[INFO] updating cached repository kentfredric/grease
[INFO] running `"git" "fetch" "--all"`
[INFO] [stdout] Fetching origin
[INFO] [stderr] From git://github.com/kentfredric/grease
[INFO] [stderr]  * branch            HEAD       -> FETCH_HEAD
[INFO] running `"git" "clone" "work/cache/sources/gh/kentfredric/grease" "work/ex/beta-1.38-1/sources/1.37.0/gh/kentfredric/grease"`
[INFO] [stderr] Cloning into 'work/ex/beta-1.38-1/sources/1.37.0/gh/kentfredric/grease'...
[INFO] [stderr] done.
[INFO] running `"git" "clone" "work/cache/sources/gh/kentfredric/grease" "work/ex/beta-1.38-1/sources/beta-2019-08-13/gh/kentfredric/grease"`
[INFO] [stderr] Cloning into 'work/ex/beta-1.38-1/sources/beta-2019-08-13/gh/kentfredric/grease'...
[INFO] [stderr] done.
[INFO] running `"git" "rev-parse" "HEAD"`
[INFO] [stdout] 56f6e1b303719b08166b18b40d7cfea4fe2e5c4f
[INFO] sha for GitHub repo kentfredric/grease: 56f6e1b303719b08166b18b40d7cfea4fe2e5c4f
[INFO] validating manifest of kentfredric/grease 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 kentfredric/grease 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 kentfredric/grease
[INFO] finished frobbing kentfredric/grease
[INFO] frobbed toml for kentfredric/grease written to work/ex/beta-1.38-1/sources/1.37.0/gh/kentfredric/grease/Cargo.toml
[INFO] started frobbing kentfredric/grease
[INFO] finished frobbing kentfredric/grease
[INFO] frobbed toml for kentfredric/grease written to work/ex/beta-1.38-1/sources/beta-2019-08-13/gh/kentfredric/grease/Cargo.toml
[INFO] crate kentfredric/grease already has a lockfile, it will not be regenerated
[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 kentfredric/grease against 1.37.0 for beta-1.38-1
[INFO] running `"docker" "create" "-v" "/mnt/big/crater/work/local/target-dirs/beta-1.38-1/worker-6/1.37.0:/opt/crater/target:rw,Z" "-v" "/mnt/big/crater/work/ex/beta-1.38-1/sources/1.37.0/gh/kentfredric/grease:/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" "+1.37.0" "build" "--frozen"`
[INFO] [stdout] bf7bbd71ce4060c3b400ea5719b5f3b0867d96979ffe6a756826da10d33fe8d7
[INFO] running `"docker" "start" "-a" "bf7bbd71ce4060c3b400ea5719b5f3b0867d96979ffe6a756826da10d33fe8d7"`
[INFO] [stderr]    Compiling backtrace-sys v0.1.28
[INFO] [stderr]    Compiling backtrace v0.3.26
[INFO] [stderr]    Compiling failure v0.1.5
[INFO] [stderr]    Compiling grease v0.1.0 (/opt/crater/workdir)
[INFO] [stderr] error[E0554]: #![feature] may not be used on the stable release channel
[INFO] [stderr]  --> src/lib.rs:4:39
[INFO] [stderr]   |
[INFO] [stderr] 4 | #![cfg_attr(feature = "external_doc", feature(external_doc))]
[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 `grease`.
[INFO] [stderr] 
[INFO] [stderr] To learn more, run the command again with --verbose.
[INFO] running `"docker" "inspect" "bf7bbd71ce4060c3b400ea5719b5f3b0867d96979ffe6a756826da10d33fe8d7"`
[INFO] running `"docker" "rm" "-f" "bf7bbd71ce4060c3b400ea5719b5f3b0867d96979ffe6a756826da10d33fe8d7"`
[INFO] [stdout] bf7bbd71ce4060c3b400ea5719b5f3b0867d96979ffe6a756826da10d33fe8d7