Fix forwarding enum values with negative values in attributes

src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/Models/TypedConstantInfo.cs

@@ -135,8 +135,17 @@ public sealed record Enum(string TypeName, object Value) : TypedConstantInfo
         public override ExpressionSyntax GetSyntax()
         {
             // We let Roslyn parse the value expression, so that it can automatically handle both positive and negative values. This
-            // is needed because negative values have a different syntax tree (UnaryMinuxExpression holding the numeric expression).
-            return CastExpression(IdentifierName(TypeName), ParseExpression(Value.ToString()));
+            // is needed because negative values have a different syntax tree (UnaryMinusExpression holding the numeric expression).
+            ExpressionSyntax valueExpression = ParseExpression(Value.ToString());
+
+            // If the value is negative, we have to put parentheses around them (to avoid CS0075 errors)
+            if (valueExpression is PrefixUnaryExpressionSyntax unaryExpression && unaryExpression.IsKind(SyntaxKind.UnaryMinusExpression))
+            {
+                valueExpression = ParenthesizedExpression(valueExpression);
+            }
+
+            // Now we can safely return the cast expression for the target enum type (with optional parentheses if needed)
+            return CastExpression(IdentifierName(TypeName), valueExpression);
         }
     }
 

tests/CommunityToolkit.Mvvm.SourceGenerators.UnitTests/Test_SourceGeneratorsCodegen.cs

@@ -1349,10 +1349,10 @@ partial class MyViewModel
                     /// <inheritdoc cref="a"/>
                     [global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", <ASSEMBLY_VERSION>)]
                     [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)-1073741824)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)-9223372036854775808)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)-1234)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)-1)]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)(-1073741824))]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)(-9223372036854775808))]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)(-1234))]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)(-1))]
                     public object? A
                     {
                         get => a;
@@ -1489,24 +1489,24 @@ partial class MyViewModel
                     [global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", <ASSEMBLY_VERSION>)]
                     [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)0)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)-1073741824)]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)(-1073741824))]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)42)]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)456)]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)123)]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)0)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)-9223372036854775808)]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)(-9223372036854775808))]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)42)]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)456)]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)123)]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)1)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)-1234)]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)(-1234))]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)42)]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)456)]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)123)]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)1)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)-1)]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)(-1))]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)42)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)-56)]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)(-56))]
                     [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)123)]
                     public object? A
                     {
@@ -1792,18 +1792,18 @@ partial class MyViewModel
                 {
                     /// <summary>The backing field for <see cref="TestCommand"/>.</summary>
                     [global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.RelayCommandGenerator", <ASSEMBLY_VERSION>)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)-1073741824)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)-9223372036854775808)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)-1234)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)-1)]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)(-1073741824))]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)(-9223372036854775808))]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)(-1234))]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)(-1))]
                     private global::CommunityToolkit.Mvvm.Input.RelayCommand? testCommand;
                     /// <summary>Gets an <see cref="global::CommunityToolkit.Mvvm.Input.IRelayCommand"/> instance wrapping <see cref="Test"/>.</summary>
                     [global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.RelayCommandGenerator", <ASSEMBLY_VERSION>)]
                     [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)-1073741824)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)-9223372036854775808)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)-1234)]
-                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)-1)]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum1)(-1073741824))]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum2)(-9223372036854775808))]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum3)(-1234))]
+                    [global::MyApp.DefaultValueAttribute((global::MyApp.NegativeEnum4)(-1))]
                     public global::CommunityToolkit.Mvvm.Input.IRelayCommand TestCommand => testCommand ??= new global::CommunityToolkit.Mvvm.Input.RelayCommand(new global::System.Action(Test));
                 }
             }

tests/CommunityToolkit.Mvvm.UnitTests/Test_ObservablePropertyAttribute.cs

@@ -1051,6 +1051,23 @@ public void Test_ObservableProperty_MemberNotNullAttributeIsPresent()
     }
 #endif
 
+    // See https://github.com/CommunityToolkit/dotnet/issues/731
+    [TestMethod]
+    public void Test_ObservableProperty_ForwardedAttributesWithNegativeValues()
+    {
+        Assert.AreEqual(PositiveEnum.Something,
+            typeof(ModelWithForwardedAttributesWithNegativeValues)
+            .GetProperty(nameof(ModelWithForwardedAttributesWithNegativeValues.Test2))!
+            .GetCustomAttribute<DefaultValueAttribute>()!
+            .Value);
+
+        Assert.AreEqual(NegativeEnum.Problem,
+            typeof(ModelWithForwardedAttributesWithNegativeValues)
+            .GetProperty(nameof(ModelWithForwardedAttributesWithNegativeValues.Test3))!
+            .GetCustomAttribute<DefaultValueAttribute>()!
+            .Value);
+    }
+
     public abstract partial class BaseViewModel : ObservableObject
     {
         public string? Content { get; set; }
@@ -1693,4 +1710,39 @@ public ModelWithNonNullableObservableProperty()
         internal string name;
     }
 #endif
+
+    private partial class ModelWithForwardedAttributesWithNegativeValues : ObservableObject
+    {
+        [ObservableProperty]
+        private bool _test1;
+
+        [ObservableProperty]
+        [property: DefaultValue(PositiveEnum.Something)]
+        private PositiveEnum _test2;
+
+        [ObservableProperty]
+        [property: DefaultValue(NegativeEnum.Problem)]
+        private NegativeEnum _test3;
+
+        [ObservableProperty]
+        private int _test4;
+
+        public ModelWithForwardedAttributesWithNegativeValues()
+        {
+            Test1 = true;
+            Test2 = PositiveEnum.Else;
+        }
+    }
+
+    public enum PositiveEnum
+    {
+        Something = 0,
+        Else = 1
+    }
+
+    public enum NegativeEnum
+    {
+        Problem = -1,
+        OK = 0
+    }
 }