Fix conditional expressions for classes with a common ancestor

src/DelegateDecompiler.Tests/Employee.cs

@@ -19,27 +19,18 @@ public class Employee
         public int To;
 
         [Computed]
-        public string FullName
-        {
-            get { return FirstName + " " + LastName; }
-        }
+        public string FullName => FirstName + " " + LastName;
 
-        public string FullNameWithoutAttribute
-        {
-            get { return FirstName + " " + LastName; }
-        }
+        public string FullNameWithoutAttribute => FirstName + " " + LastName;
 
         [Computed]
-        public string FromTo
-        {
-            get { return From + "-" + To; }
-        }
+        public string FromTo => From + "-" + To;
 
         [Computed]
-        public bool IsActive
-        {
-            get { return true; }
-        }
+        public bool IsActive => true;
+
+        [Computed]
+        public IEmployeeStatus Status => IsActive ? (IEmployeeStatus)new Active() : new Terminated();
 
         [Computed]
         public int Count
@@ -151,4 +142,16 @@ public static string FullName(this Employee e)
             return e.FirstName + " " + e.LastName;
         }
     }
+
+    public interface IEmployeeStatus
+    {
+    }
+
+    public class Active : IEmployeeStatus
+    {
+    }
+
+    public class Terminated : IEmployeeStatus
+    {
+    }
 }

src/DelegateDecompiler.Tests/QueryableExtensionsTests.cs

@@ -352,5 +352,21 @@ public void Issue78()
 
             AssertAreEqual(expected.Expression, actual.Expression);
         }
+
+        [Test]
+        public void Issue127()
+        {
+            var employees = new[] { new Employee { FirstName = "Test", LastName = "User" } };
+
+            var expected = (from employee in employees.AsQueryable()
+                where ((IEmployeeStatus)new Active()) is Active
+                select employee);
+
+            var actual = (from employee in employees.AsQueryable()
+                where employee.Status is Active
+                select employee).Decompile();
+
+            AssertAreEqual(expected.Expression, actual.Expression);
+        }
     }
 }

src/DelegateDecompiler/Address.cs

@@ -27,7 +27,7 @@ public Address Clone(IDictionary<Address, Address> map)
         {
             if (map.ContainsKey(this))
                 return map[this];
-            var result = new Address() { Expression = this.Expression };
+            var result = new Address { Expression = this.Expression };
             map[this] = result;
             return result;
         }

src/DelegateDecompiler/DecompiledQueryProvider.cs

@@ -40,19 +40,19 @@ public virtual IQueryable CreateQuery(Expression expression)
 
         public virtual IQueryable<TElement> CreateQuery<TElement>(Expression expression)
         {
-            var decompiled = expression.Decompile();
+            var decompiled = expression.Decompile().Optimize();
             return new DecompiledQueryable<TElement>(this, Inner.CreateQuery<TElement>(decompiled));
         }
 
         public object Execute(Expression expression)
         {
-            var decompiled = expression.Decompile();
+            var decompiled = expression.Decompile().Optimize();
             return Inner.Execute(decompiled);
         }
 
         public TResult Execute<TResult>(Expression expression)
         {
-            var decompiled = expression.Decompile();
+            var decompiled = expression.Decompile().Optimize();
             return Inner.Execute<TResult>(decompiled);
         }
     }

src/DelegateDecompiler/OptimizeExpressionVisitor.cs

@@ -39,6 +39,11 @@ protected override Expression VisitConditional(ConditionalExpression node)
             var test = Visit(node.Test);
             var ifTrue = Visit(node.IfTrue);
             var ifFalse = Visit(node.IfFalse);
+
+            if (test is ConstantExpression constant && constant.Value is bool boolValue)
+            {
+                return boolValue ? ifTrue : ifFalse;
+            }
 
             if (IsCoalesce(test, ifTrue, out var expression))
             {

src/DelegateDecompiler/Processor.cs

@@ -955,43 +955,48 @@ internal static Expression AdjustType(Expression expression, Type type)
                 return expression;
             }
 
-            var constantExpression = expression as ConstantExpression;
-            if (constantExpression != null)
+            if (expression is ConstantExpression constant)
             {
-                if (constantExpression.Value == null)
+                if (constant.Value == null)
                 {
                     return Expression.Constant(null, type);
                 }
 
-                if (constantExpression.Type == typeof(int))
+                if (constant.Type == typeof(int))
                 {
                     if (type.IsEnum)
                     {
-                        return Expression.Constant(Enum.ToObject(type, constantExpression.Value));
+                        return Expression.Constant(Enum.ToObject(type, constant.Value));
                     }
+
                     if (type == typeof(bool))
                     {
-                        return Expression.Constant(Convert.ToBoolean(constantExpression.Value));
+                        return Expression.Constant(Convert.ToBoolean(constant.Value));
                     }
+
                     if (type == typeof(byte))
                     {
-                        return Expression.Constant(Convert.ToByte(constantExpression.Value));
+                        return Expression.Constant(Convert.ToByte(constant.Value));
                     }
+
                     if (type == typeof(sbyte))
                     {
-                        return Expression.Constant(Convert.ToSByte(constantExpression.Value));
+                        return Expression.Constant(Convert.ToSByte(constant.Value));
                     }
+
                     if (type == typeof(short))
                     {
-                        return Expression.Constant(Convert.ToInt16(constantExpression.Value));
+                        return Expression.Constant(Convert.ToInt16(constant.Value));
                     }
+
                     if (type == typeof(ushort))
                     {
-                        return Expression.Constant(Convert.ToUInt16(constantExpression.Value));
+                        return Expression.Constant(Convert.ToUInt16(constant.Value));
                     }
+
                     if (type == typeof(uint))
                     {
-                        return Expression.Constant(Convert.ToUInt32(constantExpression.Value));
+                        return Expression.Constant(Convert.ToUInt32(constant.Value));
                     }
                 }
             }
@@ -1002,6 +1007,7 @@ internal static Expression AdjustType(Expression expression, Type type)
                     return Expression.NotEqual(expression, Expression.Constant(0));
                 }
             }
+
             if (!type.IsAssignableFrom(expression.Type) && expression.Type.IsEnum && expression.Type.GetEnumUnderlyingType() == type)
             {
                 return Expression.Convert(expression, type);
@@ -1420,7 +1426,8 @@ static void LdLoc(ProcessorState state, int index)
         static void StLoc(ProcessorState state, int index)
         {
             var info = state.Locals[index];
-            info.Address = AdjustType(state.Stack.Pop(), info.Type);
+            var expression = AdjustType(state.Stack.Pop(), info.Type);
+            info.Address = expression.Type == info.Type ? expression : Expression.Convert(expression, info.Type);
         }
 
         static void LdArg(ProcessorState state, int index)