`cargo build` dumps core on latest nightly with Hello World project (macOS)

[gibfahn]

Updated to the latest nightly earlier today, and immediately started noticing a marked compile time slowdown in cargo build (debug mode) for small projects.

EDIT: Turns out the slowdown is because it's dumping a core to /cores, I worked this out when my machine became completely full 😁 .

Platform: macOS High Sierra.

NOTE (added by @pnkfelix): it appears you need to turn up a core dump threshold to observe this, e.g. via ulimit -c unlimited

$ rustup update                                                                                                                                                                                         ~/tmp
info: syncing channel updates for 'stable-x86_64-apple-darwin'
info: syncing channel updates for 'nightly-x86_64-apple-darwin'
info: checking for self-updates

   stable-x86_64-apple-darwin unchanged - rustc 1.22.1 (05e2e1c41 2017-11-22)
  nightly-x86_64-apple-darwin unchanged - rustc 1.24.0-nightly (1956d5535 2017-12-03)

$ cargo new --bin hello_nightly && cd hello_nightly                                                                                                                                                 ~/tmp
     Created binary (application) `hello_nightly` project

$ time rustup run nightly cargo build                                                                                                                                       ~/tmp/hello_nightly (master*)
   Compiling hello_nightly v0.1.0 (file:///Users/gib/tmp/hello_nightly)
    Finished dev [unoptimized + debuginfo] target(s) in 3.0 secs
rustup run nightly cargo build  0.32s user 1.17s system 46% cpu 3.229 total

$ touch src/main.rs && time rustup run nightly cargo build                                                                                                               ~/tmp/hello_nightly 3s (master*)
   Compiling hello_nightly v0.1.0 (file:///Users/gib/tmp/hello_nightly)
    Finished dev [unoptimized + debuginfo] target(s) in 2.90 secs
rustup run nightly cargo build  0.33s user 1.07s system 44% cpu 3.133 total

$ cd ..                                                                                                                                                                  ~/tmp/hello_nightly 3s (master*)

$ cargo new --bin hello_stable && cd hello_stable                                                                                                                                                   ~/tmp
     Created binary (application) `hello_stable` project

$ time rustup run stable cargo build                                                                                                                                         ~/tmp/hello_stable (master*)
   Compiling hello_stable v0.1.0 (file:///Users/gib/tmp/hello_stable)
    Finished dev [unoptimized + debuginfo] target(s) in 0.53 secs
rustup run stable cargo build  0.37s user 0.23s system 65% cpu 0.908 total

$ touch src/main.rs && time rustup run stable cargo build                                                                                                                 ~/tmp/hello_stable 1s (master*)
   Compiling hello_stable v0.1.0 (file:///Users/gib/tmp/hello_stable)
    Finished dev [unoptimized + debuginfo] target(s) in 0.31 secs
rustup run stable cargo build  0.33s user 0.17s system 92% cpu 0.542 total

Sorry if this is a duplicate, didn't see anything relevant in the issue tracker.

[gibfahn]

Doesn't seem to happen with cargo build --release:

$ touch src/main.rs && time rustup run stable cargo build --release                                                                                                      ~/tmp/hello_nightly 1s (master*)
   Compiling hello_nightly v0.1.0 (file:///Users/gib/tmp/hello_nightly)
    Finished release [optimized] target(s) in 0.25 secs
rustup run stable cargo build --release  0.29s user 0.15s system 93% cpu 0.478 total
$ touch src/main.rs && time rustup run nightly cargo build --release                                                                                                        ~/tmp/hello_nightly (master*)
   Compiling hello_nightly v0.1.0 (file:///Users/gib/tmp/hello_nightly)
    Finished release [optimized] target(s) in 0.25 secs
rustup run nightly cargo build --release  0.29s user 0.16s system 93% cpu 0.482 total

[nikomatsakis]

@gibfahn I'm a bit confused. If I'm not misreading things, it appears that the nightly build is faster (at least in the one case where the numbers are not identical):

rustup run nightly cargo build 0.32s user 1.17s system 46% cpu 3.229 total

vs

rustup run stable cargo build 0.37s user 0.23s system 65% cpu 0.908 total

[nikomatsakis]

No, nm, I was getting confused by time output. I see... 3.229 total vs 0.908 total. =)

[gibfahn]

Still happens with the newest nightly (rustc 1.24.0-nightly (5a2465e2b 2017-12-06)). Reproduced on someone else's laptop as well (also macOS).

Pretty easy to reproduce:

# Get rust if you haven't already
curl https://sh.rustup.rs -sSf | sh
rustup install nightly

cargo new --bin rust-foo && cd rust-foo
cargo build
touch src/main.rs && time cargo +stable build
touch src/main.rs && time cargo +nightly build
cd .. && rm -rf rust-foo

EDIT: Can't reproduce this on Ubuntu

[nikomatsakis]

@gibfahn just to be clear, if you diff those two projects, do you see any difference? i.e., it seems to me you should be able to just have one project and do cargo +nightly build and compare to cargo +stable build... can you check that?

[nikomatsakis]

I don't see any significant difference on linux, anyway.

[gibfahn]

@nikomatsakis are you running on macOS? I'll keep a list of platforms I tried it on.

Using the shortened script above I reproduced with the same code.

Platform	Fast (💚 ) / Slow (🔴 )
macOS High Sierra 10.13.1	🔴
macOS Sierra	🔴
Ubuntu 16.04	💚
Rhel 7.4	💚

$ cargo new --bin rust-foo && cd rust-foo
     Created binary (application) `rust-foo` project
Cargo.toml src

$ cargo build
   Compiling rust-foo v0.1.0 (file:///Users/gib/tmp/rust-foo)
    Finished dev [unoptimized + debuginfo] target(s) in 2.92 secs

$ touch src/main.rs && time cargo +stable build
   Compiling rust-foo v0.1.0 (file:///Users/gib/tmp/rust-foo)
    Finished dev [unoptimized + debuginfo] target(s) in 0.39 secs
cargo +stable build  0.37s user 0.22s system 92% cpu 0.639 total

$ touch src/main.rs && time cargo +nightly build
   Compiling rust-foo v0.1.0 (file:///Users/gib/tmp/rust-foo)
    Finished dev [unoptimized + debuginfo] target(s) in 2.74 secs
cargo +nightly build  0.34s user 1.06s system 47% cpu 2.995 total

[Mark-Simulacrum]

I cannot reproduce on macOS High Sierra 10.13.2.

[gibfahn]

I cannot reproduce on macOS High Sierra 10.13.2.

Odd, not sure what the difference could be.

In case it's a hardware thing, this is my machine's configuration:

[Mark-Simulacrum]

It might be helpful to have a bash script that'll run the commands for me just in case, but as far as I can tell I have the same make of hardware, just a slightly different version of macOS. Seems unlikely that would be the culprit, though...

[gibfahn]

@Mark-Simulacrum the script in #46505 (comment) is exactly what I'm doing.

I tried this on a different machine (same OS level, different hardware configuration) and it didn't have the same problem. I'm not sure how else to debug.

[Mark-Simulacrum]

Clearing out ~/.cargo or at least make sure both machines have the same content might help.

[gibfahn]

Did an uninstall and reinstall (rustup self uninstall), and I can no longer reproduce:

$ cargo new --bin rust-foo && cd rust-foo
     Created binary (application) `rust-foo` project
$ cargo build
   Compiling rust-foo v0.1.0 (file:///Users/gib/tmp/rust-foo)
    Finished dev [unoptimized + debuginfo] target(s) in 0.92 secs
$ touch src/main.rs && time cargo +stable build
   Compiling rust-foo v0.1.0 (file:///Users/gib/tmp/rust-foo)
    Finished dev [unoptimized + debuginfo] target(s) in 0.31 secs
cargo +stable build  0.26s user 0.17s system 92% cpu 0.466 total
$ touch src/main.rs && time cargo +nightly build
   Compiling rust-foo v0.1.0 (file:///Users/gib/tmp/rust-foo)
    Finished dev [unoptimized + debuginfo] target(s) in 0.57 secs
cargo +nightly build  0.31s user 0.22s system 68% cpu 0.774 total

I did have a fair amount of stuff in $CARGO_HOME, so I guess something in there must have affected it:

▶▶▶ ls *                                                                                                                                                                             ~/.local/share/cargo
env

bin:
cargo             cargo-fmt         cargo-watch       cobalt            ion               racer             rust-gdb          rustc             rustfmt           s                 xi-syntect-plugin
cargo-clippy      cargo-wa          clippy-driver     exa               pijul             rls               rust-lldb         rustdoc           rustup            xi-core

git:
checkouts db

registry:
cache index src

Thanks for troubleshooting!