crash while downloading sources on osx: index out of bounds: the len is 2 but the index is 2 in cpu.rs

[matthiaskrgr]

I saw this on travis ci where cargo crashed while downloading sources https://travis-ci.org/matthiaskrgr/cargo-cache/jobs/589269657#L176

  Downloaded smallvec v0.6.10
  Downloaded nodrop v0.1.13
  Downloaded rustc_version v0.2.3
thread 'main' panicked at 'index out of bounds: the len is 2 but the index is 2', src/tools/cargo/src/cargo/util/cpu.rs:152:29
stack backtrace:
   0:        0x1067261c5 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h5e40db06808a02c5
   1:        0x1067502c0 - core::fmt::write::he42958ab73416f43
   2:        0x10671e95b - std::io::Write::write_fmt::h60fdb55d3cacc277
   3:        0x10672989a - std::panicking::default_hook::{{closure}}::h9780f2f769b47a1f
   4:        0x1067295a5 - std::panicking::default_hook::h0208c7cfccea4189
   5:        0x106729ff7 - std::panicking::rust_panic_with_hook::h6c68a3aa4cc51ab7
   6:        0x106729b3d - std::panicking::continue_panic_fmt::h667797a1c6f98cf4
   7:        0x106729a39 - rust_begin_unwind
   8:        0x10674c71f - core::panicking::panic_fmt::ha61f731b713c1136
   9:        0x10674c6d9 - core::panicking::panic_bounds_check::h59db8045e71cfa5b
  10:        0x106293c20 - cargo::util::cpu::imp::current::hb13374f4fa25be14
  11:        0x10626c478 - cargo::core::compiler::job_queue::JobQueue::new::ha5e8b69e006e7f20
  12:        0x10601c444 - cargo::core::compiler::context::Context::compile::h25c90854c2d82f04
  13:        0x10602e990 - cargo::ops::cargo_compile::compile_ws::h99547f1cd1d02754
  14:        0x106029838 - cargo::ops::cargo_compile::compile::h9ddab4fe76991076
  15:        0x105eba626 - cargo::commands::build::exec::ha76e54e95dc52e83
  16:        0x105ec5c6d - cargo::cli::main::hea6e36614a3e7f7f
  17:        0x105f11ddd - cargo::main::ha002fee9b72cb617
  18:        0x105eedb16 - std::rt::lang_start::{{closure}}::h0f2d5194c8bc3f40
  19:        0x1067299b8 - std::panicking::try::do_call::h08253a98d0a78550
  20:        0x10673429f - __rust_maybe_catch_panic
  21:        0x10672a45e - std::rt::lang_start_internal::h7259a5fe6e7e4a74
  22:        0x105f14469 - main
The command "cargo build --all ${RELEASE}" exited with 101.

cargo 1.39.0-nightly (b6c6f685b 2019-09-19)

[jonas-schievink]

Haha, this will panic on any system with <4 processors

cargo/src/cargo/util/cpu.rs

Lines 149 to 154 in 400221e

	for chunk in cpu_info.chunks(num_cpus_u as usize) {
	ret.user += chunk[CPU_STATE_USER] as u64;
	ret.system += chunk[CPU_STATE_SYSTEM] as u64;
	ret.idle += chunk[CPU_STATE_IDLE] as u64;
	ret.nice += chunk[CPU_STATE_NICE] as u64;
	}