fix enums could not be cast to decimal (#576)

* fix enums could not be cast to decimal

* add test for enums and decimal/double

Author: jogibear9988

src/System.Linq.Dynamic.Core/Parser/ExpressionPromoter.cs

@@ -105,7 +105,11 @@ public virtual Expression Promote(Expression expr, Type type, bool exact, bool c
 
             if (TypeHelper.IsCompatibleWith(expr.Type, type))
             {
-                if (type.GetTypeInfo().IsValueType || exact || expr.Type.GetTypeInfo().IsValueType && convertExpr)
+                if (type == typeof(decimal) && expr.Type.IsEnum)
+                {
+                    return Expression.Convert(Expression.Convert(expr, Enum.GetUnderlyingType(expr.Type)), type);
+                }
+                else if (type.GetTypeInfo().IsValueType || exact || expr.Type.GetTypeInfo().IsValueType && convertExpr)
                 {
                     return Expression.Convert(expr, type);
                 }

test/System.Linq.Dynamic.Core.Tests/ExpressionTests.cs

@@ -681,12 +681,24 @@ public void ExpressionTests_Enum_Property_Equality_Using_Argument()
             var resultEqualIntParamLeft = qry.Where("@0 == it.B", 1).ToDynamicArray();
             var resultEqualIntParamRight = qry.Where("it.B == @0", 1).ToDynamicArray();
 
+            var resultEqualDecimalParamLeft = qry.Where("@0 == it.B", 1m).ToDynamicArray();
+            var resultEqualDecimalParamRight = qry.Where("it.B == @0", 1m).ToDynamicArray();
+
+            var resultEqualDoubleParamLeft = qry.Where("@0 == it.B", 1.0).ToDynamicArray();
+            var resultEqualDoubleParamRight = qry.Where("it.B == @0", 1.0).ToDynamicArray();
+
             // Assert
             Check.That(resultEqualEnumParamLeft.Single()).Equals(TestEnum2.Var2);
             Check.That(resultEqualEnumParamRight.Single()).Equals(TestEnum2.Var2);
 
             Check.That(resultEqualIntParamLeft.Single()).Equals(TestEnum2.Var2);
             Check.That(resultEqualIntParamRight.Single()).Equals(TestEnum2.Var2);
+
+            Check.That(resultEqualDecimalParamLeft.Single()).Equals(TestEnum2.Var2);
+            Check.That(resultEqualDecimalParamRight.Single()).Equals(TestEnum2.Var2);
+
+            Check.That(resultEqualDoubleParamLeft.Single()).Equals(TestEnum2.Var2);
+            Check.That(resultEqualDoubleParamRight.Single()).Equals(TestEnum2.Var2);
         }
 
         [Fact]