[INFO] crate mwmatching 0.1.1 is already in cache
[INFO] extracting crate mwmatching 0.1.1 into work/ex/beta-1.38-1/sources/1.37.0/reg/mwmatching/0.1.1
[INFO] extracting crate mwmatching 0.1.1 into work/ex/beta-1.38-1/sources/beta-2019-08-13/reg/mwmatching/0.1.1
[INFO] validating manifest of mwmatching-0.1.1 on toolchain 1.37.0
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+1.37.0" "read-manifest" "--manifest-path" "Cargo.toml"`
[INFO] validating manifest of mwmatching-0.1.1 on toolchain beta-2019-08-13
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+beta-2019-08-13" "read-manifest" "--manifest-path" "Cargo.toml"`
[INFO] started frobbing mwmatching-0.1.1
[INFO] finished frobbing mwmatching-0.1.1
[INFO] frobbed toml for mwmatching-0.1.1 written to work/ex/beta-1.38-1/sources/1.37.0/reg/mwmatching/0.1.1/Cargo.toml
[INFO] started frobbing mwmatching-0.1.1
[INFO] finished frobbing mwmatching-0.1.1
[INFO] frobbed toml for mwmatching-0.1.1 written to work/ex/beta-1.38-1/sources/beta-2019-08-13/reg/mwmatching/0.1.1/Cargo.toml
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+1.37.0" "generate-lockfile" "--manifest-path" "Cargo.toml" "-Zno-index-update"`
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+beta-2019-08-13" "generate-lockfile" "--manifest-path" "Cargo.toml" "-Zno-index-update"`
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+1.37.0" "fetch" "--locked" "--manifest-path" "Cargo.toml"`
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+beta-2019-08-13" "fetch" "--locked" "--manifest-path" "Cargo.toml"`
[INFO] testing mwmatching-0.1.1 against beta-2019-08-13 for beta-1.38-1
[INFO] running `"docker" "create" "-v" "/mnt/big/crater/work/local/target-dirs/beta-1.38-1/worker-7/beta-2019-08-13:/opt/crater/target:rw,Z" "-v" "/mnt/big/crater/work/ex/beta-1.38-1/sources/beta-2019-08-13/reg/mwmatching/0.1.1:/opt/crater/workdir:ro,Z" "-v" "/mnt/big/crater/work/local/cargo-home:/opt/crater/cargo-home:ro,Z" "-v" "/mnt/big/crater/work/local/rustup-home:/opt/crater/rustup-home:ro,Z" "-e" "USER_ID=1000" "-e" "SOURCE_DIR=/opt/crater/workdir" "-e" "MAP_USER_ID=1000" "-e" "CARGO_TARGET_DIR=/opt/crater/target" "-e" "CARGO_INCREMENTAL=0" "-e" "RUST_BACKTRACE=full" "-e" "RUSTFLAGS=--cap-lints=warn" "-e" "CARGO_HOME=/opt/crater/cargo-home" "-e" "RUSTUP_HOME=/opt/crater/rustup-home" "-w" "/opt/crater/workdir" "-m" "1536M" "--network" "none" "rustops/crates-build-env" "/opt/crater/cargo-home/bin/cargo" "+beta-2019-08-13" "build" "--frozen"`
[INFO] [stdout] 4cc4b9b5ed5a4635f9b100427b859410081ebbd55a10033f73c49a7d5474d531
[INFO] running `"docker" "start" "-a" "4cc4b9b5ed5a4635f9b100427b859410081ebbd55a10033f73c49a7d5474d531"`
[INFO] [stderr]    Compiling mwmatching v0.1.1 (/opt/crater/workdir)
[INFO] [stderr] warning: variable does not need to be mutable
[INFO] [stderr]    --> src/lib.rs:744:25
[INFO] [stderr]     |
[INFO] [stderr] 744 |                     let mut k = p / 2;
[INFO] [stderr]     |                         ----^
[INFO] [stderr]     |                         |
[INFO] [stderr]     |                         help: remove this `mut`
[INFO] [stderr]     |
[INFO] [stderr]     = note: `#[warn(unused_mut)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: variable does not need to be mutable
[INFO] [stderr]    --> src/lib.rs:852:29
[INFO] [stderr]     |
[INFO] [stderr] 852 |                         let mut k = p / 2;
[INFO] [stderr]     |                             ----^
[INFO] [stderr]     |                             |
[INFO] [stderr]     |                             help: remove this `mut`
[INFO] [stderr] 
[INFO] [stderr]     Finished dev [unoptimized + debuginfo] target(s) in 0.99s
[INFO] running `"docker" "inspect" "4cc4b9b5ed5a4635f9b100427b859410081ebbd55a10033f73c49a7d5474d531"`
[INFO] running `"docker" "rm" "-f" "4cc4b9b5ed5a4635f9b100427b859410081ebbd55a10033f73c49a7d5474d531"`
[INFO] [stdout] 4cc4b9b5ed5a4635f9b100427b859410081ebbd55a10033f73c49a7d5474d531
[INFO] running `"docker" "create" "-v" "/mnt/big/crater/work/local/target-dirs/beta-1.38-1/worker-7/beta-2019-08-13:/opt/crater/target:rw,Z" "-v" "/mnt/big/crater/work/ex/beta-1.38-1/sources/beta-2019-08-13/reg/mwmatching/0.1.1:/opt/crater/workdir:ro,Z" "-v" "/mnt/big/crater/work/local/cargo-home:/opt/crater/cargo-home:ro,Z" "-v" "/mnt/big/crater/work/local/rustup-home:/opt/crater/rustup-home:ro,Z" "-e" "USER_ID=1000" "-e" "SOURCE_DIR=/opt/crater/workdir" "-e" "MAP_USER_ID=1000" "-e" "CARGO_TARGET_DIR=/opt/crater/target" "-e" "CARGO_INCREMENTAL=0" "-e" "RUST_BACKTRACE=full" "-e" "RUSTFLAGS=--cap-lints=warn" "-e" "CARGO_HOME=/opt/crater/cargo-home" "-e" "RUSTUP_HOME=/opt/crater/rustup-home" "-w" "/opt/crater/workdir" "-m" "1536M" "--network" "none" "rustops/crates-build-env" "/opt/crater/cargo-home/bin/cargo" "+beta-2019-08-13" "test" "--frozen" "--no-run"`
[INFO] [stdout] 38f5db786f9f1f9a9139bcf46b25ca37109fe26485215f67e0fc94ab039010b9
[INFO] running `"docker" "start" "-a" "38f5db786f9f1f9a9139bcf46b25ca37109fe26485215f67e0fc94ab039010b9"`
[INFO] [stderr]    Compiling mwmatching v0.1.1 (/opt/crater/workdir)
[INFO] [stderr] error[E0554]: `#![feature]` may not be used on the beta release channel
[INFO] [stderr]  --> examples/largedata/main.rs:1:1
[INFO] [stderr]   |
[INFO] [stderr] 1 | #![feature(rustc_private)]
[INFO] [stderr]   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] error: aborting due to previous error
[INFO] [stderr] 
[INFO] [stderr] For more information about this error, try `rustc --explain E0554`.
[INFO] [stderr] error: Could not compile `mwmatching`.
[INFO] [stderr] warning: build failed, waiting for other jobs to finish...
[INFO] [stderr] warning: variable does not need to be mutable
[INFO] [stderr]    --> src/lib.rs:744:25
[INFO] [stderr]     |
[INFO] [stderr] 744 |                     let mut k = p / 2;
[INFO] [stderr]     |                         ----^
[INFO] [stderr]     |                         |
[INFO] [stderr]     |                         help: remove this `mut`
[INFO] [stderr]     |
[INFO] [stderr]     = note: `#[warn(unused_mut)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: variable does not need to be mutable
[INFO] [stderr]    --> src/lib.rs:852:29
[INFO] [stderr]     |
[INFO] [stderr] 852 |                         let mut k = p / 2;
[INFO] [stderr]     |                             ----^
[INFO] [stderr]     |                             |
[INFO] [stderr]     |                             help: remove this `mut`
[INFO] [stderr] 
[INFO] [stderr] error: build failed
[INFO] running `"docker" "inspect" "38f5db786f9f1f9a9139bcf46b25ca37109fe26485215f67e0fc94ab039010b9"`
[INFO] running `"docker" "rm" "-f" "38f5db786f9f1f9a9139bcf46b25ca37109fe26485215f67e0fc94ab039010b9"`
[INFO] [stdout] 38f5db786f9f1f9a9139bcf46b25ca37109fe26485215f67e0fc94ab039010b9