Document using @main to designate the root command

[natecook1000]

ArgumentParser projects built using Swift PM or Xcode can now use the @main attribute to designate the root command instead of calling Example.main(). We should document that usage as the correct default approach.

[eaigner]

Except when I try to use @main it complains with

'main' attribute cannot be used in a module that contains top-level code

[MPLew-is]

'main' attribute cannot be used in a module that contains top-level code

This error occurs when you have a main.swift; a top-level file and the @main attribute are mutually exclusive.

[sergiocampama]

you can rename main.swift to entry.swift or something to get around that...

[jaredh159]

I still can't figure out how to get this to work -- If i rename main.swift, i just get

executable product 'Example' expects target 'Example' to be executable; an executable target requires a 'main.swift' file

[el-hoshino]

↑Same here

[Ceylo]

For me the solution was to rename main.swift into something else while keeping @main. At first I had @main in main.swift which caused the error.

[Jerry-Carter]

I'm using Xcode 13.2 beta (13C5066c) on the async branch. I found that using

Task {
await program.run()
}

did not actually wait for the task to complete. Instead, I (1) dropped the program.run() call at the top level, (2) renamed 'main.swift' to something else (e.g. command.swift) and (3) added a '@main' annotation to the ParsableCommand derived structure.

[natecook1000]

The documentation updates with 1.1.0 address this issue.