Remove Argument.AllowedValues, use Validator to implement the logic

[adamsitnik]

follow up to #1891 (comment)

[adamsitnik]

This change is not obvious. Before this change, the SymbolResult of ParseError for an Argument with unmatched tokens owned by an Option was the OptionResult, not ArgumentResult:

command-line-api/src/System.CommandLine/Parsing/ParseResultVisitor.cs

Line 509 in 0adeb26

argumentResult.Parent?.UnrecognizedArgumentError(argument) ??

but this was true only "non-custom errors" (user defined, coming from validators):

command-line-api/src/System.CommandLine/Parsing/ParseResultVisitor.cs

Line 510 in 0adeb26

argumentResult.CustomError(argument);

Without this change, one test was failing:

  Failed System.CommandLine.Tests.ParseDiagramTests.Parse_result_diagram_displays_unmatched_tokens [283 ms]
  Error Message:
   Expected string to be
"[ command ![ -x <ar> ] ]", but
"[ command [ -x !<ar> ] ]" differs near "[ -" (index 10).

Since we hide the Option.Argument from the user, I think it's reasonable to use the OptionResult in such cases for all validations.

[KalleOlaviNiemitalo]

AcceptOnlyFromAmong is case-sensitive, unlike the Enum.Parse call in ArgumentConverter

command-line-api/src/System.CommandLine/Binding/ArgumentConverter.cs

Line 61 in 209b724

return Success(argument, Enum.Parse(type, value, true));

, so it is not a good method for restricting which enum values can be used. This PR kind of improves the situation by making AcceptOnlyFromAmong use the same features that are in the public API, so an app developer can more easily imitate this when implementing a case-insensitive variant.

[jonsequitur]

If there's no test for case-insensitive enum parsing, we should definitely add one.

[jozkee]

There are other places that call Validator.Add, which would now add the Action to the Array.Empty<Action>.

command-line-api/src/System.CommandLine/Argument{T}.cs

Line 215 in 350a618

Validators.Add(validate);

command-line-api/src/System.CommandLine/OptionValidation.cs

Line 21 in 350a618

option.Argument.Validators.Add(Validate.FileExists);

[jozkee]

Now that #1966 is merged, this shoud go on Argument<T>.

[adamsitnik]

I've addressed all the feedback, I am going to merge this PR now to unblock other PRs.

AcceptOnlyFromAmong is case-sensitive, unlike the Enum.Parse call in ArgumentConverter

Please create an issue for that. We can just extend AcceptOnlyFromAmong with an StringComparison comparisonType argument and let the users decide

[KalleOlaviNiemitalo]

Please create an issue for that.

Already created #1960 a month ago.

We can just extend AcceptOnlyFromAmong with an StringComparison comparisonType argument and let the users decide

Users can easily implement AcceptOnlyFromAmong(string[], StringComparison) on their own, so I don't think the library needs to provide that. For enums though, users are more likely to get the validation wrong, because it is not evident from the method signatures that the parsing will be case-insensitive.