
-                ilg.Call(XmlSerializationReader_get_Reader);
-                ilg.Call(XmlReader_method);
-                if (mapping.TypeDesc.CollapseWhitespace)
+                System.Diagnostics.Debug.Assert(source == "Reader.Value" || source == "Reader.ReadElementString()" || source == "vals[i]");
+                if (source == "vals[i]")
+                {
+                    if (mapping.TypeDesc.CollapseWhitespace)
+                        ilg.Ldarg(0);
+                    LocalBuilder locVals = ilg.GetLocal("vals");
+                    LocalBuilder locI = ilg.GetLocal("i");
+                    ilg.LoadArrayElement(locVals, locI);
+                    if (mapping.TypeDesc.CollapseWhitespace)
+                    {
+                        MethodInfo XmlSerializationReader_CollapseWhitespace = typeof(XmlSerializationReader).GetMethod(
+                            "CollapseWhitespace",
+                            CodeGenerator.InstanceBindingFlags,
+                            null,
+                            new Type[] { typeof(String) },
+                            null
+                            );
+                        ilg.Call(XmlSerializationReader_CollapseWhitespace);
+                    }
+                }
+                else
                 {
-                    MethodInfo XmlSerializationReader_CollapseWhitespace = typeof(XmlSerializationReader).GetMethod(
-                        "CollapseWhitespace",
+                    MethodInfo XmlSerializationReader_get_Reader = typeof(XmlSerializationReader).GetMethod(
+                         "get_Reader",
+                         CodeGenerator.InstanceBindingFlags,
+                         Array.Empty<Type>()
+                         );
+                    MethodInfo XmlReader_method = typeof(XmlReader).GetMethod(
+                        source == "Reader.Value" ? "get_Value" : "ReadElementContentAsString",
                         CodeGenerator.InstanceBindingFlags,
-                        new Type[] { typeof(string) }
+                        Array.Empty<Type>()
                         );
-                    ilg.Call(XmlSerializationReader_CollapseWhitespace);
+                    if (mapping.TypeDesc.CollapseWhitespace)
+                        ilg.Ldarg(0);
+                    ilg.Ldarg(0);
+                    ilg.Call(XmlSerializationReader_get_Reader);
+                    ilg.Call(XmlReader_method);
+                    if (mapping.TypeDesc.CollapseWhitespace)
+                    {
+                        MethodInfo XmlSerializationReader_CollapseWhitespace = typeof(XmlSerializationReader).GetMethod(
+                            "CollapseWhitespace",
+                            CodeGenerator.InstanceBindingFlags,
+                            new Type[] { typeof(string) }
+                            );
+                        ilg.Call(XmlSerializationReader_CollapseWhitespace);
+                    }
                 }
             }
             else

src/System.Private.Xml/tests/XmlSerializer/XmlSerializerTests.cs

@@ -1691,6 +1691,22 @@ public static void SerializeWithDefaultValueSetToNegativeInfinityTest()
         Assert.True(result);
     }
 
+    [Fact]
+    public static void DeserializeIDREFSIntoStringTest()
+    {
+        string xmlstring = @"<?xml version = ""1.0"" encoding = ""utf-8"" ?><Document xmlns = ""http://example.com"" id = ""ID1"" refs=""ID1 ID2 ID3"" ></Document>";
+        Stream ms = GenerateStreamFromString(xmlstring);
+        XmlSerializer ser = new XmlSerializer(typeof(MsgDocumentType));
+        var value = (MsgDocumentType)ser.Deserialize(ms);
+        Assert.NotNull(value);
+        Assert.Equal("ID1", value.Id);
+        Assert.NotNull(value.Refs);
+        Assert.Equal(3, value.Refs.Count());
+        Assert.Equal("ID1", value.Refs[0]);
+        Assert.Equal("ID2", value.Refs[1]);
+        Assert.Equal("ID3", value.Refs[2]);
+    }
+
     private static bool SerializeWithDefaultValue<T>(T value, string baseline)
     {
         XmlSerializer serializer = new XmlSerializer(typeof(T));

src/System.Runtime.Serialization.Xml/tests/SerializationTypes.cs

@@ -1243,3 +1243,15 @@ public int IntValue
         }
     }
 }
+
+[Serializable()]
+[System.Xml.Serialization.XmlType("MsgDocumentType", Namespace = "http://example.com")]
+[System.Xml.Serialization.XmlRoot("Document", Namespace = "http://example.com")]
+public partial class MsgDocumentType
+{
+    [System.Xml.Serialization.XmlAttribute("id", DataType = "ID")]
+    public string Id { get; set; }
+
+    [System.Xml.Serialization.XmlAttribute("refs", DataType = "IDREFS")]
+    public string[] Refs { get; set; }
+}