[INFO] fetching crate async-option 0.1.1...
[INFO] checking async-option-0.1.1 against master#c9228570668803e3e6402770d55f23a12c9ae686 for pr-79472
[INFO] extracting crate async-option 0.1.1 into /workspace/builds/worker-12/source
[INFO] validating manifest of crates.io crate async-option 0.1.1 on toolchain c9228570668803e3e6402770d55f23a12c9ae686
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+c9228570668803e3e6402770d55f23a12c9ae686" "read-manifest" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] started tweaking crates.io crate async-option 0.1.1
[INFO] finished tweaking crates.io crate async-option 0.1.1
[INFO] tweaked toml for crates.io crate async-option 0.1.1 written to /workspace/builds/worker-12/source/Cargo.toml
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+c9228570668803e3e6402770d55f23a12c9ae686" "generate-lockfile" "--manifest-path" "Cargo.toml" "-Zno-index-update", kill_on_drop: false }`
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+c9228570668803e3e6402770d55f23a12c9ae686" "fetch" "--locked" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Blocking waiting for file lock on package cache
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-12/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-12/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:c8ac004eab7d63a0ad09a2dde3d3353ba464f767bee4de425dc8f74c46a1905e" "/opt/rustwide/cargo-home/bin/cargo" "+c9228570668803e3e6402770d55f23a12c9ae686" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stdout] 85800e854ebecd6c84f3784550b360470e2a85f76f7502fe9e7d448670d53c25
[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" "85800e854ebecd6c84f3784550b360470e2a85f76f7502fe9e7d448670d53c25", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "85800e854ebecd6c84f3784550b360470e2a85f76f7502fe9e7d448670d53c25", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "85800e854ebecd6c84f3784550b360470e2a85f76f7502fe9e7d448670d53c25", kill_on_drop: false }`
[INFO] [stdout] 85800e854ebecd6c84f3784550b360470e2a85f76f7502fe9e7d448670d53c25
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-12/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-12/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=forbid" "-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:c8ac004eab7d63a0ad09a2dde3d3353ba464f767bee4de425dc8f74c46a1905e" "/opt/rustwide/cargo-home/bin/cargo" "+c9228570668803e3e6402770d55f23a12c9ae686" "check" "--frozen" "--all" "--all-targets" "--message-format=json", kill_on_drop: false }`
[INFO] [stdout] 6ca0741729b6b8ae28541c173b20862f885cdeeee8718ff9043f25ec88f9cdec
[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" "6ca0741729b6b8ae28541c173b20862f885cdeeee8718ff9043f25ec88f9cdec", kill_on_drop: false }`
[INFO] [stderr]     Blocking waiting for file lock on package cache
[INFO] [stderr]     Checking cfg-if v0.1.10
[INFO] [stderr]     Checking lazy_static v1.4.0
[INFO] [stderr]    Compiling log v0.4.11
[INFO] [stderr]     Checking slab v0.4.2
[INFO] [stderr]     Checking tokio-mock-task v0.1.1
[INFO] [stderr]     Checking async-option v0.1.1 (/opt/rustwide/workdir)
[INFO] [stderr]     Checking crossbeam-utils v0.7.2
[INFO] [stderr]     Checking net2 v0.2.36
[INFO] [stderr]     Checking parking_lot_core v0.6.2
[INFO] [stdout] warning: unused return value of `std::mem::replace` that must be used
[INFO] [stdout]   --> src/lib.rs:96:17
[INFO] [stdout]    |
[INFO] [stdout] 96 |                 mem::replace(self, CellValue::Fin(None));
[INFO] [stdout]    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(unused_must_use)]` on by default
[INFO] [stdout]    = note: if you don't need the old value, you can just assign the new value directly
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: 1 warning emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr]     Checking parking_lot v0.9.0
[INFO] [stderr]     Checking tokio-executor v0.1.10
[INFO] [stderr]     Checking crossbeam-epoch v0.8.2
[INFO] [stderr]     Checking crossbeam-queue v0.2.3
[INFO] [stderr]     Checking tokio-io v0.1.13
[INFO] [stderr]     Checking mio v0.6.23
[INFO] [stderr]     Checking tokio-timer v0.2.13
[INFO] [stderr]     Checking tokio-current-thread v0.1.7
[INFO] [stderr]     Checking crossbeam-deque v0.7.3
[INFO] [stderr]     Checking tokio-threadpool v0.1.18
[INFO] [stderr]     Checking tokio-codec v0.1.2
[INFO] [stderr]     Checking tokio-reactor v0.1.12
[INFO] [stderr]     Checking mio-uds v0.6.8
[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-fs v0.1.7
[INFO] [stderr]     Checking tokio v0.1.22
[INFO] [stdout] error: unused return value of `std::mem::replace` that must be used
[INFO] [stdout]   --> src/lib.rs:96:17
[INFO] [stdout]    |
[INFO] [stdout] 96 |                 mem::replace(self, CellValue::Fin(None));
[INFO] [stdout]    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout] note: the lint level is defined here
[INFO] [stdout]   --> src/lib.rs:26:24
[INFO] [stdout]    |
[INFO] [stdout] 26 | #![cfg_attr(test, deny(warnings))]
[INFO] [stdout]    |                        ^^^^^^^^
[INFO] [stdout]    = note: `#[deny(unused_must_use)]` implied by `#[deny(warnings)]`
[INFO] [stdout]    = note: if you don't need the old value, you can just assign the new value directly
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] error: aborting due to previous error
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr] error: could not compile `async-option`
[INFO] [stderr] 
[INFO] [stderr] To learn more, run the command again with --verbose.
[INFO] running `Command { std: "docker" "inspect" "6ca0741729b6b8ae28541c173b20862f885cdeeee8718ff9043f25ec88f9cdec", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "6ca0741729b6b8ae28541c173b20862f885cdeeee8718ff9043f25ec88f9cdec", kill_on_drop: false }`
[INFO] [stdout] 6ca0741729b6b8ae28541c173b20862f885cdeeee8718ff9043f25ec88f9cdec