[INFO] fetching crate string-err 0.1.1...
[INFO] testing string-err-0.1.1 against 1.49.0 for beta-1.50-1
[INFO] extracting crate string-err 0.1.1 into /workspace/builds/worker-4/source
[INFO] validating manifest of crates.io crate string-err 0.1.1 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 string-err 0.1.1
[INFO] finished tweaking crates.io crate string-err 0.1.1
[INFO] tweaked toml for crates.io crate string-err 0.1.1 written to /workspace/builds/worker-4/source/Cargo.toml
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+1.49.0" "generate-lockfile" "--manifest-path" "Cargo.toml" "-Zno-index-update", kill_on_drop: false }`
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+1.49.0" "fetch" "--locked" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/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] [stderr] WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
[INFO] [stdout] 2546ea5febe6be7ef89f5399720846beb4d7b1e4314d9cd68ea43a3e075845e5
[INFO] running `Command { std: "docker" "start" "-a" "2546ea5febe6be7ef89f5399720846beb4d7b1e4314d9cd68ea43a3e075845e5", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "2546ea5febe6be7ef89f5399720846beb4d7b1e4314d9cd68ea43a3e075845e5", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "2546ea5febe6be7ef89f5399720846beb4d7b1e4314d9cd68ea43a3e075845e5", kill_on_drop: false }`
[INFO] [stdout] 2546ea5febe6be7ef89f5399720846beb4d7b1e4314d9cd68ea43a3e075845e5
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/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] [stdout] 61689610e49871f2fa925146250612c5de2b680348fe4a2828591687deff1b8a
[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" "61689610e49871f2fa925146250612c5de2b680348fe4a2828591687deff1b8a", kill_on_drop: false }`
[INFO] [stderr]    Compiling string-err v0.1.1 (/opt/rustwide/workdir)
[INFO] [stdout] error[E0554]: `#![feature]` may not be used on the stable release channel
[INFO] [stdout]   --> src/lib.rs:18:1
[INFO] [stdout]    |
[INFO] [stdout] 18 | / #![feature(
[INFO] [stdout] 19 | |     specialization,
[INFO] [stdout] 20 | |     backtrace,
[INFO] [stdout] 21 | |     debug_non_exhaustive,
[INFO] [stdout] 22 | |     external_doc,
[INFO] [stdout] 23 | |     try_trait,
[INFO] [stdout] 24 | | )]
[INFO] [stdout]    | |__^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
[INFO] [stdout]   --> src/lib.rs:19:2
[INFO] [stdout]    |
[INFO] [stdout] 19 |     specialization,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(incomplete_features)]` on by default
[INFO] [stdout]    = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
[INFO] [stdout]    = help: consider using `min_specialization` instead, which is more stable and complete
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] error: aborting due to previous error; 1 warning emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] For more information about this error, try `rustc --explain E0554`.
[INFO] [stdout] 
[INFO] [stderr] error: could not compile `string-err`
[INFO] [stderr] 
[INFO] [stderr] To learn more, run the command again with --verbose.
[INFO] running `Command { std: "docker" "inspect" "61689610e49871f2fa925146250612c5de2b680348fe4a2828591687deff1b8a", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "61689610e49871f2fa925146250612c5de2b680348fe4a2828591687deff1b8a", kill_on_drop: false }`
[INFO] [stdout] 61689610e49871f2fa925146250612c5de2b680348fe4a2828591687deff1b8a