ObservablePropertyGenerator.Execute.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Collections.Immutable;
using System.ComponentModel;
using System.Linq;
using CommunityToolkit.Mvvm.SourceGenerators.ComponentModel.Models;
using CommunityToolkit.Mvvm.SourceGenerators.Diagnostics;
using CommunityToolkit.Mvvm.SourceGenerators.Extensions;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using static CommunityToolkit.Mvvm.SourceGenerators.Diagnostics.DiagnosticDescriptors;
using static Microsoft.CodeAnalysis.CSharp.SyntaxFactory;

namespace CommunityToolkit.Mvvm.SourceGenerators;

/// <inheritdoc/>
partial class ObservablePropertyGenerator
{
    /// <summary>
    /// A container for all the logic for <see cref="ObservablePropertyGenerator"/>.
    /// </summary>
    internal static class Execute
    {
        /// <summary>
        /// Processes a given field.
        /// </summary>
        /// <param name="fieldSymbol">The input <see cref="IFieldSymbol"/> instance to process.</param>
        /// <param name="diagnostics">The resulting diagnostics from the processing operation.</param>
        /// <returns>The resulting <see cref="PropertyInfo"/> instance for <paramref name="fieldSymbol"/>, if successful.</returns>
        public static PropertyInfo? TryGetInfo(IFieldSymbol fieldSymbol, out ImmutableArray<Diagnostic> diagnostics)
        {
            ImmutableArray<Diagnostic>.Builder builder = ImmutableArray.CreateBuilder<Diagnostic>();

            // Validate the target type
            if (!IsTargetTypeValid(fieldSymbol, out bool shouldInvokeOnPropertyChanging))
            {
                builder.Add(
                    InvalidContainingTypeForObservablePropertyFieldError,
                    fieldSymbol,
                    fieldSymbol.ContainingType,
                    fieldSymbol.Name);

                diagnostics = builder.ToImmutable();

                return null;
            }

            // Get the property type and name
            string typeNameWithNullabilityAnnotations = fieldSymbol.Type.GetFullyQualifiedNameWithNullabilityAnnotations();
            string fieldName = fieldSymbol.Name;
            string propertyName = GetGeneratedPropertyName(fieldSymbol);

            // Check for name collisions
            if (fieldName == propertyName)
            {
                builder.Add(
                    ObservablePropertyNameCollisionError,
                    fieldSymbol,
                    fieldSymbol.ContainingType,
                    fieldSymbol.Name);

                diagnostics = builder.ToImmutable();

                // If the generated property would collide, skip generating it entirely. This makes sure that
                // users only get the helpful diagnostic about the collision, and not the normal compiler error
                // about a definition for "Property" already existing on the target type, which might be confusing.
                return null;
            }

            ImmutableArray<string>.Builder propertyChangedNames = ImmutableArray.CreateBuilder<string>();
            ImmutableArray<string>.Builder propertyChangingNames = ImmutableArray.CreateBuilder<string>();
            ImmutableArray<string>.Builder notifiedCommandNames = ImmutableArray.CreateBuilder<string>();
            ImmutableArray<AttributeInfo>.Builder validationAttributes = ImmutableArray.CreateBuilder<AttributeInfo>();
            bool alsoBroadcastChange = false;

            // Track the property changing event for the property, if the type supports it
            if (shouldInvokeOnPropertyChanging)
            {
                propertyChangingNames.Add(propertyName);
            }

            // The current property is always notified
            propertyChangedNames.Add(propertyName);

            // Gather attributes info
            foreach (AttributeData attributeData in fieldSymbol.GetAttributes())
            {
                // Gather dependent property and command names
                if (TryGatherDependentPropertyChangedNames(fieldSymbol, attributeData, propertyChangedNames, builder) ||
                    TryGatherDependentCommandNames(fieldSymbol, attributeData, notifiedCommandNames, builder) ||
                    TryGetIsBroadcastingChanges(fieldSymbol, attributeData, builder, out alsoBroadcastChange))
                {
                    continue;
                }

                // Track the current validation attribute, if applicable
                if (attributeData.AttributeClass?.InheritsFromFullyQualifiedName("global::System.ComponentModel.DataAnnotations.ValidationAttribute") == true)
                {
                    validationAttributes.Add(AttributeInfo.From(attributeData));
                }
            }

            // Log the diagnostics if needed
            if (validationAttributes.Count > 0 &&
                !fieldSymbol.ContainingType.InheritsFromFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.ObservableValidator"))
            {
                builder.Add(
                    MissingObservableValidatorInheritanceError,
                    fieldSymbol,
                    fieldSymbol.ContainingType,
                    fieldSymbol.Name,
                    validationAttributes.Count);

                // Remove all validation attributes so that the generated code doesn't cause a build error about the
                // "ValidateProperty" method not existing (as the type doesn't inherit from ObservableValidator). The
                // compilation will still fail due to this diagnostics, but with just this easier to understand error.
                validationAttributes.Clear();
            }

            diagnostics = builder.ToImmutable();

            return new(
                typeNameWithNullabilityAnnotations,
                fieldName,
                propertyName,
                propertyChangingNames.ToImmutable(),
                propertyChangedNames.ToImmutable(),
                notifiedCommandNames.ToImmutable(),
                alsoBroadcastChange,
                validationAttributes.ToImmutable());
        }

        /// <summary>
        /// Gets the diagnostics for a field with invalid attribute uses.
        /// </summary>
        /// <param name="fieldSymbol">The input <see cref="IFieldSymbol"/> instance to process.</param>
        /// <returns>The resulting <see cref="Diagnostic"/> instance for <paramref name="fieldSymbol"/>.</returns>
        public static Diagnostic GetDiagnosticForFieldWithOrphanedDependentAttributes(IFieldSymbol fieldSymbol)
        {
            return FieldWithOrphanedDependentObservablePropertyAttributesError.CreateDiagnostic(
                fieldSymbol,
                fieldSymbol.ContainingType,
                fieldSymbol.Name);
        }

        /// <summary>
        /// Validates the containing type for a given field being annotated.
        /// </summary>
        /// <param name="fieldSymbol">The input <see cref="IFieldSymbol"/> instance to process.</param>
        /// <param name="shouldInvokeOnPropertyChanging">Whether or not property changing events should also be raised.</param>
        /// <returns>Whether or not the containing type for <paramref name="fieldSymbol"/> is valid.</returns>
        private static bool IsTargetTypeValid(
            IFieldSymbol fieldSymbol,
            out bool shouldInvokeOnPropertyChanging)
        {
            // The [ObservableProperty] attribute can only be used in types that are known to expose the necessary OnPropertyChanged and OnPropertyChanging methods.
            // That means that the containing type for the field needs to match one of the following conditions:
            //   - It inherits from ObservableObject (in which case it also implements INotifyPropertyChanging).
            //   - It has the [ObservableObject] attribute (on itself or any of its base types).
            //   - It has the [INotifyPropertyChanged] attribute (on itself or any of its base types).
            bool isObservableObject = fieldSymbol.ContainingType.InheritsFromFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.ObservableObject");
            bool hasObservableObjectAttribute = fieldSymbol.ContainingType.HasOrInheritsAttributeWithFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.ObservableObjectAttribute");
            bool hasINotifyPropertyChangedAttribute = fieldSymbol.ContainingType.HasOrInheritsAttributeWithFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.INotifyPropertyChangedAttribute");

            shouldInvokeOnPropertyChanging = isObservableObject || hasObservableObjectAttribute;

            return isObservableObject || hasObservableObjectAttribute || hasINotifyPropertyChangedAttribute;
        }

        /// <summary>
        /// Tries to gather dependent properties from the given attribute.
        /// </summary>
        /// <param name="fieldSymbol">The input <see cref="IFieldSymbol"/> instance to process.</param>
        /// <param name="attributeData">The <see cref="AttributeData"/> instance for <paramref name="fieldSymbol"/>.</param>
        /// <param name="propertyChangedNames">The target collection of dependent property names to populate.</param>
        /// <param name="diagnostics">The current collection of gathered diagnostics.</param>
        /// <returns>Whether or not <paramref name="attributeData"/> was an attribute containing any dependent properties.</returns>
        private static bool TryGatherDependentPropertyChangedNames(
            IFieldSymbol fieldSymbol,
            AttributeData attributeData,
            ImmutableArray<string>.Builder propertyChangedNames,
            ImmutableArray<Diagnostic>.Builder diagnostics)
        {
            // Validates a property name using existing properties
            bool IsPropertyNameValid(string propertyName)
            {
                return fieldSymbol.ContainingType.GetAllMembers(propertyName).OfType<IPropertySymbol>().Any();
            }

            // Validate a property name including generated properties too
            bool IsPropertyNameValidWithGeneratedMembers(string propertyName)
            {
                foreach (ISymbol member in fieldSymbol.ContainingType.GetAllMembers())
                {
                    if (member is IFieldSymbol otherFieldSymbol &&
                        !SymbolEqualityComparer.Default.Equals(fieldSymbol, otherFieldSymbol) &&
                        otherFieldSymbol.HasAttributeWithFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.ObservablePropertyAttribute") &&
                        propertyName == GetGeneratedPropertyName(otherFieldSymbol))
                    {
                        return true;
                    }
                }

                return false;
            }

            if (attributeData.AttributeClass?.HasFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.AlsoNotifyChangeForAttribute") == true)
            {
                foreach (string? dependentPropertyName in attributeData.GetConstructorArguments<string>())
                {
                    // Each target must be a (not null and not empty) string matching the name of a property from the containing type
                    // of the annotated field being processed, or alternatively it must match the name of a property being generated.
                    if (dependentPropertyName is not (null or "") &&
                        (IsPropertyNameValid(dependentPropertyName) ||
                         IsPropertyNameValidWithGeneratedMembers(dependentPropertyName)))
                    {
                        propertyChangedNames.Add(dependentPropertyName);
                    }
                    else
                    {
                        diagnostics.Add(
                            AlsoNotifyChangeForInvalidTargetError,
                            fieldSymbol,
                            dependentPropertyName ?? "",
                            fieldSymbol.ContainingType);
                    }
                }

                return true;
            }

            return false;
        }

        /// <summary>
        /// Tries to gather dependent commands from the given attribute.
        /// </summary>
        /// <param name="fieldSymbol">The input <see cref="IFieldSymbol"/> instance to process.</param>
        /// <param name="attributeData">The <see cref="AttributeData"/> instance for <paramref name="fieldSymbol"/>.</param>
        /// <param name="notifiedCommandNames">The target collection of dependent command names to populate.</param>
        /// <param name="diagnostics">The current collection of gathered diagnostics.</param>
        /// <returns>Whether or not <paramref name="attributeData"/> was an attribute containing any dependent commands.</returns>
        private static bool TryGatherDependentCommandNames(
            IFieldSymbol fieldSymbol,
            AttributeData attributeData,
            ImmutableArray<string>.Builder notifiedCommandNames,
            ImmutableArray<Diagnostic>.Builder diagnostics)
        {
            // Validates a command name using existing properties
            bool IsCommandNameValid(string commandName, out bool shouldLookForGeneratedMembersToo)
            {
                // Each target must be a string matching the name of a property from the containing type of the annotated field, and the
                // property must be of type IRelayCommand, or any type that implements that interface (to avoid generating invalid code).
                if (fieldSymbol.ContainingType.GetAllMembers(commandName).OfType<IPropertySymbol>().FirstOrDefault() is IPropertySymbol propertySymbol)
                {
                    // If there is a property member with the specified name, check that it's valid. If it isn't, the
                    // target is definitely not valid, and the additional checks below can just be skipped. The property
                    // is valid if it's of type IRelayCommand, or it has IRelayCommand in the set of all interfaces.
                    if (propertySymbol.Type is INamedTypeSymbol typeSymbol &&
                        (typeSymbol.HasFullyQualifiedName("global::CommunityToolkit.Mvvm.Input.IRelayCommand") ||
                         typeSymbol.HasInterfaceWithFullyQualifiedName("global::CommunityToolkit.Mvvm.Input.IRelayCommand")))
                    {
                        shouldLookForGeneratedMembersToo = true;

                        return true;
                    }

                    // If a property with this name exists but is not valid, the search should stop immediately, as
                    // the target is already known not to be valid, so there is no reason to look for other members.
                    shouldLookForGeneratedMembersToo = false;

                    return false;
                }

                shouldLookForGeneratedMembersToo = true;

                return false;
            }

            // Validate a command name including generated command too
            bool IsCommandNameValidWithGeneratedMembers(string commandName)
            {
                foreach (ISymbol member in fieldSymbol.ContainingType.GetAllMembers())
                {
                    if (member is IMethodSymbol methodSymbol &&
                        methodSymbol.HasAttributeWithFullyQualifiedName("global::CommunityToolkit.Mvvm.Input.ICommandAttribute") &&
                        commandName == ICommandGenerator.Execute.GetGeneratedFieldAndPropertyNames(methodSymbol).PropertyName)
                    {
                        return true;
                    }
                }

                return false;
            }

            if (attributeData.AttributeClass?.HasFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.AlsoNotifyCanExecuteForAttribute") == true)
            {
                foreach (string? commandName in attributeData.GetConstructorArguments<string>())
                {
                    // Each command must be a (not null and not empty) string matching the name of an existing command from the containing
                    // type (just like for properties), or it must match a generated command. The only caveat is the case where a property
                    // with the requested name does exist, but it is not of the right type. In that case the search should stop immediately.
                    if (commandName is not (null or "") &&
                        (IsCommandNameValid(commandName, out bool shouldLookForGeneratedMembersToo) ||
                         shouldLookForGeneratedMembersToo && IsCommandNameValidWithGeneratedMembers(commandName)))
                    {
                        notifiedCommandNames.Add(commandName);
                    }
                    else
                    {
                        diagnostics.Add(
                           AlsoNotifyCanExecuteForInvalidTargetError,
                           fieldSymbol,
                           commandName ?? "",
                           fieldSymbol.ContainingType);
                    }
                }

                return true;
            }

            return false;
        }

        /// <summary>
        /// Checks whether a given generated property should also broadcast changes.
        /// </summary>
        /// <param name="fieldSymbol">The input <see cref="IFieldSymbol"/> instance to process.</param>
        /// <param name="attributeData">The <see cref="AttributeData"/> instance for <paramref name="fieldSymbol"/>.</param>
        /// <param name="diagnostics">The current collection of gathered diagnostics.</param>
        /// <param name="alsoBroadcastChange">Whether or not the resulting property should also broadcast changes.</param>
        /// <returns>Whether or not the generated property for <paramref name="fieldSymbol"/> used <c>[AlsoBroadcastChange]</c>.</returns>
        private static bool TryGetIsBroadcastingChanges(
            IFieldSymbol fieldSymbol,
            AttributeData attributeData,
            ImmutableArray<Diagnostic>.Builder diagnostics,
            out bool alsoBroadcastChange)
        {
            if (attributeData.AttributeClass?.HasFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.AlsoBroadcastChangeAttribute") == true)
            {
                // If the containing type is valid, track it
                if (fieldSymbol.ContainingType.InheritsFromFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.ObservableRecipient") ||
                    fieldSymbol.ContainingType.HasOrInheritsAttributeWithFullyQualifiedName("global::CommunityToolkit.Mvvm.ComponentModel.ObservableRecipientAttribute"))
                {
                    alsoBroadcastChange = true;

                    return true;
                }

                // Otherwise just emit the diagnostic and then ignore the attribute
                diagnostics.Add(
                    InvalidContainingTypeForAlsoBroadcastChangeFieldError,
                    fieldSymbol,
                    fieldSymbol.ContainingType,
                    fieldSymbol.Name);

                alsoBroadcastChange = false;

                return true;
            }

            alsoBroadcastChange = false;

            return false;
        }

        /// <summary>
        /// Gets a <see cref="CompilationUnitSyntax"/> instance with the cached args for property changing notifications.
        /// </summary>
        /// <param name="names">The sequence of property names to cache args for.</param>
        /// <returns>A <see cref="CompilationUnitSyntax"/> instance with the sequence of cached args, if any.</returns>
        public static CompilationUnitSyntax? GetKnownPropertyChangingArgsSyntax(ImmutableArray<string> names)
        {
            return GetKnownPropertyChangingOrChangedArgsSyntax(
                "__KnownINotifyPropertyChangingArgs",
                "global::System.ComponentModel.PropertyChangingEventArgs",
                names);
        }

        /// <summary>
        /// Gets a <see cref="CompilationUnitSyntax"/> instance with the cached args for property changed notifications.
        /// </summary>
        /// <param name="names">The sequence of property names to cache args for.</param>
        /// <returns>A <see cref="CompilationUnitSyntax"/> instance with the sequence of cached args, if any.</returns>
        public static CompilationUnitSyntax? GetKnownPropertyChangedArgsSyntax(ImmutableArray<string> names)
        {
            return GetKnownPropertyChangingOrChangedArgsSyntax(
                "__KnownINotifyPropertyChangedArgs",
                "global::System.ComponentModel.PropertyChangedEventArgs",
                names);
        }

        /// <summary>
        /// Gets the <see cref="MemberDeclarationSyntax"/> instance for the input field.
        /// </summary>
        /// <param name="propertyInfo">The input <see cref="PropertyInfo"/> instance to process.</param>
        /// <returns>The generated <see cref="MemberDeclarationSyntax"/> instance for <paramref name="propertyInfo"/>.</returns>
        public static MemberDeclarationSyntax GetPropertySyntax(PropertyInfo propertyInfo)
        {
            ImmutableArray<StatementSyntax>.Builder setterStatements = ImmutableArray.CreateBuilder<StatementSyntax>();

            // Get the property type syntax
            TypeSyntax propertyType = IdentifierName(propertyInfo.TypeNameWithNullabilityAnnotations);

            // In case the backing field is exactly named "value", we need to add the "this." prefix to ensure that comparisons and assignments
            // with it in the generated setter body are executed correctly and without conflicts with the implicit value parameter.
            ExpressionSyntax fieldExpression = propertyInfo.FieldName switch
            {
                "value" => MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression, ThisExpression(), IdentifierName("value")),
                string name => IdentifierName(name)
            };

            if (propertyInfo.AlsoBroadcastChange)
            {
                // If broadcasting changes are required, also store the old value.
                // This code generates a statement as follows:
                //
                // <PROPERTY_TYPE> __oldValue = <FIELD_EXPRESSIONS>;
                setterStatements.Add(
                    LocalDeclarationStatement(
                        VariableDeclaration(propertyType)
                        .AddVariables(
                            VariableDeclarator(Identifier("__oldValue"))
                            .WithInitializer(EqualsValueClause(fieldExpression)))));
            }

            // Add the OnPropertyChanging() call first:
            //
            // On<PROPERTY_NAME>Changing(value);
            setterStatements.Add(
                ExpressionStatement(
                    InvocationExpression(IdentifierName($"On{propertyInfo.PropertyName}Changing"))
                    .AddArgumentListArguments(Argument(IdentifierName("value")))));

            // Gather the statements to notify dependent properties
            foreach (string propertyName in propertyInfo.PropertyChangingNames)
            {
                // This code generates a statement as follows:
                //
                // OnPropertyChanging(global::CommunityToolkit.Mvvm.ComponentModel.__Internals.__KnownINotifyPropertyChangingArgs.<PROPERTY_NAME>);
                setterStatements.Add(
                    ExpressionStatement(
                        InvocationExpression(IdentifierName("OnPropertyChanging"))
                        .AddArgumentListArguments(Argument(MemberAccessExpression(
                            SyntaxKind.SimpleMemberAccessExpression,
                            IdentifierName("global::CommunityToolkit.Mvvm.ComponentModel.__Internals.__KnownINotifyPropertyChangingArgs"),
                            IdentifierName(propertyName))))));
            }

            // Add the assignment statement:
            //
            // <FIELD_EXPRESSION> = value;
            setterStatements.Add(
                ExpressionStatement(
                    AssignmentExpression(
                        SyntaxKind.SimpleAssignmentExpression,
                        fieldExpression,
                        IdentifierName("value"))));

            // If there are validation attributes, add a call to ValidateProperty:
            //
            // ValidateProperty(value, <PROPERTY_NAME>);
            if (propertyInfo.ValidationAttributes.Length > 0)
            {
                setterStatements.Add(
                    ExpressionStatement(
                        InvocationExpression(IdentifierName("ValidateProperty"))
                        .AddArgumentListArguments(
                            Argument(IdentifierName("value")),
                            Argument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(propertyInfo.PropertyName))))));
            }

            // Add the OnPropertyChanged() call:
            //
            // On<PROPERTY_NAME>Changed(value);
            setterStatements.Add(
                ExpressionStatement(
                    InvocationExpression(IdentifierName($"On{propertyInfo.PropertyName}Changed"))
                    .AddArgumentListArguments(Argument(IdentifierName("value")))));

            // Gather the statements to notify dependent properties
            foreach (string propertyName in propertyInfo.PropertyChangedNames)
            {
                // This code generates a statement as follows:
                //
                // OnPropertyChanging(global::CommunityToolkit.Mvvm.ComponentModel.__Internals.__KnownINotifyPropertyChangedArgs.<PROPERTY_NAME>);
                setterStatements.Add(
                    ExpressionStatement(
                        InvocationExpression(IdentifierName("OnPropertyChanged"))
                        .AddArgumentListArguments(Argument(MemberAccessExpression(
                            SyntaxKind.SimpleMemberAccessExpression,
                            IdentifierName("global::CommunityToolkit.Mvvm.ComponentModel.__Internals.__KnownINotifyPropertyChangedArgs"),
                            IdentifierName(propertyName))))));
            }

            // Gather the statements to notify commands
            foreach (string commandName in propertyInfo.NotifiedCommandNames)
            {
                // This code generates a statement as follows:
                //
                // <COMMAND_NAME>.NotifyCanExecuteChanged();
                setterStatements.Add(
                    ExpressionStatement(
                        InvocationExpression(MemberAccessExpression(
                            SyntaxKind.SimpleMemberAccessExpression,
                            IdentifierName(commandName),
                            IdentifierName("NotifyCanExecuteChanged")))));
            }

            // Also broadcast the change, if requested
            if (propertyInfo.AlsoBroadcastChange)
            {
                // This code generates a statement as follows:
                //
                // Broadcast(__oldValue, value, "<PROPERTY_NAME>");
                setterStatements.Add(
                    ExpressionStatement(
                        InvocationExpression(IdentifierName("Broadcast"))
                        .AddArgumentListArguments(
                            Argument(IdentifierName("__oldValue")),
                            Argument(IdentifierName("value")),
                            Argument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(propertyInfo.PropertyName))))));
            }

            // Generate the inner setter block as follows:
            //
            // if (!global::System.Collections.Generic.EqualityComparer<<PROPERTY_TYPE>>.Default.Equals(<FIELD_EXPRESSION>, value))
            // {
            //     <STATEMENTS>
            // }
            IfStatementSyntax setterIfStatement =
                IfStatement(
                    PrefixUnaryExpression(
                        SyntaxKind.LogicalNotExpression,
                        InvocationExpression(
                            MemberAccessExpression(
                                SyntaxKind.SimpleMemberAccessExpression,
                                MemberAccessExpression(
                                    SyntaxKind.SimpleMemberAccessExpression,
                                    GenericName(Identifier("global::System.Collections.Generic.EqualityComparer"))
                                    .AddTypeArgumentListArguments(propertyType),
                                    IdentifierName("Default")),
                                IdentifierName("Equals")))
                        .AddArgumentListArguments(
                            Argument(fieldExpression),
                            Argument(IdentifierName("value")))),
                    Block(setterStatements));

            // Prepare the validation attributes, if any
            ImmutableArray<AttributeListSyntax> validationAttributes =
                propertyInfo.ValidationAttributes
                .Select(static a => AttributeList(SingletonSeparatedList(a.GetSyntax())))
                .ToImmutableArray();

            // Construct the generated property as follows:
            //
            // /// <inheritdoc cref="<FIELD_NAME>"/>
            // [global::System.CodeDom.Compiler.GeneratedCode("...", "...")]
            // [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
            // <VALIDATION_ATTRIBUTES>
            // public <FIELD_TYPE><NULLABLE_ANNOTATION?> <PROPERTY_NAME>
            // {
            //     get => <FIELD_NAME>;
            //     set
            //     {
            //         <BODY>
            //     }
            // }
            return
                PropertyDeclaration(propertyType, Identifier(propertyInfo.PropertyName))
                .AddAttributeLists(
                    AttributeList(SingletonSeparatedList(
                        Attribute(IdentifierName("global::System.CodeDom.Compiler.GeneratedCode"))
                        .AddArgumentListArguments(
                            AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(ObservablePropertyGenerator).FullName))),
                            AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(ObservablePropertyGenerator).Assembly.GetName().Version.ToString()))))))
                    .WithOpenBracketToken(Token(TriviaList(Comment($"/// <inheritdoc cref=\"{propertyInfo.FieldName}\"/>")), SyntaxKind.OpenBracketToken, TriviaList())),
                    AttributeList(SingletonSeparatedList(Attribute(IdentifierName("global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage")))))
                .AddAttributeLists(validationAttributes.ToArray())
                .AddModifiers(Token(SyntaxKind.PublicKeyword))
                .AddAccessorListAccessors(
                    AccessorDeclaration(SyntaxKind.GetAccessorDeclaration)
                    .WithExpressionBody(ArrowExpressionClause(IdentifierName(propertyInfo.FieldName)))
                    .WithSemicolonToken(Token(SyntaxKind.SemicolonToken)),
                    AccessorDeclaration(SyntaxKind.SetAccessorDeclaration)
                    .WithBody(Block(setterIfStatement)));
        }

        /// <summary>
        /// Gets the <see cref="MemberDeclarationSyntax"/> instances for the <c>OnPropertyChanging</c> and <c>OnPropertyChanged</c> methods for the input field.
        /// </summary>
        /// <param name="propertyInfo">The input <see cref="PropertyInfo"/> instance to process.</param>
        /// <returns>The generated <see cref="MemberDeclarationSyntax"/> instances for the <c>OnPropertyChanging</c> and <c>OnPropertyChanged</c> methods.</returns>
        public static ImmutableArray<MemberDeclarationSyntax> GetOnPropertyChangeMethodsSyntax(PropertyInfo propertyInfo)
        {
            // Get the property type syntax
            TypeSyntax parameterType = IdentifierName(propertyInfo.TypeNameWithNullabilityAnnotations);

            // Construct the generated method as follows:
            //
            // /// <summary>Executes the logic for when <see cref="<PROPERTY_NAME>"/> is changing.</summary>
            // [global::System.CodeDom.Compiler.GeneratedCode("...", "...")]
            // partial void On<PROPERTY_NAME>Changing(<PROPERTY_TYPE> value);
            MemberDeclarationSyntax onPropertyChangingDeclaration =
                MethodDeclaration(PredefinedType(Token(SyntaxKind.VoidKeyword)), Identifier($"On{propertyInfo.PropertyName}Changing"))
                .AddModifiers(Token(SyntaxKind.PartialKeyword))
                .AddParameterListParameters(Parameter(Identifier("value")).WithType(parameterType))
                .AddAttributeLists(
                    AttributeList(SingletonSeparatedList(
                        Attribute(IdentifierName("global::System.CodeDom.Compiler.GeneratedCode"))
                        .AddArgumentListArguments(
                            AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(ObservablePropertyGenerator).FullName))),
                            AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(ObservablePropertyGenerator).Assembly.GetName().Version.ToString()))))))
                    .WithOpenBracketToken(Token(TriviaList(Comment($"/// <summary>Executes the logic for when <see cref=\"{propertyInfo.PropertyName}\"/> is changing.</summary>")), SyntaxKind.OpenBracketToken, TriviaList())))
                .WithSemicolonToken(Token(SyntaxKind.SemicolonToken));

            // Construct the generated method as follows:
            //
            // /// <summary>Executes the logic for when <see cref="<PROPERTY_NAME>"/> ust changed.</summary>
            // [global::System.CodeDom.Compiler.GeneratedCode("...", "...")]
            // partial void On<PROPERTY_NAME>Changed(<PROPERTY_TYPE> value);
            MemberDeclarationSyntax onPropertyChangedDeclaration =
                MethodDeclaration(PredefinedType(Token(SyntaxKind.VoidKeyword)), Identifier($"On{propertyInfo.PropertyName}Changed"))
                .AddModifiers(Token(SyntaxKind.PartialKeyword))
                .AddParameterListParameters(Parameter(Identifier("value")).WithType(parameterType))
                .AddAttributeLists(
                    AttributeList(SingletonSeparatedList(
                        Attribute(IdentifierName("global::System.CodeDom.Compiler.GeneratedCode"))
                        .AddArgumentListArguments(
                            AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(ObservablePropertyGenerator).FullName))),
                            AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(ObservablePropertyGenerator).Assembly.GetName().Version.ToString()))))))
                    .WithOpenBracketToken(Token(TriviaList(Comment($"/// <summary>Executes the logic for when <see cref=\"{propertyInfo.PropertyName}\"/> just changed.</summary>")), SyntaxKind.OpenBracketToken, TriviaList())))
                .WithSemicolonToken(Token(SyntaxKind.SemicolonToken));

            return ImmutableArray.Create(onPropertyChangingDeclaration, onPropertyChangedDeclaration);
        }

        /// <summary>
        /// Gets a <see cref="CompilationUnitSyntax"/> instance with the cached args of a specified type.
        /// </summary>
        /// <param name="ContainingTypeName">The name of the generated type.</param>
        /// <param name="ArgsTypeName">The argument type name.</param>
        /// <param name="names">The sequence of property names to cache args for.</param>
        /// <returns>A <see cref="CompilationUnitSyntax"/> instance with the sequence of cached args, if any.</returns>
        private static CompilationUnitSyntax? GetKnownPropertyChangingOrChangedArgsSyntax(
            string ContainingTypeName,
            string ArgsTypeName,
            ImmutableArray<string> names)
        {
            if (names.IsEmpty)
            {
                return null;
            }

            // This code takes a class symbol and produces a compilation unit as follows:
            //
            // // <auto-generated/>
            // #pragma warning disable
            // #nullable enable
            // namespace CommunityToolkit.Mvvm.ComponentModel.__Internals
            // {
            //     [global::System.CodeDom.Compiler.GeneratedCode("...", "...")]
            //     [global::System.Diagnostics.DebuggerNonUserCode]
            //     [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
            //     [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
            //     [global::System.Obsolete("This type is not intended to be used directly by user code")]
            //     internal static class <CONTAINING_TYPE_NAME>
            //     {
            //         <FIELDS>
            //     }
            // }
            return
                CompilationUnit().AddMembers(
                NamespaceDeclaration(IdentifierName("CommunityToolkit.Mvvm.ComponentModel.__Internals")).WithLeadingTrivia(TriviaList(
                    Comment("// <auto-generated/>"),
                    Trivia(PragmaWarningDirectiveTrivia(Token(SyntaxKind.DisableKeyword), true)),
                    Trivia(NullableDirectiveTrivia(Token(SyntaxKind.EnableKeyword), true)))).AddMembers(
                ClassDeclaration(ContainingTypeName).AddModifiers(
                    Token(SyntaxKind.InternalKeyword),
                    Token(SyntaxKind.StaticKeyword)).AddAttributeLists(
                        AttributeList(SingletonSeparatedList(
                            Attribute(IdentifierName($"global::System.CodeDom.Compiler.GeneratedCode"))
                            .AddArgumentListArguments(
                                AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(ObservablePropertyGenerator).FullName))),
                                AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(ObservablePropertyGenerator).Assembly.GetName().Version.ToString())))))),
                        AttributeList(SingletonSeparatedList(Attribute(IdentifierName("global::System.Diagnostics.DebuggerNonUserCode")))),
                        AttributeList(SingletonSeparatedList(Attribute(IdentifierName("global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage")))),
                        AttributeList(SingletonSeparatedList(
                            Attribute(IdentifierName("global::System.ComponentModel.EditorBrowsable")).AddArgumentListArguments(
                            AttributeArgument(ParseExpression("global::System.ComponentModel.EditorBrowsableState.Never"))))),
                        AttributeList(SingletonSeparatedList(
                            Attribute(IdentifierName("global::System.Obsolete")).AddArgumentListArguments(
                            AttributeArgument(LiteralExpression(
                                SyntaxKind.StringLiteralExpression,
                                Literal("This type is not intended to be used directly by user code")))))))
                    .AddMembers(names.Select(name => CreateFieldDeclaration(ArgsTypeName, name)).ToArray())))
                .NormalizeWhitespace();
        }

        /// <summary>
        /// Creates a field declaration for a cached property changing/changed name.
        /// </summary>
        /// <param name="typeName">The field type name (either <see cref="PropertyChangedEventArgs"/> or <see cref="PropertyChangingEventArgs"/>).</param>
        /// <param name="propertyName">The name of the cached property name.</param>
        /// <returns>A <see cref="FieldDeclarationSyntax"/> instance for the input cached property name.</returns>
        private static FieldDeclarationSyntax CreateFieldDeclaration(string typeName, string propertyName)
        {
            // Create a static field with a cached property changed/changing argument for a specified property.
            // This code produces a field declaration as follows:
            //
            // [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
            // [global::System.Obsolete("This field is not intended to be referenced directly by user code")]
            // public static readonly <ARG_TYPE> <PROPERTY_NAME> = new("<PROPERTY_NAME>");
            return
                FieldDeclaration(
                VariableDeclaration(IdentifierName(typeName))
                .AddVariables(
                    VariableDeclarator(Identifier(propertyName))
                    .WithInitializer(EqualsValueClause(
                        ImplicitObjectCreationExpression()
                        .AddArgumentListArguments(Argument(
                            LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(propertyName))))))))
                .AddModifiers(
                    Token(SyntaxKind.PublicKeyword),
                    Token(SyntaxKind.StaticKeyword),
                    Token(SyntaxKind.ReadOnlyKeyword))
                .AddAttributeLists(
                    AttributeList(SingletonSeparatedList(
                        Attribute(IdentifierName("global::System.ComponentModel.EditorBrowsable")).AddArgumentListArguments(
                        AttributeArgument(ParseExpression("global::System.ComponentModel.EditorBrowsableState.Never"))))),
                    AttributeList(SingletonSeparatedList(
                        Attribute(IdentifierName("global::System.Obsolete")).AddArgumentListArguments(
                        AttributeArgument(LiteralExpression(
                            SyntaxKind.StringLiteralExpression,
                            Literal("This field is not intended to be referenced directly by user code")))))));
        }

        /// <summary>
        /// Get the generated property name for an input field.
        /// </summary>
        /// <param name="fieldSymbol">The input <see cref="IFieldSymbol"/> instance to process.</param>
        /// <returns>The generated property name for <paramref name="fieldSymbol"/>.</returns>
        public static string GetGeneratedPropertyName(IFieldSymbol fieldSymbol)
        {
            string propertyName = fieldSymbol.Name;

            if (propertyName.StartsWith("m_"))
            {
                propertyName = propertyName.Substring(2);
            }
            else if (propertyName.StartsWith("_"))
            {
                propertyName = propertyName.TrimStart('_');
            }

            return $"{char.ToUpper(propertyName[0])}{propertyName.Substring(1)}";
        }
    }
}