Possible bug in beta5 System.CommandLine API #2634

This issue has been moved from a ticket on Developer Community.

[severity:It’s more difficult to complete my work]
There is a Command.SetAction that takes a Func<ParseResult, Task>. I believe this should be Func<ParseResult, Task<int>>.

When converting from the old API, I ended up with an function that returns a Task<int>. This was silently passed to the Func<ParseResult, Task> version, which silently ate the return value and returned 0 instead.

Workaround: Use the override that also takes a cancellation token.

If you want to keep the Func<ParseResult, Task> version, that’s fine, as long as you also add a Func<ParseResult, Task<int>>. When this issue bit me during conversion from the old to the new API, it took some debugging to get to the bottom of.

Aside from that, the new API is a distinct improvement over the old one.

Original Comments

Feedback Bot on 7/4/2025, 04:24 AM:

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