Merge pull request #42 from icsharpcode/avoid-loss-of-precision

Avoid loss of precision after conversion using "/" or integer doubles

ICSharpCode.CodeConverter/CSharp/NodesVisitor.cs

@@ -782,13 +782,13 @@ namespace ICSharpCode.CodeConverter.CSharp
                 if (node.Token.Value == null) {
                     var type = semanticModel.GetTypeInfo(node).ConvertedType;
                     if (type == null) {
-                        return Literal(null)
+                        return Literal("null", null)
                             .WithTrailingTrivia(
                                 SyntaxFactory.Comment("/* TODO Change to default(_) if this is not a reference type */"));
                     }
-                    return !type.IsReferenceType ? SyntaxFactory.DefaultExpression(SyntaxFactory.ParseTypeName(type.ToMinimalDisplayString(semanticModel, node.SpanStart))) : Literal(null);
+                    return !type.IsReferenceType ? SyntaxFactory.DefaultExpression(SyntaxFactory.ParseTypeName(type.ToMinimalDisplayString(semanticModel, node.SpanStart))) : Literal("null", null);
                 }
-                return Literal(node.Token.Value);
+                return Literal(node.Token.Text, node.Token.Value);
             }
 
             public override CSharpSyntaxNode VisitInterpolatedStringExpression(VBSyntax.InterpolatedStringExpressionSyntax node)
@@ -1230,13 +1230,30 @@ namespace ICSharpCode.CodeConverter.CSharp
                         return SyntaxFactory.BinaryExpression(SyntaxKind.NotEqualsExpression, otherArgument, SyntaxFactory.LiteralExpression(SyntaxKind.NullLiteralExpression));
                     }
                 }
+
                 var kind = ConvertToken(VBasic.VisualBasicExtensions.Kind(node), TokenContext.Local);
-                return SyntaxFactory.BinaryExpression(
-                    kind,
-                    (ExpressionSyntax)node.Left.Accept(TriviaConvertingVisitor),
-                    SyntaxFactory.Token(CSharpUtil.GetExpressionOperatorTokenKind(kind)),
-                    (ExpressionSyntax)node.Right.Accept(TriviaConvertingVisitor)
-                );
+                var lhs = (ExpressionSyntax)node.Left.Accept(TriviaConvertingVisitor);
+                var op = SyntaxFactory.Token(CSharpUtil.GetExpressionOperatorTokenKind(kind));
+                var rhs = (ExpressionSyntax)node.Right.Accept(TriviaConvertingVisitor);
+
+                // VB DivideExpression "/" is always on doubles unless you use the "\" IntegerDivideExpression, so need to cast in C#
+                // Need the unconverted type, since the whole point is that it gets converted to a double by the operator
+                if (node.IsKind(VBasic.SyntaxKind.DivideExpression) && !HasOperandOfUnconvertedType(node, "System.Double")) {
+                    var doubleType = SyntaxFactory.PredefinedType(SyntaxFactory.Token(SyntaxKind.DoubleKeyword));
+                    rhs = SyntaxFactory.CastExpression(doubleType, rhs);
+                }
+                
+                return SyntaxFactory.BinaryExpression(kind, lhs, op, rhs);
+            }
+
+            private bool HasOperandOfUnconvertedType(VBSyntax.BinaryExpressionSyntax node, string operandType)
+            {
+                return new[] {node.Left, node.Right}.Any(e => UnconvertedIsType(e, operandType));
+            }
+
+            private bool UnconvertedIsType(VBSyntax.ExpressionSyntax e, string fullTypeName)
+            {
+                return semanticModel.GetTypeInfo(e).Type?.GetFullMetadataName() == fullTypeName;
             }
 
             public override CSharpSyntaxNode VisitInvocationExpression(VBSyntax.InvocationExpressionSyntax node)

ICSharpCode.CodeConverter/CSharp/VisualBasicConverter.cs

@@ -80,9 +80,9 @@ namespace ICSharpCode.CodeConverter.CSharp
             return newDecls;
         }
 
-        static ExpressionSyntax Literal(object o) => GetLiteralExpression(o);
+        static ExpressionSyntax Literal(string valueText, object o) => GetLiteralExpression(valueText, o);
 
-        internal static ExpressionSyntax GetLiteralExpression(object value)
+        internal static ExpressionSyntax GetLiteralExpression(string valueText, object value)
         {
             if (value is bool)
                 return SyntaxFactory.LiteralExpression((bool)value ? SyntaxKind.TrueLiteralExpression : SyntaxKind.FalseLiteralExpression);
@@ -105,10 +105,14 @@ namespace ICSharpCode.CodeConverter.CSharp
 
             if (value is float)
                 return SyntaxFactory.LiteralExpression(SyntaxKind.NumericLiteralExpression, SyntaxFactory.Literal((float)value));
-            if (value is double)
-                return SyntaxFactory.LiteralExpression(SyntaxKind.NumericLiteralExpression, SyntaxFactory.Literal((double)value));
-            if (value is decimal)
+            if (value is double) {
+                // Important to use value text, otherwise "10.0" gets coerced to and integer literal of 10 which can change semantics
+                return SyntaxFactory.LiteralExpression(SyntaxKind.NumericLiteralExpression, SyntaxFactory.Literal(valueText, (double)value));
+            }
+            if (value is decimal) {
+                // Don't use value text - it has a "D" in VB, but an "M" in C#
                 return SyntaxFactory.LiteralExpression(SyntaxKind.NumericLiteralExpression, SyntaxFactory.Literal((decimal)value));
+            }
 
             if (value is char)
                 return SyntaxFactory.LiteralExpression(SyntaxKind.CharacterLiteralExpression, SyntaxFactory.Literal((char)value));

Tests/CSharp/ExpressionTests.cs

@@ -104,6 +104,28 @@ End Class", @"class TestClass
 }");
         }
 
+        [Fact]
+        public void FloatingPointDivisionIsForced()
+        {
+            TestConversionVisualBasicToCSharp(@"Class TestClass
+    Private Sub TestMethod()
+        Dim x = 10 / 3
+        x /= 2
+        Dim y = 10.0 / 3
+        y /= 2
+    End Sub
+End Class", @"class TestClass
+{
+    private void TestMethod()
+    {
+        var x = 10 / (double)3;
+        x /= 2;
+        var y = 10.0 / 3;
+        y /= 2;
+    }
+}");
+        }
+
         [Fact]
         public void FullyTypeInferredEnumerableCreation()
         {
@@ -482,7 +504,7 @@ class TestClass
         var test2 = (a, b) =>
         {
             if (b > 0)
-                return a / b;
+                return a / (double)b;
             return 0;
         };