[INFO] crate mech-program 0.0.2 is already in cache
[INFO] extracting crate mech-program 0.0.2 into work/ex/beta-1.38-1/sources/1.37.0/reg/mech-program/0.0.2
[INFO] extracting crate mech-program 0.0.2 into work/ex/beta-1.38-1/sources/beta-2019-08-13/reg/mech-program/0.0.2
[INFO] validating manifest of mech-program-0.0.2 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 mech-program-0.0.2 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 mech-program-0.0.2
[INFO] finished frobbing mech-program-0.0.2
[INFO] frobbed toml for mech-program-0.0.2 written to work/ex/beta-1.38-1/sources/1.37.0/reg/mech-program/0.0.2/Cargo.toml
[INFO] started frobbing mech-program-0.0.2
[INFO] finished frobbing mech-program-0.0.2
[INFO] frobbed toml for mech-program-0.0.2 written to work/ex/beta-1.38-1/sources/beta-2019-08-13/reg/mech-program/0.0.2/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] [stderr]     Blocking waiting for file lock on package cache
[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] [stderr]     Blocking waiting for file lock on package cache
[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] [stderr]     Blocking waiting for file lock on package cache
[INFO] testing mech-program-0.0.2 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-6/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/mech-program/0.0.2:/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] 2954e998ed441b58e7f47544f95c6ad52149a8a424cf5590191dde37a79a502e
[INFO] running `"docker" "start" "-a" "2954e998ed441b58e7f47544f95c6ad52149a8a424cf5590191dde37a79a502e"`
[INFO] [stderr]    Compiling serde v1.0.99
[INFO] [stderr]    Compiling hashbrown v0.4.0
[INFO] [stderr]    Compiling num-iter v0.1.39
[INFO] [stderr]    Compiling num-rational v0.2.2
[INFO] [stderr] error[E0554]: `#![feature]` may not be used on the beta release channel
[INFO] [stderr]   --> /opt/crater/cargo-home/registry/src/github.com-1ecc6299db9ec823/hashbrown-0.4.0/src/lib.rs:15:5
[INFO] [stderr]    |
[INFO] [stderr] 15 | /     feature(
[INFO] [stderr] 16 | |         alloc_layout_extra,
[INFO] [stderr] 17 | |         allocator_api,
[INFO] [stderr] 18 | |         ptr_offset_from,
[INFO] [stderr] ...  |
[INFO] [stderr] 21 | |         dropck_eyepatch
[INFO] [stderr] 22 | |     )
[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 `hashbrown`.
[INFO] [stderr] warning: build failed, waiting for other jobs to finish...
[INFO] [stderr] error: build failed
[INFO] running `"docker" "inspect" "2954e998ed441b58e7f47544f95c6ad52149a8a424cf5590191dde37a79a502e"`
[INFO] running `"docker" "rm" "-f" "2954e998ed441b58e7f47544f95c6ad52149a8a424cf5590191dde37a79a502e"`
[INFO] [stdout] 2954e998ed441b58e7f47544f95c6ad52149a8a424cf5590191dde37a79a502e