Option to indicate update via exit code

[joshtriplett]

Problem you are trying to solve

I'd like to run rustup update stable and get an indication of whether stable actually updated, without parsing rustup's human-readable output.

Solution you'd like

I'd like to have an option to have rustup update set an exit code based on whether any of the requested toolchains had an update. (This shouldn't be the default, since that might cause workflows to fail when a no-op update occurs.)

Notes

No response

[rami3l]

@joshtriplett I guess we can align the exit status with #4681 (comment)?

[joshtriplett]

@rami3l Yes, check and update --check should use the same exit status. One difference is that update --check stable would only update stable and have its exit status only indicate whether there was an update to stable.

[21elias]

@rustbot claim