CliFx/CliFx.Analyzers/ParameterMustBeSingleIfNonScalarAnalyzer.cs

using System.Linq;
using CliFx.Analyzers.ObjectModel;
using CliFx.Analyzers.Utils.Extensions;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Diagnostics;

namespace CliFx.Analyzers
{
    [DiagnosticAnalyzer(LanguageNames.CSharp)]
    public class ParameterMustBeSingleIfNonScalarAnalyzer : AnalyzerBase
    {
        public ParameterMustBeSingleIfNonScalarAnalyzer()
            : base(
                "Parameters of non-scalar types are limited to one per command",
                "This parameter has a non-scalar type so it must be the only such parameter in the command.")
        {
        }

        private static bool IsScalar(ITypeSymbol type) =>
            type.DisplayNameMatches("string") ||
            type.DisplayNameMatches("System.String") ||
            !type.AllInterfaces
                .Select(i => i.ConstructedFrom)
                .Any(s => s.DisplayNameMatches("System.Collections.Generic.IEnumerable<T>"));

        private void Analyze(
            SyntaxNodeAnalysisContext context,
            PropertyDeclarationSyntax propertyDeclaration,
            IPropertySymbol property)
        {
            if (property.ContainingType is null)
                return;

            if (!CommandParameterSymbol.IsParameterProperty(property))
                return;

            if (IsScalar(property.Type))
                return;

            var otherProperties = property
                .ContainingType
                .GetMembers()
                .OfType<IPropertySymbol>()
                .Where(m => !m.Equals(property, SymbolEqualityComparer.Default))
                .ToArray();

            foreach (var otherProperty in otherProperties)
            {
                if (!CommandParameterSymbol.IsParameterProperty(otherProperty))
                    continue;

                if (!IsScalar(otherProperty.Type))
                {
                    context.ReportDiagnostic(CreateDiagnostic(propertyDeclaration.GetLocation()));
                }
            }
        }

        public override void Initialize(AnalysisContext context)
        {
            base.Initialize(context);
            context.HandlePropertyDeclaration(Analyze);
        }
    }
}