system-commandline-net-3x-additions

name	system-commandline-net-3x-additions
version	3.0.0
description	Use when targeting System.CommandLine 3.x specifically — the members added over 2.x GA (Argument<T>.CaptureRemainingTokens, the AcceptOnlyFromAmong(StringComparer,...) overload, RootCommand.HelpName) and the current TFM targeting (net10.0 + netstandard2.0, no in-box net8.0). 3.x is additive over 2.x: existing 2.x code compiles unchanged.

System.CommandLine: 3.x additions over 2.x

3.x is additive over 2.x GA — no breaking changes. Upgrading 2.x → 3.x is a version bump with no code changes; do not "modernize" working 2.x code. This skill lists what 3.x adds and the current targeting.

Do NOT web_search / web_fetch. These skills are the current API; this one covers only the 3.x-specific delta.

Required setup

3.x is a package version bump — <PackageReference Include="System.CommandLine" Version="3.0.0-preview.6.26359.118" /> (or dotnet package add <proj> System.CommandLine). It is not in the shared framework. The namespace is unchanged: using System.CommandLine;.

The members below attach the same way as any other input — declare the instance, add it to a command, read it back by that instance:

using System.CommandLine;

var root = new RootCommand("My tool");
// ... add options/arguments to root.Options / root.Arguments, then:
return await root.Parse(args).InvokeAsync();

New members

// 1. Greedy trailing argument — captures ALL remaining tokens (e.g. pass-through args):
var forwarded = new Argument<string[]>("args") { CaptureRemainingTokens = true };
runCmd.Arguments.Add(forwarded);
// $ tool run -- --any --thing here   ->  GetValue(forwarded) == ["--any","--thing","here"]

// 2. Case-insensitive constrained values — the StringComparer overload is new in 3.x
//    (the params-string-only overload already existed in 2.x):
var level = new Option<string>("--level");
level.AcceptOnlyFromAmong(StringComparer.OrdinalIgnoreCase, "debug", "info", "warn");

// 3. Custom program name in help/usage output:
var root = new RootCommand("My tool") { HelpName = "mytool" };

Targeting

• The package targets net10.0 and netstandard2.0. The in-box net8.0 target was dropped — that is the only consumer-visible shift going 2.x → 3.x.
• Add it like any package: <PackageReference Include="System.CommandLine" Version="3.0.0-preview.6.26359.118" /> (or dotnet package add <proj> System.CommandLine). It is not in the shared framework.

Upgrading 2.x → 3.x

Bump the version, change no code. If you are coming from a 2.0.0-beta, that IS a breaking migration — apply the beta→GA rename map first (covered separately), then optionally adopt the members above.