[Fix 3.1] Remove union overlay design and use reflection in SqlTypeWorkarounds (#1699)

Porting #1647 to 3.1-servicing.

Author: David-Engel

src/Microsoft.Data.SqlClient/netcore/src/Microsoft.Data.SqlClient.csproj

@@ -537,6 +537,7 @@
     <Compile Include="Microsoft\Data\SqlClient\SNI\SspiClientContextStatus.cs" />
     <Compile Include="Microsoft\Data\SqlClient\SNI\SSRP.cs" />
     <Compile Include="Microsoft\Data\SqlClient\TdsParserStateObjectManaged.cs" />
+    <Compile Include="Microsoft\Data\SqlTypes\SqlTypeWorkarounds.netcore.cs" />
     <Compile Include="Interop\SNINativeMethodWrapper.Common.cs" />
     <Compile Include="Microsoft\Data\SqlClient\AlwaysEncryptedHelperClasses.cs" />
     <Compile Include="Microsoft\Data\SqlClient\SqlQueryMetadataCache.cs" />

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlTypes/SqlTypeWorkarounds.netcore.cs

@@ -0,0 +1,152 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Data.SqlTypes;
+using System.Runtime.InteropServices;
+
+namespace Microsoft.Data.SqlTypes
+{
+    /// <summary>
+    /// This type provides workarounds for the separation between System.Data.Common
+    /// and Microsoft.Data.SqlClient.  The latter wants to access internal members of the former, and
+    /// this class provides ways to do that.  We must review and update this implementation any time the
+    /// implementation of the corresponding types in System.Data.Common change.
+    /// </summary>
+    internal static partial class SqlTypeWorkarounds
+    {
+        #region Work around inability to access SqlMoney.ctor(long, int) and SqlMoney.ToSqlInternalRepresentation
+        /// <summary>
+        /// Constructs a SqlMoney from a long value without scaling. The ignored parameter exists
+        /// only to distinguish this constructor from the constructor that takes a long.
+        /// Used only internally.
+        /// </summary>
+        internal static SqlMoney SqlMoneyCtor(long value, int ignored)
+        {
+            var c = default(SqlMoneyCaster);
+
+            // Same behavior as the internal SqlMoney.ctor(long, bool) overload
+            c.Fake._fNotNull = true;
+            c.Fake._value = value;
+
+            return c.Real;
+        }
+
+        internal static long SqlMoneyToSqlInternalRepresentation(SqlMoney money)
+        {
+            var c = default(SqlMoneyCaster);
+            c.Real = money;
+
+            // Same implementation as the internal SqlMoney.ToSqlInternalRepresentation implementation
+            if (money.IsNull)
+            {
+                throw new SqlNullValueException();
+            }
+            return c.Fake._value;
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct SqlMoneyLookalike // exact same shape as SqlMoney, but with accessible fields
+        {
+            internal bool _fNotNull;
+            internal long _value;
+        }
+
+        [StructLayout(LayoutKind.Explicit)]
+        private struct SqlMoneyCaster
+        {
+            [FieldOffset(0)]
+            internal SqlMoney Real;
+            [FieldOffset(0)]
+            internal SqlMoneyLookalike Fake;
+        }
+        #endregion
+
+        #region Work around inability to access SqlDecimal._data1/2/3/4
+        internal static void SqlDecimalExtractData(SqlDecimal d, out uint data1, out uint data2, out uint data3, out uint data4)
+        {
+            // Extract the four data elements from SqlDecimal.
+            var c = default(SqlDecimalCaster);
+            c.Real = d;
+            data1 = c.Fake._data1;
+            data2 = c.Fake._data2;
+            data3 = c.Fake._data3;
+            data4 = c.Fake._data4;
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct SqlDecimalLookalike // exact same shape as SqlDecimal, but with accessible fields
+        {
+            internal byte _bStatus;
+            internal byte _bLen;
+            internal byte _bPrec;
+            internal byte _bScale;
+            internal uint _data1;
+            internal uint _data2;
+            internal uint _data3;
+            internal uint _data4;
+        }
+
+        [StructLayout(LayoutKind.Explicit)]
+        private struct SqlDecimalCaster
+        {
+            [FieldOffset(0)]
+            internal SqlDecimal Real;
+            [FieldOffset(0)]
+            internal SqlDecimalLookalike Fake;
+        }
+        #endregion
+
+        #region Work around inability to access SqlBinary.ctor(byte[], bool)
+        internal static SqlBinary SqlBinaryCtor(byte[] value, bool ignored)
+        {
+            // Construct a SqlBinary without allocating/copying the byte[].  This provides
+            // the same behavior as SqlBinary.ctor(byte[], bool).
+            var c = default(SqlBinaryCaster);
+            c.Fake._value = value;
+            return c.Real;
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct SqlBinaryLookalike
+        {
+            internal byte[] _value;
+        }
+
+        [StructLayout(LayoutKind.Explicit)]
+        private struct SqlBinaryCaster
+        {
+            [FieldOffset(0)]
+            internal SqlBinary Real;
+            [FieldOffset(0)]
+            internal SqlBinaryLookalike Fake;
+        }
+        #endregion
+
+        #region Work around inability to access SqlGuid.ctor(byte[], bool)
+        internal static SqlGuid SqlGuidCtor(byte[] value, bool ignored)
+        {
+            // Construct a SqlGuid without allocating/copying the byte[].  This provides
+            // the same behavior as SqlGuid.ctor(byte[], bool).
+            var c = default(SqlGuidCaster);
+            c.Fake._value = value;
+            return c.Real;
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct SqlGuidLookalike
+        {
+            internal byte[] _value;
+        }
+
+        [StructLayout(LayoutKind.Explicit)]
+        private struct SqlGuidCaster
+        {
+            [FieldOffset(0)]
+            internal SqlGuid Real;
+            [FieldOffset(0)]
+            internal SqlGuidLookalike Fake;
+        }
+        #endregion
+    }
+}

src/Microsoft.Data.SqlClient/netfx/src/Microsoft.Data.SqlClient.csproj

@@ -505,6 +505,7 @@
     <Compile Include="Microsoft\Data\SqlClient\TdsParserStaticMethods.cs" />
     <Compile Include="Microsoft\Data\SqlClient\SqlClientWrapperSmiStreamChars.cs" />
     <Compile Include="Microsoft\Data\SqlTypes\SqlStreamChars.cs" />
+    <Compile Include="Microsoft\Data\SqlTypes\SqlTypeWorkarounds.netfx.cs" />
     <Compile Include="Microsoft\Data\Common\NativeMethods.cs" />
     <Compile Include="Microsoft\Data\Common\GreenMethods.cs" />
     <Compile Include="Microsoft\Data\Common\SQLResource.cs" />