Add diagnostics for name collision for [ObservableProperty]

Author: Sergio0694

CommunityToolkit.Mvvm.SourceGenerators/AnalyzerReleases.Unshipped.md

@@ -18,3 +18,4 @@ MVVMTK0010 | CommunityToolkit.Mvvm.SourceGenerators.ICommandGenerator | Error |
 MVVMTK0011 | CommunityToolkit.Mvvm.SourceGenerators.ICommandGenerator | Error | See https://aka.ms/mvvmtoolkit/error
 MVVMTK0012 | CommunityToolkit.Mvvm.SourceGenerators.ICommandGenerator | Error | See https://aka.ms/mvvmtoolkit/error
 MVVMTK0013 | CommunityToolkit.Mvvm.SourceGenerators.ICommandGenerator | Error | See https://aka.ms/mvvmtoolkit/error
+MVVMTK0014 | CommunityToolkit.Mvvm.SourceGenerators.ICommandGenerator | Error | See https://aka.ms/mvvmtoolkit/error

CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/ObservablePropertyGenerator.Execute.cs

@@ -46,6 +46,16 @@ public static PropertyInfo GetInfo(IFieldSymbol fieldSymbol, out ImmutableArray<
             string fieldName = fieldSymbol.Name;
             string propertyName = GetGeneratedPropertyName(fieldSymbol);
 
+            // Check for name collisions
+            if (fieldName == propertyName)
+            {
+                builder.Add(
+                    ObservablePropertyNameCollisionError,
+                    fieldSymbol,
+                    fieldSymbol.ContainingType,
+                    fieldSymbol.Name);
+            }
+
             ImmutableArray<string>.Builder propertyChangedNames = ImmutableArray.CreateBuilder<string>();
             ImmutableArray<string>.Builder propertyChangingNames = ImmutableArray.CreateBuilder<string>();
             ImmutableArray<string>.Builder notifiedCommandNames = ImmutableArray.CreateBuilder<string>();

CommunityToolkit.Mvvm.SourceGenerators/Diagnostics/DiagnosticDescriptors.cs

@@ -219,4 +219,20 @@ internal static class DiagnosticDescriptors
         isEnabledByDefault: true,
         description: "Cannot apply the [ICommand] attribute specifying to include a cancel command to methods not mapping to an asynchronous command type accepting a cancellation token.",
         helpLinkUri: "https://aka.ms/mvvmtoolkit");
+
+    /// <summary>
+    /// Gets a <see cref="DiagnosticDescriptor"/> indicating when a generated property created with <c>[ObservableProperty]</c> would collide with the source field.
+    /// <para>
+    /// Format: <c>"The field {0}.{1} cannot be used to generate an observable property, as its name would collide with the field name (instance fields should use the "lowerCamel", "_lowerCamel" or "m_lowerCamel" pattern)</c>.
+    /// </para>
+    /// </summary>
+    public static readonly DiagnosticDescriptor ObservablePropertyNameCollisionError = new DiagnosticDescriptor(
+        id: "MVVMTK0014",
+        title: "Name collision for generated property",
+        messageFormat: "The field {0}.{1} cannot be used to generate an observable property, as its name would collide with the field name (instance fields should use the \"lowerCamel\", \"_lowerCamel\" or \"m_lowerCamel\" pattern)",
+        category: typeof(ObservablePropertyGenerator).FullName,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true,
+        description: $"The name of fields annotated with [ObservableProperty] should use \"lowerCamel\", \"_lowerCamel\" or \"m_lowerCamel\" pattern to avoid collisions with the generated properties.",
+        helpLinkUri: "https://aka.ms/mvvmtoolkit");
 }

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

@@ -616,6 +616,25 @@ private async Task GreetUserAsync(User user)
         VerifyGeneratedDiagnostics<ICommandGenerator>(source, "MVVMTK0013");
     }
 
+    [TestMethod]
+    public void NameCollisionForGeneratedObservableProperty()
+    {
+        string source = @"
+            using System.ComponentModel.DataAnnotations;
+            using CommunityToolkit.Mvvm.ComponentModel;
+
+            namespace MyApp
+            {
+                public partial class SampleViewModel : ObservableObject
+                {
+                    [ObservableProperty]
+                    private string Name;
+                }
+            }";
+
+        VerifyGeneratedDiagnostics<ObservablePropertyGenerator>(source, "MVVMTK0014");
+    }
+
     /// <summary>
     /// Verifies the output of a source generator.
     /// </summary>