Roslyn Analyzer for String comparison

Question

I want to write a roslyn analyzer for string comparison. The cases are: s1 can be a string. So if s1.equals(s2) or s1 == s2; it should fix to string.equals(s1,s2,Stringcomparsion.Ordinal)

I got the basic understanding of tree and also i need to create a Analyzer file and a CodeFixProvider class.

So I tried to get the syntax tree for eg. s1.equals(s2).

Now for writing the Analyze code method, I do not know how to verify the s1 is either a string. So i need help here.

I am trying to follow this article, https://www.meziantou.net/writing-a-roslyn-analyzer.htm .

For eg.

Class{
  string s1 = "one";
  string s2 = "two";
  bool res = one.equals(two);
}

should refactor to:

Class{
  string s1 = "one";
  string s2 = "two";
  bool res = string.equals(one,two, StringComparsion.Ordinal);
}

Answer 1

You can check the implementation of the rule MA0006: GitHub

You can also check my post about string comparisons for other analyzers for strings: https://www.meziantou.net/string-comparisons-are-harder-than-it-seems.htm#getting-warnings-in

    [DiagnosticAnalyzer(LanguageNames.CSharp)]
    public sealed class UseStringEqualsAnalyzer : DiagnosticAnalyzer
    {
        public override void Initialize(AnalysisContext context)
        {
            context.EnableConcurrentExecution();
            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);

            context.RegisterOperationAction(AnalyzeInvocation, OperationKind.BinaryOperator);
        }

        private static void AnalyzeInvocation(OperationAnalysisContext context)
        {
            var operation = (IBinaryOperation)context.Operation;
            if (operation.OperatorKind == BinaryOperatorKind.Equals ||
                operation.OperatorKind == BinaryOperatorKind.NotEquals)
            {
                if (operation.LeftOperand.Type.IsString() && operation.RightOperand.Type.IsString())
                {
                    if (IsNull(operation.LeftOperand) || IsNull(operation.RightOperand))
                        return;

                    // EntityFramework Core doesn't support StringComparison and evaluates everything client side...
                    // https://github.com/aspnet/EntityFrameworkCore/issues/1222
                    if (operation.IsInExpressionArgument())
                        return;

                    context.ReportDiagnostic(s_rule, operation, $"{operation.OperatorKind} operator");
                }
            }
        }

        private static bool IsNull(IOperation operation)
        {
            return operation.ConstantValue.HasValue && operation.ConstantValue.Value == null;
        }
    }

Answer 2

Note that if you're just looking to have this analyzer to run on your own code and less interested in actually writing it, this is already implemented in the Microsoft-written analyzers:

https://docs.microsoft.com/en-us/visualstudio/code-quality/ca1307

Instructions for installation are available here:

https://github.com/dotnet/roslyn-analyzers#microsoftcodeanalysisfxcopanalyzers

Our code for it is also available, but @meziantou's answer is a good example if you do want the simple code to start to understand analyzers.