How to write codefix that adds an argument to method call?

[miroslav77]

How to write a codefix that will offer to rewrite expression

JObject.Parse(json);
to
JObject.Parse(json, new JsonLoadSettings { DuplicatePropertyNameHandling = DuplicatePropertyNameHandling.Error });'

How are attributes added to expressions?

[CyrusNajmabadi]

Take a look at what both syntax trees look like. Your fixer will have to transform the tree shape of the first to the second.

Hre, this would involve adding an:

Argument, that contains an
ObjectCreationExpression, that contains an
Initializer, that contains an
AssignmentExpression, that contains a Left and Right side.

[miroslav77]

I think I did it. It looks like this:

public sealed override Task RegisterCodeFixesAsync(CodeFixContext context)
{
    context.RegisterCodeFix(
        CodeAction.Create(
            title: "Add DuplicatePropertyNameHandling.None",
            createChangedDocument: c => AddDuplicatePropertyNameHandlingNoneAsync(context.Document, context.Span, c),
            equivalenceKey: "AddDuplicatePropertyNameHandlingNone"),
        context.Diagnostics);

    return Task.CompletedTask;
}

        private async Task<Document> AddDuplicatePropertyNameHandlingNoneAsync(Document document, TextSpan span, CancellationToken cancellationToken)
{
    var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
    var node = root.FindNode(span);

    if (node is InvocationExpressionSyntax invocationExpressionSyntax)
    {
        // Ensure that the method has only one argument
        if (invocationExpressionSyntax.ArgumentList.Arguments.Count == 1)
        {
            // Add the additional argument to the method's argument list
            var a1 = SyntaxFactory.ParseArgumentList("new JsonLoadSettings { DuplicatePropertyNameHandling = DuplicatePropertyNameHandling.Error }").Arguments[0];
            
            var newArgumentList = invocationExpressionSyntax.ArgumentList.AddArguments(a1);

            // Create a new method invocation with the updated argument list
            var newMethodInvocation = invocationExpressionSyntax.WithArgumentList(newArgumentList);

            // Update the syntax tree with the new method invocation
            var newRoot = root.ReplaceNode(invocationExpressionSyntax, newMethodInvocation);
            return document.WithSyntaxRoot(newRoot);
        }
    }

    return document; // Return the original document if the code fix couldn't be applied
}

[sharwell]

var a1 = SyntaxFactory.ParseArgumentList("new JsonLoadSettings { DuplicatePropertyNameHandling = DuplicatePropertyNameHandling.Error }").Arguments[0];

The argument list in quotes would need to be parethesized for this to work, right?