Merge pull request #475 from CommunityToolkit/dev/lower-command-names

Fix [RelayCommand] for methods that can't be lowered

Author: Sergio0694

CommunityToolkit.Mvvm.SourceGenerators/Input/RelayCommandGenerator.Execute.cs

@@ -439,7 +439,17 @@ public static (string FieldName, string PropertyName) GetGeneratedFieldAndProper
 
             propertyName += "Command";
 
-            string fieldName = $"{char.ToLower(propertyName[0], CultureInfo.InvariantCulture)}{propertyName.Substring(1)}";
+            char firstCharacter = propertyName[0];
+            char loweredFirstCharacter = char.ToLower(firstCharacter, CultureInfo.InvariantCulture);
+
+            // The field name is generated depending on whether the first character can be lowered:
+            //   - If it can, then the field name is just the property name starting in lowercase.
+            //   - If it can't (eg. starts with '中'), then the '_' prefix is added to the property name.
+            string fieldName = (firstCharacter == loweredFirstCharacter) switch
+            {
+                true => $"_{propertyName}",
+                false => $"{loweredFirstCharacter}{propertyName.Substring(1)}"
+            };
 
             return (fieldName, propertyName);
         }

tests/CommunityToolkit.Mvvm.UnitTests/Test_ObservablePropertyAttribute.cs

@@ -946,6 +946,25 @@ public void Test_ObservableProperty_WithExplicitAttributeForProperty()
         Assert.AreEqual(testAttribute2.Animal, (Animal)67);
     }
 
+    // See https://github.com/CommunityToolkit/dotnet/issues/446
+    [TestMethod]
+    public void Test_ObservableProperty_CommandNamesThatCantBeLowered()
+    {
+        ModelWithCommandNamesThatCantBeLowered model = new();
+
+        // Just ensures this builds
+        _ = model.中文Command;
+        _ = model.c中文Command;
+
+        FieldInfo? fieldInfo = typeof(ModelWithCommandNamesThatCantBeLowered).GetField($"_{nameof(ModelWithCommandNamesThatCantBeLowered.中文)}Command", BindingFlags.Instance | BindingFlags.NonPublic);
+
+        Assert.AreSame(model.中文Command, fieldInfo.GetValue(model));
+
+        fieldInfo = typeof(ModelWithCommandNamesThatCantBeLowered).GetField($"_{nameof(ModelWithCommandNamesThatCantBeLowered.c中文)}Command", BindingFlags.Instance | BindingFlags.NonPublic);
+
+        Assert.AreSame(model.c中文Command, fieldInfo.GetValue(model));
+    }
+
     public abstract partial class BaseViewModel : ObservableObject
     {
         public string? Content { get; set; }
@@ -1517,4 +1536,17 @@ public PropertyInfoAttribute(object? o, Type t, bool flag, double d, string[] na
 
         public Animal Animal { get; set; }
     }
+
+    private sealed partial class ModelWithCommandNamesThatCantBeLowered
+    {
+        [RelayCommand]
+        public void 中文()
+        {
+        }
+
+        [RelayCommand]
+        public void c中文()
+        {
+        }
+    }
 }