Pretty-print mode to replace glob imports with a precise list of names

[bstrie]

13:58 < bstrie> is there a pretty-print mode to replace a glob import with a
                precise list of names?
13:59 <@pcwalton> bstrie: no unfortunately
13:59 <@pcwalton> good idea though

So if I have a file with this:

use foo::*;

...and of all the things that foo provides, I only ever end up using bar and baz, then it should rewrite the import to:

use foo::{bar, baz};

[catamorphism]

Added far-future milestone

[bblum]

Ooh, this would be great.

[huonw]

Triage: no change. Globs are now behind a #[feature] so this is probably slightly lower priority.

[pnkfelix]

@huonw or maybe the feature guard makes this higher priority, since it would ease development shifting from local-hacking-mode that uses feature guards and relase-to-the-wild mode that tries to eschew feature guards. :)

[sanxiyn]

cc @nick29581 who hinted at "a deglobber tool which would convert glob imports to proper imports" in #19254.

[nrc]

FTR, save-analysis now knows exactly the list of imports needed for this (since #19254), so all that is needed is to use that info in pretty printing.

I was actually thinking of making this an external tool, possibly a Cargo plugin. I've been playing around with an approach to this, but haven't got very far. If anyone wants to work on this, please ping me.

[steveklabnik]

I'm pulling a massive triage effort to get us ready for 1.0. As part of this, I'm moving stuff that's wishlist-like to the RFCs repo, as that's where major new things should get discussed/prioritized.

This issue has been moved to the RFCs repo: rust-lang/rfcs#617