[INFO] fetching crate letsgo 0.0.1...
[INFO] documenting letsgo-0.0.1 against beta-2020-08-29 for beta-1.47-rustdoc-1
[INFO] extracting crate letsgo 0.0.1 into /workspace/builds/worker-2/source
[INFO] validating manifest of crates.io crate letsgo 0.0.1 on toolchain beta-2020-08-29
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+beta-2020-08-29" "read-manifest" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] started tweaking crates.io crate letsgo 0.0.1
[INFO] finished tweaking crates.io crate letsgo 0.0.1
[INFO] tweaked toml for crates.io crate letsgo 0.0.1 written to /workspace/builds/worker-2/source/Cargo.toml
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+beta-2020-08-29" "generate-lockfile" "--manifest-path" "Cargo.toml" "-Zno-index-update", kill_on_drop: false }`
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+beta-2020-08-29" "fetch" "--locked" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]  Downloading crates ...
[INFO] [stderr]   Downloaded async-ready v3.0.0
[INFO] [stderr]   Downloaded romio v0.3.0-alpha.10
[INFO] [stderr]   Downloaded async-datagram v3.0.0
[INFO] [stderr]   Downloaded runtime-tokio v0.3.0-alpha.6
[INFO] [stderr]   Downloaded futures-preview v0.3.0-alpha.18
[INFO] [stderr]   Downloaded futures-io-preview v0.3.0-alpha.18
[INFO] [stderr]   Downloaded runtime v0.3.0-alpha.7
[INFO] [stderr]   Downloaded futures-executor-preview v0.3.0-alpha.18
[INFO] [stderr]   Downloaded futures-sink-preview v0.3.0-alpha.18
[INFO] [stderr]   Downloaded futures-util-preview v0.3.0-alpha.18
[INFO] [stderr]   Downloaded futures-core-preview v0.3.0-alpha.18
[INFO] [stderr]   Downloaded runtime-native v0.3.0-alpha.6
[INFO] [stderr]   Downloaded futures-channel-preview v0.3.0-alpha.18
[INFO] [stderr]   Downloaded futures-select-macro-preview v0.3.0-alpha.18
[INFO] [stderr]   Downloaded runtime-raw v0.3.0-alpha.5
[INFO] [stderr]   Downloaded runtime-attributes v0.3.0-alpha.6
[INFO] [stderr]   Downloaded juliex v0.3.0-alpha.8
[INFO] [stderr]   Downloaded futures-join-macro-preview v0.3.0-alpha.18
[INFO] [stderr]   Downloaded futures-timer v0.3.0
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-2/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:d92eaeed33fa75130ca1ee6c8a01d1ffb62bac859dfdfb3450e3e5d1c0146529" "/opt/rustwide/cargo-home/bin/cargo" "+beta-2020-08-29" "metadata" "--no-deps" "--format-version=1", 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] 66744b8b796c8b840e80b572efc2272590b426d467737e7dc085b3afa00ec76b
[INFO] running `Command { std: "docker" "start" "-a" "66744b8b796c8b840e80b572efc2272590b426d467737e7dc085b3afa00ec76b", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "66744b8b796c8b840e80b572efc2272590b426d467737e7dc085b3afa00ec76b", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "66744b8b796c8b840e80b572efc2272590b426d467737e7dc085b3afa00ec76b", kill_on_drop: false }`
[INFO] [stdout] 66744b8b796c8b840e80b572efc2272590b426d467737e7dc085b3afa00ec76b
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-2/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" "RUSTDOCFLAGS=--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:d92eaeed33fa75130ca1ee6c8a01d1ffb62bac859dfdfb3450e3e5d1c0146529" "/opt/rustwide/cargo-home/bin/cargo" "+beta-2020-08-29" "doc" "--frozen" "--no-deps" "--document-private-items" "--message-format=json", kill_on_drop: false }`
[INFO] [stdout] 06e0611b3fae73b8c920d093bec77cf56477a46eeb61cc19842769a57fecc598
[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" "06e0611b3fae73b8c920d093bec77cf56477a46eeb61cc19842769a57fecc598", kill_on_drop: false }`
[INFO] [stderr]    Compiling syn v0.15.44
[INFO] [stderr]     Checking futures-core-preview v0.3.0-alpha.18
[INFO] [stderr]    Compiling proc-macro2 v1.0.19
[INFO] [stderr]     Checking futures-io-preview v0.3.0-alpha.18
[INFO] [stderr]     Checking async-datagram v3.0.0
[INFO] [stderr]     Checking match_cfg v0.1.0
[INFO] [stderr]     Checking async-ready v3.0.0
[INFO] [stderr]     Checking lru-cache v0.1.2
[INFO] [stderr]     Checking bytes v0.4.12
[INFO] [stderr]     Checking tokio-threadpool v0.1.18
[INFO] [stderr]     Checking mio-uds v0.6.8
[INFO] [stderr]     Checking crossbeam v0.7.3
[INFO] [stderr]     Checking hostname v0.3.1
[INFO] [stderr]     Checking resolv-conf v0.6.3
[INFO] [stderr]     Checking futures-sink-preview v0.3.0-alpha.18
[INFO] [stderr]     Checking futures-channel-preview v0.3.0-alpha.18
[INFO] [stderr]     Checking tokio-io v0.1.13
[INFO] [stderr]    Compiling quote v1.0.7
[INFO] [stderr]     Checking tokio-reactor v0.1.12
[INFO] [stderr]     Checking tokio-codec v0.1.2
[INFO] [stderr]     Checking tokio-fs v0.1.7
[INFO] [stderr]    Compiling syn v1.0.39
[INFO] [stderr]     Checking tokio-tcp v0.1.4
[INFO] [stderr]     Checking tokio-udp v0.1.6
[INFO] [stderr]     Checking tokio-uds v0.2.7
[INFO] [stderr]     Checking tokio v0.1.22
[INFO] [stderr]    Compiling futures-select-macro-preview v0.3.0-alpha.18
[INFO] [stderr]    Compiling futures-join-macro-preview v0.3.0-alpha.18
[INFO] [stderr]    Compiling enum-as-inner v0.2.1
[INFO] [stderr]    Compiling synstructure v0.12.4
[INFO] [stderr]     Checking futures-util-preview v0.3.0-alpha.18
[INFO] [stdout] error[E0554]: `#![feature]` may not be used on the beta release channel
[INFO] [stdout]  --> /opt/rustwide/cargo-home/registry/src/github.com-1ecc6299db9ec823/futures-util-preview-0.3.0-alpha.18/src/lib.rs:4:38
[INFO] [stdout]   |
[INFO] [stdout] 4 | #![cfg_attr(feature = "async-await", feature(async_await))]
[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 `futures-util-preview`.
[INFO] [stderr] 
[INFO] [stderr] To learn more, run the command again with --verbose.
[INFO] [stderr] warning: build failed, waiting for other jobs to finish...
[INFO] [stderr] error: build failed
[INFO] running `Command { std: "docker" "inspect" "06e0611b3fae73b8c920d093bec77cf56477a46eeb61cc19842769a57fecc598", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "06e0611b3fae73b8c920d093bec77cf56477a46eeb61cc19842769a57fecc598", kill_on_drop: false }`
[INFO] [stdout] 06e0611b3fae73b8c920d093bec77cf56477a46eeb61cc19842769a57fecc598