CSHARP-5792: Restore previous RepresentationConverter behavior for decimal.MaxValue and decimal.MinValue. Fix Decimal128.ToDecimal conversion and add checks for Min and MaxValue.

Author: lukasvosyka

src/MongoDB.Bson/ObjectModel/Decimal128.cs

@@ -42,29 +42,17 @@ public struct Decimal128 : IConvertible, IComparable<Decimal128>, IEquatable<Dec
 
         // public static properties
         /// <summary>
-        /// Gets the maximum Decimal128 value.
+        /// Gets the maximum value.
         /// </summary>
         public static Decimal128 MaxValue =>
             __maxValue;
 
         /// <summary>
-        /// Gets the minimum Decimal128 value.
+        /// Gets the minimum value.
         /// </summary>
         public static Decimal128 MinValue =>
             __minValue;
 
-        /// <summary>
-        /// Gets the maximum System.Decimal value.
-        /// </summary>
-        public static Decimal128 MaxDecimalValue =>
-            __maxDecimalValue;
-
-        /// <summary>
-        /// Gets the minimum System.Decimal value.
-        /// </summary>
-        public static Decimal128 MinDecimalValue =>
-            __minDecimalValue;
-
         /// <summary>
         /// Represents negative infinity.
         /// </summary>
@@ -751,6 +739,14 @@ public static byte ToByte(Decimal128 d)
         /// <returns>A <see cref="decimal"/> equivalent to <paramref name="d" />.</returns>
         public static decimal ToDecimal(Decimal128 d)
         {
+            if (d == Decimal128.MaxValue)
+            {
+                return decimal.MaxValue;
+            }
+            else if (d == Decimal128.MinValue)
+            {
+                return decimal.MinValue;
+            }
             if (Flags.IsFirstForm(d._highBits))
             {
                 if (Decimal128.Compare(d, __minDecimalValue) < 0 || Decimal128.Compare(d, __maxDecimalValue) > 0)

src/MongoDB.Bson/Serialization/Options/RepresentationConverter.cs

@@ -78,13 +78,11 @@ obj is RepresentationConverter other &&
         /// <returns>A Decimal.</returns>
         public decimal ToDecimal(Decimal128 value)
         {
-            // comparison against Decimal128.MaxValue remains valid for backwards compat.
-            if (value == Decimal128.MaxValue || value == Decimal128.MaxDecimalValue)
+            if (value == Decimal128.MaxValue)
             {
                 return decimal.MaxValue;
             }
-            // comparison against Decimal128.MinValue remains valid for backwards compat.
-            else if (value == Decimal128.MinValue || value == Decimal128.MinDecimalValue)
+            else if (value == Decimal128.MinValue)
             {
                 return decimal.MinValue;
             }
@@ -168,11 +166,11 @@ public Decimal128 ToDecimal128(decimal value)
         {
             if (value == decimal.MaxValue)
             {
-                return Decimal128.MaxDecimalValue;
+                return Decimal128.MaxValue;
             }
             else if (value == decimal.MinValue)
             {
-                return Decimal128.MinDecimalValue;
+                return Decimal128.MinValue;
             }
 
             // conversion from decimal to Decimal128 is lossless so need to check for overflow or truncation

tests/MongoDB.Bson.Tests/ObjectModel/Decimal128Tests.cs

@@ -76,6 +76,8 @@ public void Decimal(string valueString, string expectedResult)
         [InlineData("1E-99", "0")]
         [InlineData("1E-6111", "0")]
         [InlineData("10000.0000000000000000000000001", "10000.000000000000000000000000")] // see: CSHARP-2001
+        [InlineData("9999999999999999999999999999999999E+6111", "79228162514264337593543950335")] // see: CSHARP-5792
+        [InlineData("-9999999999999999999999999999999999E+6111", "-79228162514264337593543950335")]
         public void ToDecimal_should_return_expected_result(string valueString, string expectedResultString)
         {
             var subject = Decimal128.Parse(valueString);

tests/MongoDB.Bson.Tests/Serialization/Options/RepresentationConverterTests.cs

@@ -123,10 +123,9 @@ public void TestConversions()
             // general decimal <-> Decimal128 checks
             Assert.Equal(123.45m, converter.ToDecimal(new Decimal128(123.45m)));
             Assert.Equal(-123.45m, converter.ToDecimal(new Decimal128(-123.45m)));
-            Assert.Equal(Decimal128.MaxDecimalValue, converter.ToDecimal128(decimal.MaxValue));
-            Assert.Equal(Decimal128.MinDecimalValue, converter.ToDecimal128(decimal.MinValue));
-            Assert.Equal(decimal.MaxValue, converter.ToDecimal(Decimal128.MaxDecimalValue));
-            Assert.Equal(decimal.MinValue, converter.ToDecimal(Decimal128.MinDecimalValue));
+            // System.Decimal should be mapped to Decimal128.MaxValue and vice versa
+            Assert.Equal(Decimal128.MaxValue, converter.ToDecimal128(decimal.MaxValue));
+            Assert.Equal(Decimal128.MinValue, converter.ToDecimal128(decimal.MinValue));
             Assert.Equal(decimal.MaxValue, converter.ToDecimal(Decimal128.MaxValue));
             Assert.Equal(decimal.MinValue, converter.ToDecimal(Decimal128.MinValue));
         }