[INFO] fetching crate un_algebra 0.9.0...
[INFO] testing un_algebra-0.9.0 against 1.49.0 for beta-1.50-1
[INFO] extracting crate un_algebra 0.9.0 into /workspace/builds/worker-13/source
[INFO] validating manifest of crates.io crate un_algebra 0.9.0 on toolchain 1.49.0
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+1.49.0" "read-manifest" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] started tweaking crates.io crate un_algebra 0.9.0
[INFO] finished tweaking crates.io crate un_algebra 0.9.0
[INFO] tweaked toml for crates.io crate un_algebra 0.9.0 written to /workspace/builds/worker-13/source/Cargo.toml
[INFO] crate crates.io crate un_algebra 0.9.0 already has a lockfile, it will not be regenerated
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+1.49.0" "fetch" "--locked" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]  Downloading crates ...
[INFO] [stderr]   Downloaded bit-set v0.5.1
[INFO] [stderr]   Downloaded rusty-fork v0.2.2
[INFO] [stderr]   Downloaded num-bigint v0.2.3
[INFO] [stderr]   Downloaded num-traits v0.2.10
[INFO] [stderr]   Downloaded proptest-derive v0.1.2
[INFO] [stderr]   Downloaded proptest v0.9.4
[INFO] [stderr]   Downloaded bit-vec v0.5.1
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-13/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-13/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "rustops/crates-build-env@sha256:b8eeb62f26c39b23691079a6cb6de528d8e88b4d71a8f6b1d30f8ba7d9c16de9" "/opt/rustwide/cargo-home/bin/cargo" "+1.49.0" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stdout] 7f617d811c6d077dc539a004ccae12ed6ee57678d92f5188dc60b83ea2a54875
[INFO] [stderr] WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
[INFO] running `Command { std: "docker" "start" "-a" "7f617d811c6d077dc539a004ccae12ed6ee57678d92f5188dc60b83ea2a54875", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "7f617d811c6d077dc539a004ccae12ed6ee57678d92f5188dc60b83ea2a54875", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "7f617d811c6d077dc539a004ccae12ed6ee57678d92f5188dc60b83ea2a54875", kill_on_drop: false }`
[INFO] [stdout] 7f617d811c6d077dc539a004ccae12ed6ee57678d92f5188dc60b83ea2a54875
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-13/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-13/source:/opt/rustwide/workdir:ro,Z" "-v" "/var/lib/crater-agent-workspace/cargo-home:/opt/rustwide/cargo-home:ro,Z" "-v" "/var/lib/crater-agent-workspace/rustup-home:/opt/rustwide/rustup-home:ro,Z" "-e" "SOURCE_DIR=/opt/rustwide/workdir" "-e" "CARGO_TARGET_DIR=/opt/rustwide/target" "-e" "CARGO_INCREMENTAL=0" "-e" "RUST_BACKTRACE=full" "-e" "RUSTFLAGS=--cap-lints=warn" "-e" "CARGO_HOME=/opt/rustwide/cargo-home" "-e" "RUSTUP_HOME=/opt/rustwide/rustup-home" "-w" "/opt/rustwide/workdir" "-m" "1610612736" "--user" "0:0" "--network" "none" "rustops/crates-build-env@sha256:b8eeb62f26c39b23691079a6cb6de528d8e88b4d71a8f6b1d30f8ba7d9c16de9" "/opt/rustwide/cargo-home/bin/cargo" "+1.49.0" "build" "--frozen" "--message-format=json", kill_on_drop: false }`
[INFO] [stderr] WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
[INFO] [stdout] 932c9a83918be99a6c37a8ed2a8d139d40b60221102d19df3f4c7dd59c6545db
[INFO] running `Command { std: "docker" "start" "-a" "932c9a83918be99a6c37a8ed2a8d139d40b60221102d19df3f4c7dd59c6545db", kill_on_drop: false }`
[INFO] [stderr]    Compiling syn v0.15.44
[INFO] [stderr]    Compiling byteorder v1.3.2
[INFO] [stderr]    Compiling bit-vec v0.5.1
[INFO] [stderr]    Compiling regex-syntax v0.6.12
[INFO] [stderr]    Compiling num-traits v0.2.10
[INFO] [stderr]    Compiling wait-timeout v0.2.0
[INFO] [stderr]    Compiling rand v0.6.5
[INFO] [stderr]    Compiling rusty-fork v0.2.2
[INFO] [stderr]    Compiling bit-set v0.5.1
[INFO] [stderr]    Compiling num-integer v0.1.41
[INFO] [stderr]    Compiling num-complex v0.2.3
[INFO] [stderr]    Compiling num-bigint v0.2.3
[INFO] [stderr]    Compiling num-iter v0.1.39
[INFO] [stderr]    Compiling proptest v0.9.4
[INFO] [stderr]    Compiling num-rational v0.2.2
[INFO] [stderr]    Compiling num v0.2.0
[INFO] [stderr]    Compiling proptest-derive v0.1.2
[INFO] [stderr]    Compiling un_algebra v0.9.0 (/opt/rustwide/workdir)
[INFO] [stdout] error[E0554]: `#![feature]` may not be used on the stable release channel
[INFO] [stdout]  --> src/lib.rs:1:1
[INFO] [stdout]   |
[INFO] [stdout] 1 | #![feature(external_doc)]
[INFO] [stdout]   | ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] error: aborting due to previous error
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] For more information about this error, try `rustc --explain E0554`.
[INFO] [stdout] 
[INFO] [stderr] error: could not compile `un_algebra`
[INFO] [stderr] 
[INFO] [stderr] To learn more, run the command again with --verbose.
[INFO] running `Command { std: "docker" "inspect" "932c9a83918be99a6c37a8ed2a8d139d40b60221102d19df3f4c7dd59c6545db", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "932c9a83918be99a6c37a8ed2a8d139d40b60221102d19df3f4c7dd59c6545db", kill_on_drop: false }`
[INFO] [stdout] 932c9a83918be99a6c37a8ed2a8d139d40b60221102d19df3f4c7dd59c6545db