option to install toolchain version IFF it has certain components

[matthiaskrgr]

When dealing with continuous like travis, I can specify a toolchain I want to have

language: rust
rust:
  - beta
  - nightly

but not what components (rustfmt clippy) I want to install.
This means if I want to use clippy or rustfmt, I have to manually rustup component add it or, if the current nightly version does not ship it, try to somehow install it myself and hope it builds with the current rustc nightly.
It would be great to have some kind of option "install the lastest nightly that has components x and y available" which entails potentially downgrading to a earlier nightly if the current nightly does not ship the components but the later nightly does.

Perhaps rustup install nightly --needed-components=clippy,rustfmt or something like that.

[RalfJung]

The title of this issue is misleading... it talks about updating when the issue is about installation.

Could someone rename it appropriately? I think this is the better alternative to #1602 and #1676.

[matthiaskrgr]

@RalfJung updated!

[najamelan]

@RalfJung

it talks about updating when the issue is about installation

It would be nice if rustup update did the same thing though. Eg. get you the latest nightly that has your components.

[RalfJung]

@najamelan your comment consists only of quotes, looks like a formatting issue?

get you the latest nightly that has your components.

AFAIK if you have a component installed, rustup will only upgrade to nighties that have that component.

[najamelan]

@RalfJung Sorry, it needed a white line to work there.

AFAIK if you have a component installed, rustup will only upgrade to nighties that have that component.

So the point is, if I have a nightly that is one month old, with components, and I run rustup update, if todays nightly doesn't have the components, it won't update anything at all, even if yesterdays nightly had the required components.

So I think lots of people would like for rustup to update to the latest nightly that has that component.

The issue is very similar for installs and updates, so I think both should considered together when trying to solve this.