Fix forwarded double attribute parameters

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

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Globalization;
 using System.Linq;
 using CommunityToolkit.Mvvm.SourceGenerators.Helpers;
 using Microsoft.CodeAnalysis;
@@ -89,7 +90,13 @@ public override ExpressionSyntax GetSyntax()
                 {
                     byte b => Literal(b),
                     char c => Literal(c),
-                    double d => Literal(d),
+
+                    // For doubles, we need to manually format it and always add the trailing "D" suffix.
+                    // This ensures that the correct type is produced if the expression was assigned to
+                    // an object (eg. the literal was used in an attribute object parameter/property).
+                    double d => Literal(d.ToString("R", CultureInfo.InvariantCulture) + "D", d),
+
+                    // For floats, Roslyn will automatically add the "F" suffix, so no extra work is needed
                     float f => Literal(f),
                     int i => Literal(i),
                     long l => Literal(l),

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

@@ -94,6 +94,105 @@ public string Name
         VerifyGenerateSources(source, new[] { new ObservablePropertyGenerator() }, ("MyApp.MyViewModel.g.cs", result));
     }
 
+    // See https://github.com/CommunityToolkit/dotnet/issues/601
+    [TestMethod]
+    public void ObservablePropertyWithForwardedAttributesWithNumberLiterals_PreservesType()
+    {
+        string source = """
+            using System.ComponentModel;
+            using CommunityToolkit.Mvvm.ComponentModel;
+
+            #nullable enable
+
+            namespace MyApp;
+
+            partial class MyViewModel : ObservableObject
+            {
+                const double MyDouble = 3.14;
+                const float MyFloat = 3.14f;
+
+                [ObservableProperty]
+                [property: DefaultValue(0.0)]
+                [property: DefaultValue(1.24)]
+                [property: DefaultValue(0.0f)]
+                [property: DefaultValue(0.0f)]
+                [property: DefaultValue(MyDouble)]
+                [property: DefaultValue(MyFloat)]
+                private object? a;
+            }
+
+            public class DefaultValueAttribute : Attribute
+            {
+                public DefaultValueAttribute(object value)
+                {
+                }
+            }
+            """;
+
+        string result = """
+            // <auto-generated/>
+            #pragma warning disable
+            #nullable enable
+            namespace MyApp
+            {
+                partial class MyViewModel
+                {
+                    /// <inheritdoc cref="a"/>
+                    [global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", "8.1.0.0")]
+                    [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+                    [global::MyApp.DefaultValueAttribute(0D)]
+                    [global::MyApp.DefaultValueAttribute(1.24D)]
+                    [global::MyApp.DefaultValueAttribute(0F)]
+                    [global::MyApp.DefaultValueAttribute(0F)]
+                    [global::MyApp.DefaultValueAttribute(3.14D)]
+                    [global::MyApp.DefaultValueAttribute(3.14F)]
+                    public object? A
+                    {
+                        get => a;
+                        set
+                        {
+                            if (!global::System.Collections.Generic.EqualityComparer<object?>.Default.Equals(a, value))
+                            {
+                                OnAChanging(value);
+                                OnAChanging(default, value);
+                                OnPropertyChanging(global::CommunityToolkit.Mvvm.ComponentModel.__Internals.__KnownINotifyPropertyChangingArgs.A);
+                                a = value;
+                                OnAChanged(value);
+                                OnAChanged(default, value);
+                                OnPropertyChanged(global::CommunityToolkit.Mvvm.ComponentModel.__Internals.__KnownINotifyPropertyChangedArgs.A);
+                            }
+                        }
+                    }
+
+                    /// <summary>Executes the logic for when <see cref="A"/> is changing.</summary>
+                    /// <param name="value">The new property value being set.</param>
+                    /// <remarks>This method is invoked right before the value of <see cref="A"/> is changed.</remarks>
+                    [global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", "8.1.0.0")]
+                    partial void OnAChanging(object? value);
+                    /// <summary>Executes the logic for when <see cref="A"/> is changing.</summary>
+                    /// <param name="oldValue">The previous property value that is being replaced.</param>
+                    /// <param name="newValue">The new property value being set.</param>
+                    /// <remarks>This method is invoked right before the value of <see cref="A"/> is changed.</remarks>
+                    [global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", "8.1.0.0")]
+                    partial void OnAChanging(object? oldValue, object? newValue);
+                    /// <summary>Executes the logic for when <see cref="A"/> just changed.</summary>
+                    /// <param name="value">The new property value that was set.</param>
+                    /// <remarks>This method is invoked right after the value of <see cref="A"/> is changed.</remarks>
+                    [global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", "8.1.0.0")]
+                    partial void OnAChanged(object? value);
+                    /// <summary>Executes the logic for when <see cref="A"/> just changed.</summary>
+                    /// <param name="oldValue">The previous property value that was replaced.</param>
+                    /// <param name="newValue">The new property value that was set.</param>
+                    /// <remarks>This method is invoked right after the value of <see cref="A"/> is changed.</remarks>
+                    [global::System.CodeDom.Compiler.GeneratedCode("CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator", "8.1.0.0")]
+                    partial void OnAChanged(object? oldValue, object? newValue);
+                }
+            }
+            """;
+
+        VerifyGenerateSources(source, new[] { new ObservablePropertyGenerator() }, ("MyApp.MyViewModel.g.cs", result));
+    }
+
     /// <summary>
     /// Generates the requested sources
     /// </summary>