Re-fix #160 (#255)

+semver:fix

Author: hazzik

src/DelegateDecompiler.Tests/EnumTests.cs

@@ -59,7 +59,7 @@ public void TestEnumPropertyEqualsFooOrElseEnumPropertyEqualsBar()
             Test(expected1, expected2, compiled);
         }
 
-        [Test, Ignore("Not fixed yet")]
+        [Test]
         public void TestEnumPropertyIsFooOrBar()
         {
             Expression<Func<TestEnum, bool>> expected = x => (int)x <= 1;
@@ -311,11 +311,11 @@ public void Issue98B()
             Test(expected, compiled);
         }
 
-        [Test, Ignore("Not fixed yet")]
+        [Test]
         public void Issue160()
         {
             Expression<Func<int?, bool>> expected1 = x => (TestEnum?)x == TestEnum.Bar;
-            Expression<Func<int?, bool>> expected2 = x => (x.HasValue ? (TestEnum?)(x ?? 0) : null) == TestEnum.Bar;
+            Expression<Func<int?, bool>> expected2 = x => (int)((TestEnum?)x ?? TestEnum.Foo) == 1;
             Func<int?, bool> compiled = x => (TestEnum?)x == TestEnum.Bar;
             Test(expected1, expected2, compiled);
         }

src/DelegateDecompiler/OptimizeExpressionVisitor.cs

@@ -14,6 +14,7 @@ protected override Expression VisitNew(NewExpression node)
             {
                 return Expression.Convert(Visit(node.Arguments[0]), node.Type);
             }
+
             return base.VisitNew(node);
         }
 
@@ -45,10 +46,21 @@ protected override Expression VisitConditional(ConditionalExpression node)
                 return boolValue ? ifTrue : ifFalse;
             }
 
-            if (IsCoalesce(test, ifTrue, out var expression))
+            if (IsCoalesce(test, UnwrapConvertToNullable(ifTrue), out var expression))
             {
+                if (IsNullConstant(ifFalse))
+                {
+                    if (expression.Type != node.Type)
+                    {
+                        expression = Expression.Convert(expression, node.Type);
+                    }
+
+                    return expression;
+                }
+
                 return Expression.Coalesce(expression, ifFalse);
             }
+
             var ifTrueBinary = UnwrapConvertToNullable(ifTrue) as BinaryExpression;
             if (ifTrueBinary != null)
             {
@@ -112,6 +124,11 @@ protected override Expression VisitConditional(ConditionalExpression node)
             return node.Update(test, ifTrue, ifFalse);
         }
 
+        static bool IsNullConstant(Expression expression)
+        {
+            return expression is ConstantExpression constant && constant.Value == null;
+        }
+
         private static bool TryConvert(ConstantExpression constant, BinaryExpression left, Expression right, out BinaryExpression result, bool isLeft)
         {
             if (constant?.Value is bool booleanValue)
@@ -237,11 +254,13 @@ static Expression ConvertToNullable(Expression expression)
 
         static Expression UnwrapConvertToNullable(Expression expression)
         {
-            var unary = expression as UnaryExpression;
-            if (unary != null && expression.NodeType == ExpressionType.Convert && expression.Type.IsNullableType())
+            if (expression is UnaryExpression unary &&
+                expression.NodeType == ExpressionType.Convert &&
+                expression.Type.IsNullableType())
             {
                 return unary.Operand;
             }
+
             return expression;
         }
 
@@ -261,9 +280,8 @@ static bool ExtractNullableArgument(Expression hasValue, Expression getValueOrDe
 
         static bool IsCoalesce(Expression hasValue, Expression getValueOrDefault, out Expression expression)
         {
-            MemberExpression memberExpression;
-            MethodCallExpression callExpression;
-            if (IsHasValue(hasValue, out memberExpression) && IsGetValueOrDefault(getValueOrDefault, out callExpression))
+            if (IsHasValue(hasValue, out var memberExpression) &&
+                IsGetValueOrDefault(getValueOrDefault, out var callExpression))
             {
                 expression = memberExpression.Expression;
                 if (expression == callExpression.Object)

src/DelegateDecompiler/Processor.cs

@@ -397,7 +397,7 @@ Expression Process()
                              state.Instruction.OpCode == OpCodes.Bgt_Un_S)
                     {
                         var val1 = state.Stack.Pop();
-                        state.Instruction = ConditionalBranch(state, val => Expression.GreaterThan(val, val1));
+                        state.Instruction = ConditionalBranch(state, val => MakeBinaryExpression(val, val1, ExpressionType.GreaterThan));
                         continue;
                     }
                     else if (state.Instruction.OpCode == OpCodes.Bge ||
@@ -406,7 +406,7 @@ Expression Process()
                              state.Instruction.OpCode == OpCodes.Bge_Un_S)
                     {
                         var val1 = state.Stack.Pop();
-                        state.Instruction = ConditionalBranch(state, val => Expression.GreaterThanOrEqual(val, val1));
+                        state.Instruction = ConditionalBranch(state, val => MakeBinaryExpression(val, val1, ExpressionType.GreaterThanOrEqual));
                         continue;
                     }
                     else if (state.Instruction.OpCode == OpCodes.Blt ||
@@ -415,7 +415,7 @@ Expression Process()
                              state.Instruction.OpCode == OpCodes.Blt_Un_S)
                     {
                         var val1 = state.Stack.Pop();
-                        state.Instruction = ConditionalBranch(state, val => Expression.LessThan(val, val1));
+                        state.Instruction = ConditionalBranch(state, val => MakeBinaryExpression(val, val1, ExpressionType.LessThan));
                         continue;
                     }
                     else if (state.Instruction.OpCode == OpCodes.Ble ||