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// 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;
using System.Collections.Immutable;
using System.Composition;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeFixes;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;
namespace Microsoft.CodeAnalysis.CSharp.ReplaceDefaultLiteral;
[ExportCodeFixProvider(LanguageNames.CSharp, Name = PredefinedCodeFixProviderNames.ReplaceDefaultLiteral), Shared]
[method: ImportingConstructor]
[method: SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
internal sealed class CSharpReplaceDefaultLiteralCodeFixProvider() : CodeFixProvider
{
private const string CS8313 = nameof(CS8313); // A default literal 'default' is not valid as a case constant. Use another literal (e.g. '0' or 'null') as appropriate. If you intended to write the default label, use 'default:' without 'case'.
private const string CS8505 = nameof(CS8505); // A default literal 'default' is not valid as a pattern. Use another literal (e.g. '0' or 'null') as appropriate. To match everything, use a discard pattern 'var _'.
public override ImmutableArray<string> FixableDiagnosticIds { get; } = [CS8313, CS8505];
public override FixAllProvider? GetFixAllProvider()
{
// This code fix addresses very specific compiler errors. It's unlikely there will be more than 1 of them at a time.
return null;
}
public override async Task RegisterCodeFixesAsync(CodeFixContext context)
{
var syntaxRoot = await context.Document.GetRequiredSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
var token = syntaxRoot.FindToken(context.Span.Start);
if (token.Span == context.Span &&
token.IsKind(SyntaxKind.DefaultKeyword) &&
token.Parent is LiteralExpressionSyntax(SyntaxKind.DefaultLiteralExpression) defaultLiteral)
{
var semanticModel = await context.Document.GetRequiredSemanticModelAsync(context.CancellationToken).ConfigureAwait(false);
var (newExpression, displayText) = GetReplacementExpressionAndText(
context.Document, semanticModel, defaultLiteral, context.CancellationToken);
if (newExpression != null)
{
context.RegisterCodeFix(
CodeAction.Create(
string.Format(CSharpCodeFixesResources.Use_0, displayText),
c => ReplaceAsync(context.Document, context.Span, newExpression, c),
nameof(CSharpCodeFixesResources.Use_0)),
context.Diagnostics);
}
}
}
private static async Task<Document> ReplaceAsync(
Document document, TextSpan span, SyntaxNode newExpression, CancellationToken cancellationToken)
{
var syntaxRoot = await document.GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
var defaultToken = syntaxRoot.FindToken(span.Start);
var defaultLiteral = (LiteralExpressionSyntax)defaultToken.GetRequiredParent();
var newRoot = syntaxRoot.ReplaceNode(defaultLiteral, newExpression.WithTriviaFrom(defaultLiteral));
return document.WithSyntaxRoot(newRoot);
}
private static (SyntaxNode newExpression, string displayText) GetReplacementExpressionAndText(
Document document,
SemanticModel semanticModel,
LiteralExpressionSyntax defaultLiteral,
CancellationToken cancellationToken)
{
var generator = SyntaxGenerator.GetGenerator(document);
var type = semanticModel.GetTypeInfo(defaultLiteral, cancellationToken).ConvertedType;
if (type != null && type.TypeKind != TypeKind.Error)
{
if (IsFlagsEnum(type, semanticModel.Compilation) &&
type.GetMembers("None").FirstOrDefault() is IFieldSymbol field && IsZero(field.ConstantValue))
{
return GenerateMemberAccess("None");
}
else if (type.Equals(semanticModel.Compilation.GetTypeByMetadataName(typeof(CancellationToken).FullName!)))
{
return GenerateMemberAccess(nameof(CancellationToken.None));
}
else if (type.SpecialType is SpecialType.System_IntPtr or SpecialType.System_UIntPtr)
{
return GenerateMemberAccess(nameof(IntPtr.Zero));
}
else if (semanticModel.GetConstantValue(defaultLiteral, cancellationToken) is var constant && constant.HasValue)
{
var newLiteral = generator.LiteralExpression(constant.Value);
return (newLiteral, newLiteral.ToString());
}
else if (!type.ContainsAnonymousType())
{
var defaultExpression = generator.DefaultExpression(type);
return (defaultExpression, $"default({type.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat)})");
}
}
return default;
(SyntaxNode newExpression, string displayText) GenerateMemberAccess(string memberName)
{
var memberAccess = generator.MemberAccessExpression(generator.TypeExpression(type), memberName);
return (memberAccess, $"{type.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat)}.{memberName}");
}
}
private static bool IsFlagsEnum(ITypeSymbol type, Compilation compilation)
{
var flagsAttribute = compilation.GetTypeByMetadataName(typeof(FlagsAttribute).FullName!);
return type.TypeKind == TypeKind.Enum &&
flagsAttribute != null &&
type.HasAttribute(flagsAttribute);
}
private static bool IsZero(object? o)
{
switch (o)
{
case default(int):
case default(uint):
case default(byte):
case default(sbyte):
case default(short):
case default(ushort):
case default(long):
case default(ulong):
return true;
default:
return false;
}
}
}
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