`rustup show` should not force-install the default toolchain if it is not installed.

[johnthagen]

This behavior confused me:

$ rustup uninstall nightly-2018-04-01-x86_64-apple-darwin
info: uninstalling toolchain 'nightly-2018-04-01-x86_64-apple-darwin'
info: toolchain 'nightly-2018-04-01-x86_64-apple-darwin' uninstalled
$ rustup show
Default host: x86_64-apple-darwin

info: syncing channel updates for 'nightly-2018-04-01-x86_64-apple-darwin'
info: latest update on 2018-04-01, rust version 1.26.0-nightly (517f24025 2018-03-31)
info: downloading component 'rustc'
 57.3 MiB /  57.3 MiB (100 %)   7.8 MiB/s ETA:   0 s                
info: downloading component 'rust-std'
 46.2 MiB /  46.2 MiB (100 %)   7.4 MiB/s ETA:   0 s                
info: downloading component 'cargo'
  3.0 MiB /   3.0 MiB (100 %)   1.5 MiB/s ETA:   0 s                
info: downloading component 'rust-docs'
  6.8 MiB /   6.8 MiB (100 %)   3.1 MiB/s ETA:   0 s                
info: installing component 'rustc'
info: installing component 'rust-std'
info: installing component 'cargo'
info: installing component 'rust-docs'
installed toolchains
--------------------

stable-x86_64-apple-darwin
nightly-i686-apple-darwin
nightly-x86_64-apple-darwin (default)

active toolchain
----------------

nightly-2018-04-01-x86_64-apple-darwin (directory override for '/Users/user/GitHub/unrust')
rustc 1.26.0-nightly (517f24025 2018-03-31)

Is rustup show supposed to actually start installing components? I was under the impression that it was just for listing out what you have installed.

I'm on a macOS 10.12.6 host.

[kinnison]

The behaviour here comes from the fact that the default toolchain was uninstalled. Rustup forces the default toolchain to exist in many places semi-automatically. This is done to reduce surprise in a number of places, but has the side-effect of being surprising here. Perhaps we need an info: Default toolchain not installed, attempting to install... which would make it clear why it's happening?

[johnthagen]

@kinnison Personally I think a command like show should never actually install something and change the user's environment. That just seems very odd to me and I can't think of another example of a tool that does something like that.

[kinnison]

@johnthagen That's fair, I have retitled the issue and I'm happy to mentor yourself or anyone else through the process of determining why this happens, and what we can do to improve the UX and ensure it doesn't happen in future. This is nominally a breaking change in how rustup show works, but frankly I think it's right to do it.

If anyone wants help with working this one through to a PR, please comment here or find me on #wg-rustup on our Discord.

[SummerGram]

@kinnison
anyone doing this?

[kinnison]

@SummerGram I think that noone is working on this per-se. It should be fairly easy to work out what's going on after recent refactoring done by Robert.

[kellda]

What about rustup --version or rustup +toolchain --version ?

[kinnison]

I think if you explicitly say +toolchain then you're saying you want that to be installed.

[kellda]

I'm still unsure what is the right behaviour: which commands of the following should install a toolchain ?

• rustup --version
• rustup +toolchain --version
• rustup show
• rustup +toolchain show
• rustup show active-toolchain
• rustup +toolchain show active-toolchain

What about healing damaged toolchains ?

Furthermore, there are actually tests (*_not_installed in cli-rustup.rs) that check that rustup show installs the toolchain.

[kellda]

cc #1250 for the tests
cc #2252 for always installing toolchains

[kinnison]

I think, for each case we need to think about whether or not having the toolchain absent would cause confusion or breakage in scripting which may already exist and rely on behaviour. I'm prepared to introduce some breaking change so long as it's very well thought out.

In my view, if you are explicitly stating a toolchain via +toolchain or via a rust-toolchain file then we should always install that since I know some people rely on that behaviour in CI (i.e. running rustup show as part of their CI to both ensure the toolchain is present, and to display the toolchain information in the CI logs, but IIRC the projects I know doing this all have rust-toolchain files).

I also think if you're explicitly asking questions of the toolchain then it should be installed if absent (rustup show active-toolchain).

Of the examples you gave, I think that means a plain rustup --version and a plain rustup show (plain in the sense of no +toolchain and no rust-toolchain override file) are the only ones I'd entertain not force-installing the toolchain for. And they should emit a warning if the toolchain is absent.

All in all this is a somewhat confusing situation to be in, made worse because people are relying on the theoretically 'odd' behaviour.