System.CommandLine Command custom validator: how to search

Question

I am writing a C# console application project (.NET 7.0) using Visual Studio for macOS 2022 v17.4 and System.CommandLine (2.0.0-beta4.22272.1).

I am trying to add a custom validator to one of my Commands, and found the following code snippet on the project's GitHub site:

        this.AddValidator(commandResult =>
        {
            if (commandResult.Children.Contains("one") &&
                commandResult.Children.Contains("two"))
            {
               commandResult.ErrorMessage = "Options '--one' and '--two' cannot be used together.";
            }
        });

However, it will not compile in my command, due to Error CS1929: 'IReadOnlyList' does not contain a definition for 'Contains' and the best extension method overload 'MemoryExtensions.Contains(ReadOnlySpan, string)' requires a receiver of type 'ReadOnlySpan' (CS1929).

I have looked for the appropriate extension method in the various System.CommandLine namespaces, but I don't see anything. (Yes, I included the System.Linq namespace.)

Can anyone suggest what is amiss?

Edit: The original code which I "borrowed" is this:

        command.AddValidator(commandResult =>
        {
            if (commandResult.Children.Contains("one") &&
                commandResult.Children.Contains("two"))
            {
                return "Options '--one' and '--two' cannot be used together.";
            }

            return null;
        });

Note that this delegate returns a value, while the updated one does not, but instead sets ErrorMessage. That's one breaking change in System.CommandLine, and it's plausible that the issue here is due to another breaking change. The System.CommandLine project does note that the project is in a state of flux and subject to changes.

Does your code include the line `using System.Linq;`? – Ann L. Dec 27 '22 at 18:49 — Ann L., Dec 27 '22 at 18:49
Yes, it includes System.Linq. – R.J. Dunnill Dec 27 '22 at 18:58 — R.J. Dunnill, Dec 27 '22 at 18:58

SSS · Accepted Answer · 2022-12-27T19:28:13.063

I have no experience with this specific library, but peeking its source hints that the collection you are calling .Contains() on doesn't contain Strings, but rather instances of SymbolResult, hence it cannot find suitable overload for the method you are trying to call.

I couldn't find the code you provided anywhere from mentioned GitHub repo, but instead found this piece of code from this test file of library:

command.Validators.Add(commandResult =>
{
    if (commandResult.Children.Any(sr => sr.Symbol is IdentifierSymbol id && id.HasAlias("--one")) &&
        commandResult.Children.Any(sr => sr.Symbol is IdentifierSymbol id && id.HasAlias("--two")))
        {
            commandResult.ErrorMessage = "Options '--one' and '--two' cannot be used together.";
        }
});

My issue is possibly to a breaking change. System.CommandLine is, as the project managers note, in a state of flux. — R.J. Dunnill, Dec 27 '22 at 19:52

score 1 · Answer 2 · answered Dec 27 '22 at 18:52

1

The extension method you need is defined as part of the class System.Linq.Enumerable. So you need using System.Linq; at the top of your class file.

But that won't help if your project doesn't reference the assembly System.Linq.dll. (I don't know why it wouldn't, just out of the box, but perhaps it doesn't.) So you may need to add a reference for that.

answered Dec 27 '22 at 18:52

Ann L.

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I added a reference to NuGet package System.Linq 4.3.0, but still no luck. – R.J. Dunnill Dec 27 '22 at 19:06

System.CommandLine Command custom validator: how to search

2 Answers2