Display progress when compiling dependencies

[rphmeier]

e.g.

[1 / n] Compiling foo v0.0.1
[2 / n] Compiling bar v0.3.5
...

When compiling a crate with a lot of transitive dependencies (which themselves may not be trivial), it would be nice to see about how many crates are left to compile.

[srinivasreddy]

When we compile with concurrent jobs don't we get the order jumbled?

[rphmeier]

An atomic counter could be used to keep a consistent order between threads. I will look into implementing this later today.

[alexcrichton]

cc rust-lang/rust#24335, specifically rust-lang/rust#24335 (comment).

I'm somewhat wary of doing this because of:

• There's still no indication what's actually running
• There's not necessarily a sense of overall progress as it's just the number of rustc commands we're issuing.
• Calculating how much needs to run may actually be nontrivial in Cargo itself

But that being said, I'd love to see progress here! Ideally we could get some form of hooks into the compiler indicating where it is and we could provide an interactive UI which indicates the progress of compilation (even concurrently), but that may be kinda difficult to implement :(

[nox]

Wasn't this implemented with them fancy progress bars?

[mbrubeck]

This was implemented by #5620, disabled by #5698, and re-introduced behind the unstable -Zcompile-progress option in #5716.