Fix MatchingRefApiCompat issues in Serialization libraries (#28552)

* Fixes: System.Xml.XmlSerializer/src/MatchingRefApiCompatBaseline.uap.txt

* fixes System.Xml.XmlSerializer/src/MatchingRefApiCompatBaseline.uapaot.txt

* Fixes: System.Xml.XmlSerializer/src/MatchingRefApiCompatBaseline.netcoreapp.txt

* Fixes: System.Runtime.Serialization.Xml/src/MatchingRefApiCompatBaseline.txt

* Bring back ReadString() as it is used somewhere else

* fix build errors

4 files changed, 6 insertions, 53 deletions

diff --git a/src/System.Private.Xml/src/System/Xml/Serialization/ReflectionXmlSerializationReader.cs b/src/System.Private.Xml/src/System/Xml/Serialization/ReflectionXmlSerializationReader.cs
index 88fc758431..5c81a051bd 100644
--- a/src/System.Private.Xml/src/System/Xml/Serialization/ReflectionXmlSerializationReader.cs
+++ b/src/System.Private.Xml/src/System/Xml/Serialization/ReflectionXmlSerializationReader.cs
@@ -693,7 +693,7 @@ namespace System.Xml.Serialization
                 {
                     if (special.TypeDesc.Kind == TypeKind.Node)
                     {
-                        value = Document.CreateTextNode(ReadString());
+                        value = Document.CreateTextNode(Reader.ReadString());
                     }
                     else
                     {
@@ -706,11 +706,11 @@ namespace System.Xml.Serialization
                     {
                         if (text.Mapping.TypeDesc.CollapseWhitespace)
                         {
-                            value = CollapseWhitespace(ReadString());
+                            value = CollapseWhitespace(Reader.ReadString());
                         }
                         else
                         {
-                            value = ReadString();
+                            value = Reader.ReadString();
                         }
                     }
                     else
@@ -721,7 +721,7 @@ namespace System.Xml.Serialization
                         }
                         else
                         {
-                            value = WritePrimitive(text.Mapping, (state) => ((ReflectionXmlSerializationReader)state).ReadString(), this);
+                            value = WritePrimitive(text.Mapping, (state) => ((ReflectionXmlSerializationReader)state).Reader.ReadString(), this);
                         }
                     }
                 }
@@ -1832,7 +1832,7 @@ namespace System.Xml.Serialization
                         Func<object, string> functor = (state) =>
                         {
                             var reader = (ReflectionXmlSerializationReader)state;
-                            return reader.CollapseWhitespace(reader.ReadString());
+                            return reader.CollapseWhitespace(reader.Reader.ReadString());
                         };
                         o = WriteEnumMethod(enumMapping, functor, this);
                         ReadEndElement();
diff --git a/src/System.Private.Xml/src/System/Xml/Serialization/XmlSchemaImporter.cs b/src/System.Private.Xml/src/System/Xml/Serialization/XmlSchemaImporter.cs
index 6d4dc7c57e..b3d3af2471 100644
--- a/src/System.Private.Xml/src/System/Xml/Serialization/XmlSchemaImporter.cs
+++ b/src/System.Private.Xml/src/System/Xml/Serialization/XmlSchemaImporter.cs
@@ -37,19 +37,6 @@ namespace System.Xml.Serialization
         /// </devdoc>
         public XmlSchemaImporter(XmlSchemas schemas, CodeIdentifiers typeIdentifiers) : base(schemas, CodeGenerationOptions.GenerateProperties, new ImportContext(typeIdentifiers, false)) { }
 
-        /// <include file='doc\XmlSchemaImporter.uex' path='docs/doc[@for="XmlSchemaImporter.XmlSchemaImporter2"]/*' />
-        /// <devdoc>
-        ///    <para>[To be supplied.]</para>
-        /// </devdoc>
-        public XmlSchemaImporter(XmlSchemas schemas, CodeIdentifiers typeIdentifiers, CodeGenerationOptions options) : base(schemas, options, new ImportContext(typeIdentifiers, false)) { }
-
-        /// <include file='doc\XmlSchemaImporter.uex' path='docs/doc[@for="XmlSchemaImporter.XmlSchemaImporter3"]/*' />
-        /// <devdoc>
-        ///    <para>[To be supplied.]</para>
-        /// </devdoc>
-        public XmlSchemaImporter(XmlSchemas schemas, CodeGenerationOptions options, ImportContext context) : base(schemas, options, context) { }
-
-
         /// <include file='doc\XmlSchemaImporter.uex' path='docs/doc[@for="XmlSchemaImporter.ImportDerivedTypeMapping"]/*' />
         /// <devdoc>
         ///    <para>[To be supplied.]</para>
diff --git a/src/System.Private.Xml/src/System/Xml/Serialization/XmlSerializationReader.cs b/src/System.Private.Xml/src/System/Xml/Serialization/XmlSerializationReader.cs
index 17a11a2cf5..3e349e4340 100644
--- a/src/System.Private.Xml/src/System/Xml/Serialization/XmlSerializationReader.cs
+++ b/src/System.Private.Xml/src/System/Xml/Serialization/XmlSerializationReader.cs
@@ -1428,40 +1428,6 @@ namespace System.Xml.Serialization
             Array.Copy(a, b, length);
             return b;
         }
-        // This is copied from Core's XmlReader.ReadString, as it is not exposed in the Contract.
-        protected virtual string ReadString()
-        {
-            if (Reader.ReadState != ReadState.Interactive)
-            {
-                return string.Empty;
-            }
-            Reader.MoveToElement();
-            if (Reader.NodeType == XmlNodeType.Element)
-            {
-                if (Reader.IsEmptyElement)
-                {
-                    return string.Empty;
-                }
-                else if (!Reader.Read())
-                {
-                    throw new InvalidOperationException(SR.Xml_InvalidOperation);
-                }
-                if (Reader.NodeType == XmlNodeType.EndElement)
-                {
-                    return string.Empty;
-                }
-            }
-            string result = string.Empty;
-            while (IsTextualNode(Reader.NodeType))
-            {
-                result += Reader.Value;
-                if (!Reader.Read())
-                {
-                    break;
-                }
-            }
-            return result;
-        }
 
         // 0x6018
         private static uint s_isTextualNodeBitmap = (1 << (int)XmlNodeType.Text) | (1 << (int)XmlNodeType.CDATA) | (1 << (int)XmlNodeType.Whitespace) | (1 << (int)XmlNodeType.SignificantWhitespace);
diff --git a/src/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs b/src/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs
index 25fdb4df57..d9f998ba0f 100644
--- a/src/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs
+++ b/src/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs
@@ -807,7 +807,7 @@ namespace System.Xml.Serialization
 #if !FEATURE_SERIALIZATION_UAPAOT
         [ResourceConsumption(ResourceScope.Machine, ResourceScope.Machine)]
         [ResourceExposure(ResourceScope.None)]
-        public static bool GenerateSerializer(Type[] types, XmlMapping[] mappings, Stream stream)
+        internal static bool GenerateSerializer(Type[] types, XmlMapping[] mappings, Stream stream)
         {
             if (types == null || types.Length == 0)
                 return false;