Print default toolchain on rustup default without arguments

[das-sein]

Implementation of #1632

Behavior: When rustup default is not provided arguments, print the default toolchain (new behavior) before commencing updates of all installed toolchains.

[dwijnand]

Hey, @lazorgator. Thanks for sending the PR. Want to update the tests so we can assess how this implementation behaves?

[das-sein]

Yep, sorry about that! Working on them now for both PRs.

[das-sein]

@dwijnand Should be all set. I only needed to modify one test. However, I noticed that it was possible to be in a state wherein no default toolchain was set in the settings. This required modification of the config.get_default() behavior very slightly. It doesn't seem to affect how the rest of the software expects that method to work. Without the modification it would throw an exception about trying to unwrap() a None during the rustup_self_update_exact test.

[dwijnand]

Thanks, @lazorgator. The patch seems reasonable to me. I'd merge it if I could. So let's see if this matches @nrc's expectations in #1632.

[dwijnand]

r? @nrc

[nrc]

I'm very sorry, but I messed up and wrote update when I meant default in #1632 . Could you change this PR to printing the same message but on the different command please?

[das-sein]

@nrc Alright, added the functionality to rustup default as well! If you want me to remove the functionality from rustup update, let me know.

[dwijnand]

Perhaps it's best to remove it from rustup update.

[das-sein]

@dwijnand @nrc Should be all set, I think. Functionality removed from rustup update.

[dwijnand]

Re-LGTM

[nrc]

Awesome, thanks!

[dwijnand]

Does this duplicate rustup show active-toolchain?

[das-sein]

@dwijnand It does I think! I'll work on a PR to just make the rustup default behavior an alias to that command, if possible. rustup show active-toolchain also deals with the override display issue.