UseAutoPropertyCodeFixProvider.cs

// Copyright (c) .NET Foundation and Contributors. Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System.Collections.Immutable;
using System.Composition;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Roslynator.CodeFixes;
using Roslynator.CSharp;
using static Microsoft.CodeAnalysis.CSharp.SyntaxFactory;
using static Roslynator.CSharp.CSharpFactory;

namespace Roslynator.CSharp.CodeFixes;

[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(UseAutoPropertyCodeFixProvider))]
[Shared]
public sealed class UseAutoPropertyCodeFixProvider : BaseCodeFixProvider
{
    private static readonly SyntaxAnnotation _removeAnnotation = new();

    public override ImmutableArray<string> FixableDiagnosticIds
    {
        get { return ImmutableArray.Create(DiagnosticIdentifiers.UseAutoProperty); }
    }

    public override async Task RegisterCodeFixesAsync(CodeFixContext context)
    {
        SyntaxNode root = await context.GetSyntaxRootAsync().ConfigureAwait(false);

        if (!TryFindFirstAncestorOrSelf(root, context.Span, out PropertyDeclarationSyntax property))
            return;

        Diagnostic diagnostic = context.Diagnostics[0];

        CodeAction codeAction = CodeAction.Create(
            "Use auto-property",
            ct => RefactorAsync(context.Document, property, ct),
            GetEquivalenceKey(diagnostic));

        context.RegisterCodeFix(codeAction, diagnostic);
    }

    public static async Task<Document> RefactorAsync(
        Document document,
        PropertyDeclarationSyntax propertyDeclaration,
        CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();

        SyntaxToken propertyIdentifier = propertyDeclaration.Identifier.WithoutTrivia();

        SemanticModel semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);

        IPropertySymbol propertySymbol = semanticModel.GetDeclaredSymbol(propertyDeclaration, cancellationToken);

        ISymbol fieldSymbol = GetFieldSymbol(propertyDeclaration, semanticModel, cancellationToken);

        var variableDeclarator = (VariableDeclaratorSyntax)await fieldSymbol.GetSyntaxAsync(cancellationToken).ConfigureAwait(false);

        var variableDeclaration = (VariableDeclarationSyntax)variableDeclarator.Parent;

        var fieldDeclaration = (FieldDeclarationSyntax)variableDeclaration.Parent;

        bool isSingleDeclarator = variableDeclaration.Variables.Count == 1;

        ImmutableArray<SyntaxNode> nodes = await SyntaxFinder.FindReferencesAsync(fieldSymbol, document, allowCandidate: false, cancellationToken: cancellationToken).ConfigureAwait(false);

        nodes = nodes.Add(propertyDeclaration);

        if (isSingleDeclarator)
        {
            nodes = nodes.Add(fieldDeclaration);
        }
        else
        {
            nodes = nodes.Add(variableDeclarator);
        }

        SyntaxNode root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);

        SyntaxNode newRoot = root.ReplaceNodes(
            nodes,
            (node, _) =>
            {
                switch (node.Kind())
                {
                    case SyntaxKind.IdentifierName:
                        {
                            SyntaxNode newNode = null;

                            if (node.IsParentKind(SyntaxKind.SimpleMemberAccessExpression)
                                && ((MemberAccessExpressionSyntax)node.Parent).Name == node)
                            {
                                newNode = IdentifierName(propertyIdentifier);
                            }
                            else if (node.IsParentKind(SyntaxKind.NameMemberCref))
                            {
                                newNode = IdentifierName(propertyIdentifier);
                            }
                            else if (propertySymbol.IsStatic)
                            {
                                newNode = SimpleMemberAccessExpression(
                                    propertySymbol.ContainingType.ToTypeSyntax(),
                                    (SimpleNameSyntax)ParseName(propertySymbol.ToDisplayString(SymbolDisplayFormats.DisplayName)))
                                    .WithSimplifierAnnotation();
                            }
                            else
                            {
                                newNode = IdentifierName(propertyIdentifier).QualifyWithThis();
                            }

                            return newNode.WithTriviaFrom(node);
                        }
                    case SyntaxKind.PropertyDeclaration:
                        {
                            return CreateAutoProperty(propertyDeclaration, variableDeclarator.Initializer);
                        }
                    case SyntaxKind.VariableDeclarator:
                    case SyntaxKind.FieldDeclaration:
                        {
                            return node.WithAdditionalAnnotations(_removeAnnotation);
                        }
                    default:
                        {
                            SyntaxDebug.Fail(node);
                            return node;
                        }
                }
            });

        SyntaxNode nodeToRemove = newRoot.GetAnnotatedNodes(_removeAnnotation).FirstOrDefault();

        if (nodeToRemove is not null)
            newRoot = newRoot.RemoveNode(nodeToRemove, SyntaxRemoveOptions.KeepUnbalancedDirectives);

        return document.WithSyntaxRoot(newRoot);
    }

    private static ISymbol GetFieldSymbol(PropertyDeclarationSyntax property, SemanticModel semanticModel, CancellationToken cancellationToken)
    {
        ArrowExpressionClauseSyntax expressionBody = property.ExpressionBody;

        if (expressionBody is not null)
        {
            return semanticModel.GetSymbol(expressionBody.Expression, cancellationToken);
        }
        else
        {
            AccessorDeclarationSyntax getter = property.Getter();

            BlockSyntax body = getter.Body;

            if (body is not null)
            {
                var returnStatement = (ReturnStatementSyntax)body.Statements[0];

                return semanticModel.GetSymbol(returnStatement.Expression, cancellationToken);
            }
            else
            {
                return semanticModel.GetSymbol(getter.ExpressionBody.Expression, cancellationToken);
            }
        }
    }

    public static PropertyDeclarationSyntax CreateAutoProperty(PropertyDeclarationSyntax property, EqualsValueClauseSyntax initializer)
    {
        AccessorListSyntax accessorList = property.AccessorList;

        if (accessorList is not null)
        {
            SyntaxList<AccessorDeclarationSyntax> newAccessors = accessorList
                .Accessors
                .Select(accessor =>
                {
                    accessor = accessor.Update(
                        attributeLists: accessor.AttributeLists,
                        modifiers: accessor.Modifiers,
                        keyword: accessor.Keyword,
                        body: default(BlockSyntax),
                        expressionBody: default(ArrowExpressionClauseSyntax),
                        semicolonToken: Token(default, SyntaxKind.SemicolonToken, TriviaList(NewLine())));

                    return accessor.WithTriviaFrom(accessor);
                })
                .ToSyntaxList();

            accessorList = accessorList.WithAccessors(newAccessors);
        }
        else
        {
            accessorList = AccessorList(AutoGetAccessorDeclaration().WithTrailingTrivia(NewLine()))
                .WithTriviaFrom(property.ExpressionBody);
        }

        if (accessorList.Accessors.All(f => !f.AttributeLists.Any())
            && accessorList.DescendantTrivia().All(f => f.IsWhitespaceOrEndOfLineTrivia()))
        {
            accessorList = accessorList.RemoveWhitespace();
        }

        PropertyDeclarationSyntax newProperty = property.Update(
            attributeLists: property.AttributeLists,
            modifiers: property.Modifiers,
            type: property.Type,
            explicitInterfaceSpecifier: property.ExplicitInterfaceSpecifier,
            identifier: property.Identifier.WithTrailingTrivia(Space),
            accessorList: accessorList,
            expressionBody: default(ArrowExpressionClauseSyntax),
            initializer: initializer,
            semicolonToken: (initializer is not null) ? SemicolonToken() : default);

        return newProperty
            .WithTriviaFrom(property)
            .WithFormatterAnnotation();
    }
}