[INFO] fetching crate maybe-serde 0.2.1...
[INFO] testing maybe-serde-0.2.1 against 1.91.0 for beta-1.92-2
[INFO] extracting crate maybe-serde 0.2.1 into /workspace/builds/worker-0-tc1/source
[INFO] started tweaking crates.io crate maybe-serde 0.2.1
[INFO] finished tweaking crates.io crate maybe-serde 0.2.1
[INFO] tweaked toml for crates.io crate maybe-serde 0.2.1 written to /workspace/builds/worker-0-tc1/source/Cargo.toml
[INFO] validating manifest of crates.io crate maybe-serde 0.2.1 on toolchain 1.91.0
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+1.91.0" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+1.91.0" "generate-lockfile" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Updating crates.io index
[INFO] [stderr]      Locking 11 packages to latest compatible versions
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+1.91.0" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc1/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc1/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" "ghcr.io/rust-lang/crates-build-env/linux@sha256:4848fb76d95f26979359cc7e45710b1dbc8f3acb7aeedee7c460d7702230f228" "/opt/rustwide/cargo-home/bin/cargo" "+1.91.0" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stdout] 80fee5902a144a52c0d3d29da9e1871cfb322f20277827d05b700058a7928b4d
[INFO] running `Command { std: "docker" "start" "-a" "80fee5902a144a52c0d3d29da9e1871cfb322f20277827d05b700058a7928b4d", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "80fee5902a144a52c0d3d29da9e1871cfb322f20277827d05b700058a7928b4d", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "80fee5902a144a52c0d3d29da9e1871cfb322f20277827d05b700058a7928b4d", kill_on_drop: false }`
[INFO] [stdout] 80fee5902a144a52c0d3d29da9e1871cfb322f20277827d05b700058a7928b4d
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc1/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-0-tc1/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" "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" "ghcr.io/rust-lang/crates-build-env/linux@sha256:4848fb76d95f26979359cc7e45710b1dbc8f3acb7aeedee7c460d7702230f228" "/opt/rustwide/cargo-home/bin/cargo" "+1.91.0" "build" "--frozen" "--message-format=json", kill_on_drop: false }`
[INFO] [stdout] b0818bf36b2a78d3b4ce0d10518fbb5a5b7a2259cb98eab1468d1621fe1a4213
[INFO] running `Command { std: "docker" "start" "-a" "b0818bf36b2a78d3b4ce0d10518fbb5a5b7a2259cb98eab1468d1621fe1a4213", kill_on_drop: false }`
[INFO] [stderr]    Compiling serde v1.0.228
[INFO] [stderr]    Compiling maybe-serde v0.2.1 (/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(specialization)]
[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:1:12
[INFO] [stdout]   |
[INFO] [stdout] 1 | #![feature(specialization)]
[INFO] [stdout]   |            ^^^^^^^^^^^^^^
[INFO] [stdout]   |
[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]   = note: `#[warn(incomplete_features)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] For more information about this error, try `rustc --explain E0554`.
[INFO] [stdout] 
[INFO] [stderr] error: could not compile `maybe-serde` (lib) due to 1 previous error; 1 warning emitted
[INFO] running `Command { std: "docker" "inspect" "b0818bf36b2a78d3b4ce0d10518fbb5a5b7a2259cb98eab1468d1621fe1a4213", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "b0818bf36b2a78d3b4ce0d10518fbb5a5b7a2259cb98eab1468d1621fe1a4213", kill_on_drop: false }`
[INFO] [stdout] b0818bf36b2a78d3b4ce0d10518fbb5a5b7a2259cb98eab1468d1621fe1a4213