Restrict attribute to only one property per class

Is there a way of ensuring that an attribute marked with [AttributeUsage(AttributeTargets.Property)] is used maximum once per class?

In other words, either 0 or 1 properties should be decorated with a particular attribute, never more than 1. Can this be done?

You can create your own analyzer, compile it into dll and include in your project.

Let's start with "tests" to ensure everything works as you expect:

Single property - class compiles

Second property - class does not compile

Second attribute type - different attributes work together and compile

Attributes are counted independently - does not compile if any of those exist more than once in a class

Analyzer error message

Here is analyzer code. It goes over csharp syntax, counts properties with attributes that are marked with AttributeUsageAttribute and have flag AttributeTargets.Property

using System.Collections.Immutable;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Diagnostics;
[DiagnosticAnalyzer(LanguageNames.CSharp)]
public class PropertyAttributeAnalyzer : DiagnosticAnalyzer
{
private const string Category = "Usage";
private static DiagnosticDescriptor Rule = new DiagnosticDescriptor(
"PA001",
"Multiple Properties with Attribute",
"Multiple properties with the attribute '{0}' are found in the class",
Category,
DiagnosticSeverity.Error,
isEnabledByDefault: true);
public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(Rule);
public override void Initialize(AnalysisContext context)
{
context.RegisterSyntaxNodeAction(AnalyzeClassSyntax, SyntaxKind.ClassDeclaration);
}
private static void AnalyzeClassSyntax(SyntaxNodeAnalysisContext context)
{
var classDeclaration = (ClassDeclarationSyntax)context.Node;
var occurrences = new Dictionary<string, int>();
foreach (var property in classDeclaration.Members.OfType<PropertyDeclarationSyntax>())
{
var attributes = property.AttributeLists.SelectMany(list => list.Attributes);
foreach (var attribute in attributes)
{
if (!IsDesiredAttribute(context, classDeclaration, attribute))
continue;
if (occurrences.ContainsKey(attribute.Name.ToString()))
{
occurrences[attribute.Name.ToString()]++;
}
else
{
occurrences[attribute.Name.ToString()] = 1;
}
}
}
foreach (var attribute in occurrences.Where(x => x.Value > 1))
{
var diagnostic = Diagnostic.Create(Rule, classDeclaration.Identifier.GetLocation(), attribute.Key);
context.ReportDiagnostic(diagnostic);
}
}
private static bool IsDesiredAttribute(SyntaxNodeAnalysisContext context, ClassDeclarationSyntax classDeclaration, AttributeSyntax attributeSyntax)
{
var semanticModel = context.SemanticModel;
var attributeSymbol = semanticModel.GetSymbolInfo(attributeSyntax).Symbol;
var attributeType = attributeSymbol?.ContainingType;
if (attributeType is null)
return false;
var attributeUsageAttribute = semanticModel.Compilation.GetTypeByMetadataName(typeof(AttributeUsageAttribute).FullName);
var attributeUsage = attributeType.GetAttributes().FirstOrDefault(attr => attr.AttributeClass.Equals(attributeUsageAttribute));
if (attributeUsage is null)
return false;
var validOnArgument = attributeUsage.ConstructorArguments.FirstOrDefault(arg => arg.Type?.Name == "AttributeTargets");
var validTargets = (AttributeTargets)(int)validOnArgument.Value;
return validTargets.HasFlag(AttributeTargets.Property);
}
}

You have to compile Analyzer and link its dll into your project's csproj file

<ItemGroup>
<Analyzer Include="C:\Users\Asus\RiderProjects\TestAnalyzer\Analyzer\bin\Debug\net7.0\Analyzer.dll"/>
</ItemGroup>

Finally, my solution structure