Join IEnumerable defaults with separator instead of space

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
68/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
csharp
Domain
cli

Research direction

Start in src/CommandLine/Text/HelpText.cs around line 1125, where default IEnumerable values are formatted for help output. Trace how the option's configured separator is available during formatting, then verify the sample's --help output uses commas between AAA, BBB, and CCC so the displayed default can be copied as an argument.

Written by the indexing model from the issue text.

Description

Source:

#:package CommandLineParser@2.9.1

using CommandLine;

return Parser.Default.ParseArguments<Opts>(args).MapResult(
	(Opts opts) => 0,
	errors => 2
);

class Opts {
    [Option("opt", Required = true, Separator = ',', Default = new[] { "AAA", "BBB", "CCC" }, HelpText = "boolean arg.")]
    public IEnumerable<string> MyOption { get; set; }
}

Output with --help:

test_cmdline 1.0.0
Copyright (C) 2026 test_cmdline

  --opt        Required. (Default: AAA BBB CCC) boolean arg.

  --help       Display this help screen.

  --version    Display version information.

Notice that the default argument's values are joined by spaces, which is misleading.
Since a separator is provided it should be used instead, so that the user could just copy-paste the resulting value directly and use it as argument. Currently there is no way to achieve this: see here.

Dominant language
C#
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