Shell completion generation fails in loop with global flags/options

[Fleshgrinder]

Rust Version

N/A

Affected Version of clap

Probably all but 2.20.3 was the one where the bug was encountered.

Expected Behavior Summary

Build and compilation should succeed.

Actual Behavior Summary

Build fails with the following output:

$ cargo build
   Compiling mwe v0.1.0 (file:///D:/GitHub/rust-phpup)
error: failed to run custom build command for `mwe v0.1.0 (file:///D:/GitHub/rust-phpup)`
process didn't exit successfully: `D:\GitHub\rust-phpup\target\debug\build\mwe-563482c66f20550f\build-script-build` (exit code: 101)
--- stderr
thread 'main' panicked at 'Non-unique argument name: quiet is already in use', C:\Users\Fleshgrinder\.cargo\registry\src\github.com-1ecc6299db9ec823\clap-2.20.3\src\app\parser.rs:147
note: Run with `RUST_BACKTRACE=1` for a backtrace.

Steps to Reproduce the issue

cargo build the code linked in the Gist

Sample Code or Link to Sample Code

https://gist.github.com/Fleshgrinder/3b562bb6c91deb49635543e68f720651

Reason

The problem occurs due to gen_completion and build.rs where the app is reused in the loop as you discovered already in a short Gitter chat.

[kbknapp]

Thanks, as per our discussion on gitter, I shuold have this fixed soon 😄

[kbknapp]

Also, incase anyone else is running into this calling the gen_completions causes all global Args to be propogated, on second and further iterations of the loop, this causes duplicate Args to be built which is an error.

This is a bug, and those duplicate Args should be ignored in this case.

The temporary fix is to rebuild the App struct with each iteration of the loop (which takes nanoseconds, so isn't a big deal).

for shell in &[Shell::Bash, Shell::PowerShell] {
    let mut app = build_cli();
    app.gen_completions(env!("CARGO_PKG_NAME"), *shell, env!("OUT_DIR"));
}