No way to mark a single-value argument as required #2392

Checklist

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What problem does this solve?

Version: urfave/cli v3.10.1 (also on latest main at commit 4937c16)

There is no way to require a single-value argument ({Type}Arg). ArgumentBase.Parse falls back to the default value when no argument is given, so a command like app delete runs with an empty ID instead of failing.

The closest workaround is the plural type with Min/Max:

var ids []string

&cli.StringArgs{Name: "id", Min: 1, Max: 1, Destination: &ids}

which needs a slice destination for a single value, and shows this when the argument is missing:

sufficient count of arg id not provided, given 0 expected 1

Solution description

The same thing flags already have (FlagBase.Required):

&cli.StringArg{Name: "id", Required: true, Destination: &id}

With Required: true, Parse returns Required argument "id" not set when the argument is missing.

Help output could also follow the bracket convention that {Type}Args already uses: [name] when optional, name when required. Today single args always render as name even though they are optional. This changes the expectation in TestArgUsage from ia to [ia]; no other test encodes the current rendering.

Describe alternatives you've considered

Making ArgumentBase.Parse error when the argument is missing, without a new field. That would be a breaking change — the fallback to Value is intentional (TestSingleOptionalArg).

A Min field like the plural type has. On a single value it can only ever be 0 or 1, so a bool seemed like a better fit.