Semi-complex arg! macro invocation causes stack overflow and huge slowdown with build, check, or clippy

[TED-996]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

Rust Version

rustc 1.66.1 (90743e729 2023-01-10)

Clap Version

4.1.3

Minimal reproducible code

fn main() {
    let _ = clap::arg!(--add-b-alias <ALIAS> <NAME> ...);
}

Steps to reproduce the bug with the above code

cargo check

Actual Behaviour

The check command takes an unreasonably long amount of time to complete (around 10 seconds on my machine for the repro code alone). cargo build and cargo clippy similarly take an unreasonably long time to complete.

When running, the program overflows the stack.

Expected Behaviour

The check command should complete in a very short amount of time (less than one second). cargo build and cargo clippy should take a relatively short time as well.

When running, the program should execute to completion.

Additional Context

It seems like the combination of a three-word option name, num_args/value_names and multiple values (...) is relevant. The following examples all take a more reasonable amount of time:

    let _ = clap::arg!(--add-alias <ALIAS> <NAME> ...);  // this is better (~1s on my machine)
    let _ = clap::arg!(--add-b-alias <ALIAS> <NAME>);    // this is much better (.7s on my machine)
    let _ = clap::arg!(--add-b-alias ...);               // this is also much better (.5s on my machine)

I have worked around the problem by building the Arg struct manually. However this makes the arg! macro unusable for me - the editor experience is destroyed because with checking slowed down so much, even syntax higlighting is broken.

Debug Output

thread 'main' has overflowed its stack

[TED-996]

Updated title, the repro code causes a stack overflow without the debug feature as well, at least on Windows.

[epage]

#4673 should hopefully speed up compilation,.

#3524 is our main stack overflow issue for arg!

One thing to note is that --add-b-alias is actually parsed as --add -b -alias by the macro machinery. You need to do --"add-b-alias" to make the macro machinery understand it correctly.

[TED-996]

Thank you! I've missed that part of the documentation, sorry! The quotes do indeed fix the stack overflow and compile time issues.

[epage]

As we have other issues for stack overfows, I'm going to close this out