Providing a token to `cargo login` via command line causes a hang on CI

[DrChat]

Problem

Specifying the logon token via the command-line will cause a hang if stdin is not attached to a terminal (such as when running in automation).

Steps

cargo login --registry xxxxxxxx "Bearer XXXXXXXXXXXXXXXXXXXXXXXXX"

Possible Solution(s)

Workaround:

"Bearer XXXXXXXXXXXXXXXXXXXXXXXXX" | cargo login --registry xxxxxxxx

Notes

Likely introduced by #12334:

cargo/src/cargo/ops/registry/login.rs

Lines 38 to 44 in 263d24b

	if !std::io::stdin().is_terminal() {
	let token = std::io::read_to_string(std::io::stdin()).unwrap_or_default();
	if !token.is_empty() {
	token_from_stdin = Some(token);
	}
	}
	let token = token_from_cmdline.or_else(|| token_from_stdin.as_deref().map(Secret::from));

Version

cargo 1.73.0-nightly (c91a693e7 2023-07-31)
release: 1.73.0-nightly
commit-hash: c91a693e7977e33a1064b63a5daf5fb689f01651
commit-date: 2023-07-31
host: x86_64-unknown-linux-gnu
libgit2: 1.6.4 (sys:0.17.2 vendored)
libcurl: 8.2.1-DEV (sys:0.4.65+curl-8.2.1 vendored ssl:OpenSSL/1.1.1u)
ssl: OpenSSL 1.1.1u  30 May 2023
os: Ubuntu 20.04 (focal) [64-bit]

[ehuss]

@arlosi Do you have a chance to look at this? I think an easy change would be to move the is_terminal check into the or_else closure.

I'm a bit unclear why CI has a stdin that isn't /dev/null and isn't a terminal. I would expect non-terminal stdin to immediately return an empty input.