Cargo spends most of 'cargo build' time writing to output on Windows

[LPGhatguy]

Problem
I have a Rust project with around 250 total dependencies. It's pretty cool, you can see it here: https://github.com/LPGhatguy/rojo

When I run cargo build with no code changes after a complete build, Cargo takes around 2600ms. When I redirect stderr to /dev/null or pass the -q flag, that time drops to around 490ms.

Time with output showing in console:

$ time cargo build
    Finished dev [unoptimized + debuginfo] target(s) in 2.46s

real    0m2.559s
user    0m0.000s
sys     0m0.015s

$ time cargo build
    Finished dev [unoptimized + debuginfo] target(s) in 2.51s

real    0m2.603s
user    0m0.015s
sys     0m0.000s

Time redirecting stderr to /dev/null:

$ time cargo build 2>/dev/null

real    0m0.493s
user    0m0.000s
sys     0m0.015s

$ time cargo build 2>/dev/null

real    0m0.490s
user    0m0.000s
sys     0m0.030s

Steps

1. Be on Windows
2. Compile a Rust project via cargo build via cmd.exe
3. Weep

Possible Solution(s)

cargo build -p and cargo build 2>/dev/null both suppress the progress bar output and fix the problem, but I like the progress bar because it's pretty and helpful.

Windows' terminal emulator, ConHost, has very very slow writes. I have lots of crates!

Notes
Windows 10, build 1809, using Git Bash or cmd.exe, which both use ConHost.

Output of cargo version:

$ cargo version
cargo 1.32.0 (8610973aa 2019-01-02)

[ehuss]

Thanks for the report. I think this may be fixed (or at least better) on the latest nightly. Can you try with nightly and see how it goes? I think it needs to be a a nightly after 2019-02-06.

[LPGhatguy]

@ehuss Looks great on nightly! Thanks for the tip!

$ time cargo +nightly build
    Finished dev [unoptimized + debuginfo] target(s) in 0.38s

real    0m0.481s
user    0m0.000s
sys     0m0.015s

$ time cargo +nightly build 2>/dev/null

real    0m0.468s
user    0m0.000s
sys     0m0.015s