feat: Support CommunityToolkit.Mvvm in two way x:Bind

src/SourceGenerators/Uno.UI.SourceGenerators/XamlGenerator/XamlCodeGeneration.cs

@@ -140,6 +140,11 @@ private bool IsUnoFluentAssembly
 		internal Lazy<INamedTypeSymbol> SolidColorBrushSymbol { get; }
 		internal Lazy<INamedTypeSymbol> RowDefinitionSymbol { get; }
 		internal Lazy<INamedTypeSymbol> ColumnDefinitionSymbol { get; }
+		internal Lazy<INamedTypeSymbol> TaskSymbol { get; }
+		internal Lazy<INamedTypeSymbol?> IRelayCommandSymbol { get; }
+		internal Lazy<INamedTypeSymbol?> IRelayCommandTSymbol { get; }
+		internal Lazy<INamedTypeSymbol?> IAsyncRelayCommandSymbol { get; }
+		internal Lazy<INamedTypeSymbol?> IAsyncRelayCommandTSymbol { get; }
 
 		public XamlCodeGeneration(GeneratorExecutionContext context)
 		{
@@ -307,6 +312,11 @@ public XamlCodeGeneration(GeneratorExecutionContext context)
 			SolidColorBrushSymbol = GetMandatorySymbolAsLazy(XamlConstants.Types.SolidColorBrush);
 			RowDefinitionSymbol = GetMandatorySymbolAsLazy(XamlConstants.Types.RowDefinition);
 			ColumnDefinitionSymbol = GetMandatorySymbolAsLazy(XamlConstants.Types.ColumnDefinition);
+			TaskSymbol = GetMandatorySymbolAsLazy("System.Threading.Tasks");
+			IRelayCommandSymbol = GetOptionalSymbolAsLazy("CommunityToolkit.Mvvm.Input.IRelayCommand");
+			IRelayCommandTSymbol = GetOptionalSymbolAsLazy("CommunityToolkit.Mvvm.Input.IRelayCommand`1");
+			IAsyncRelayCommandSymbol = GetOptionalSymbolAsLazy("CommunityToolkit.Mvvm.Input.IAsyncRelayCommand");
+			IAsyncRelayCommandTSymbol = GetOptionalSymbolAsLazy("CommunityToolkit.Mvvm.Input.IAsyncRelayCommand`1");
 
 			Lazy<INamedTypeSymbol> GetMandatorySymbolAsLazy(string fullyQualifiedName)
 				=> new(() => context.Compilation.GetTypeByMetadataName(fullyQualifiedName) ?? throw new InvalidOperationException($"Unable to find type {fullyQualifiedName}"));

src/SourceGenerators/Uno.UI.SourceGenerators/XamlGenerator/XamlFileGenerator.cs

@@ -4467,19 +4467,9 @@ private ITypeSymbol GetXBindPropertyPathType(string propertyPath, INamedTypeSymb
 
 			foreach (var part in parts)
 			{
-				if (currentType.GetAllMembersWithName(part).FirstOrDefault() is ISymbol member)
+				if (TryGetPartType(currentType, part) is ITypeSymbol partType)
 				{
-					var propertySymbol = member as IPropertySymbol;
-					var fieldSymbol = member as IFieldSymbol;
-
-					if (propertySymbol != null || fieldSymbol != null)
-					{
-						currentType = propertySymbol?.Type ?? fieldSymbol?.Type!;
-					}
-					else
-					{
-						throw new InvalidOperationException($"Cannot use member [{part}] of type [{member}], as it is not a property of a field");
-					}
+					currentType = partType;
 				}
 				else if (FindSubElementByName(_fileDefinition.Objects.First(), part) is XamlObjectDefinition elementByName)
 				{
@@ -4492,11 +4482,102 @@ private ITypeSymbol GetXBindPropertyPathType(string propertyPath, INamedTypeSymb
 				}
 				else
 				{
-					throw new InvalidOperationException($"Unable to find member [{part}] on type [{currentType}]");
+					// We can't find the type. It could be something that is source-generated, or it could be a user error.
+					// For source-generated members, it's not possible to reliably get this information due to https://github.com/dotnet/roslyn/issues/57239
+					// However, we do a best effort to handle the common scenario, which is code generated by CommunityToolkit.Mvvm.
+
+					// Case 1: ObservableProperty attribute.
+					// Relevant code: https://github.com/CommunityToolkit/dotnet/blob/b341ef91fe66101444d6b811bc5dff32de029d3c/src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/ObservablePropertyGenerator.Execute.cs#L1231-L1244
+					// The user defines a field named '_abc', 'abc', 'm_abc', '_Abc', or 'm_Abc'.
+					// The generated property will be named 'Abc', which is what the user will be referencing in x:Bind.
+					ITypeSymbol? mvvmType = TryGetMvvmObservablePropertyType(currentType, part);
+
+					// Case 2: RelayCommand attribute
+					// Relevant code: https://github.com/CommunityToolkit/dotnet/blob/b341ef91fe66101444d6b811bc5dff32de029d3c/src/CommunityToolkit.Mvvm.SourceGenerators/Input/RelayCommandGenerator.Execute.cs#L455-L496
+					// and also: https://github.com/CommunityToolkit/dotnet/blob/b341ef91fe66101444d6b811bc5dff32de029d3c/src/CommunityToolkit.Mvvm.SourceGenerators/Input/RelayCommandGenerator.Execute.cs#L522-L614
+					// The user defines a method named 'OnAbcAsync', 'AbcAsync', 'OnAbc', 'Abc'.
+					// The generated command property will be named 'AbcCommand'
+					mvvmType ??= TryGetMvvmRelayCommandType(currentType, part);
+					currentType = mvvmType ?? throw new InvalidOperationException($"Unable to find member [{part}] on type [{currentType}]");
 				}
 			}
 
 			return currentType;
+
+			static ITypeSymbol? TryGetPartType(ITypeSymbol currentType, string part)
+			{
+				if (currentType.GetAllMembersWithName(part).FirstOrDefault() is ISymbol member)
+				{
+					return member switch
+					{
+						IPropertySymbol propertySymbol => propertySymbol.Type,
+						IFieldSymbol fieldSymbol => fieldSymbol.Type,
+						// We avoid throwing here in case the method is a relay command, in which case we want to get into
+						// the TryGetMvvmRelayCommandType code path.
+						IMethodSymbol methodSymbol => null,
+						_ => throw new InvalidOperationException($"Cannot use member [{part}] of type [{member}], as it is not a property of a field"),
+					};
+				}
+
+				return null;
+			}
+
+			static ITypeSymbol? TryGetMvvmObservablePropertyType(ITypeSymbol currentType, string part)
+			{
+				if (part.Length > 0 && char.IsUpper(part[0]))
+				{
+					// We could first check if the field has [ObservableAttribute], but it doesn't add enough value.
+					var firstCharLower = char.ToLower(part[0], CultureInfo.InvariantCulture);
+					var firstCharStripped = part.Substring(1);
+					var mvvmType = TryGetPartType(currentType, $"_{firstCharLower}{firstCharStripped}");
+					mvvmType ??= TryGetPartType(currentType, $"{firstCharLower}{firstCharStripped}");
+					mvvmType ??= TryGetPartType(currentType, $"m_{firstCharLower}{firstCharStripped}");
+					mvvmType ??= TryGetPartType(currentType, $"_{part}");
+					mvvmType ??= TryGetPartType(currentType, $"m_{part}");
+					return mvvmType;
+				}
+
+				return null;
+			}
+
+			ITypeSymbol? TryGetMvvmRelayCommandType(ITypeSymbol currentType, string part)
+			{
+				const string CommandSuffix = "Command";
+				if (part.EndsWith(CommandSuffix, StringComparison.Ordinal))
+				{
+					// We could first check if the method has [RelayCommand], but it doesn't add enough value.
+					part = part.Substring(0, part.Length - CommandSuffix.Length);
+					var method = currentType.GetAllMembersWithName(part).FirstOrDefault() as IMethodSymbol;
+					method ??= currentType.GetAllMembersWithName($"On{part}").FirstOrDefault() as IMethodSymbol;
+					method ??= currentType.GetAllMembersWithName($"On{part}Async").FirstOrDefault() as IMethodSymbol;
+					method ??= currentType.GetAllMembersWithName($"{part}Async").FirstOrDefault() as IMethodSymbol;
+
+					if (method is not null)
+					{
+						if (method.ReturnsVoid && method.Parameters.Length == 0)
+						{
+							return Generation.IRelayCommandSymbol.Value;
+						}
+						else if (method.ReturnsVoid && method.Parameters.Length == 1)
+						{
+							return Generation.IRelayCommandTSymbol.Value?.Construct(method.Parameters[0].Type);
+						}
+						else if (method.ReturnType is INamedTypeSymbol namedType && namedType.Is(Generation.TaskSymbol.Value))
+						{
+							if (method.Parameters.Length == 0)
+							{
+								return Generation.IAsyncRelayCommandSymbol.Value;
+							}
+							else if (method.Parameters.Length is 1 or 2)
+							{
+								return Generation.IAsyncRelayCommandTSymbol.Value?.Construct(method.Parameters[0].Type);
+							}
+						}
+					}
+				}
+
+				return null;
+			}
 		}
 
 		private bool IsStaticMember(string fullMemberName)