Help us benchmark incremental compilation!

29 
$ cargo --version
cargo 0.24.0-nightly (859c2305b 2017-10-29)
$ rustc --version
rustc 1.23.0-nightly (2be4cc040 2017-11-01)

bindgen

Fresh release build

$ rm -rf target/
$ time cargo +nightly build --release
<snip>
    Finished release [optimized] target(s) in 168.22 secs

real	2m48.579s
user	4m33.232s
sys	0m3.316s

Fresh incremental+release build

$ rm -rf target/
$ CARGO_INCREMENTAL=1 time cargo +nightly build --release
<snip>
    Finished release [optimized] target(s) in 44.76 secs

real	0m45.112s
user	4m41.256s
sys	0m3.988s

touch src/lib.rs and incremental rebuild

$ touch src/lib.rs
$ time cargo +nightly build --release
   Compiling bindgen v0.31.3 (file:///home/fitzgen/rust-bindgen)
    Finished release [optimized] target(s) in 8.29 secs

real	0m8.639s
user	0m8.220s
sys	0m0.504s

Add a public no-op method and incremental rebuild

$ time cargo +nightly build --release
   Compiling bindgen v0.31.3 (file:///home/fitzgen/rust-bindgen)
    Finished release [optimized] target(s) in 9.47 secs

real	0m9.820s
user	0m11.708s
sys	0m0.564s

Really impressed and surprised that fresh incremental builds are so much faster than fresh non-incremental builds!