[INFO] crate tag_safe 0.2.23 is already in cache
[INFO] extracting crate tag_safe 0.2.23 into work/ex/beta-1.38-1/sources/1.37.0/reg/tag_safe/0.2.23
[INFO] extracting crate tag_safe 0.2.23 into work/ex/beta-1.38-1/sources/beta-2019-08-13/reg/tag_safe/0.2.23
[INFO] validating manifest of tag_safe-0.2.23 on toolchain 1.37.0
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+1.37.0" "read-manifest" "--manifest-path" "Cargo.toml"`
[INFO] validating manifest of tag_safe-0.2.23 on toolchain beta-2019-08-13
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+beta-2019-08-13" "read-manifest" "--manifest-path" "Cargo.toml"`
[INFO] started frobbing tag_safe-0.2.23
[INFO] finished frobbing tag_safe-0.2.23
[INFO] frobbed toml for tag_safe-0.2.23 written to work/ex/beta-1.38-1/sources/1.37.0/reg/tag_safe/0.2.23/Cargo.toml
[INFO] started frobbing tag_safe-0.2.23
[INFO] finished frobbing tag_safe-0.2.23
[INFO] frobbed toml for tag_safe-0.2.23 written to work/ex/beta-1.38-1/sources/beta-2019-08-13/reg/tag_safe/0.2.23/Cargo.toml
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+1.37.0" "generate-lockfile" "--manifest-path" "Cargo.toml" "-Zno-index-update"`
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+beta-2019-08-13" "generate-lockfile" "--manifest-path" "Cargo.toml" "-Zno-index-update"`
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+1.37.0" "fetch" "--locked" "--manifest-path" "Cargo.toml"`
[INFO] running `"/mnt/big/crater/work/local/cargo-home/bin/cargo" "+beta-2019-08-13" "fetch" "--locked" "--manifest-path" "Cargo.toml"`
[INFO] testing tag_safe-0.2.23 against 1.37.0 for beta-1.38-1
[INFO] running `"docker" "create" "-v" "/mnt/big/crater/work/local/target-dirs/beta-1.38-1/worker-0/1.37.0:/opt/crater/target:rw,Z" "-v" "/mnt/big/crater/work/ex/beta-1.38-1/sources/1.37.0/reg/tag_safe/0.2.23:/opt/crater/workdir:ro,Z" "-v" "/mnt/big/crater/work/local/cargo-home:/opt/crater/cargo-home:ro,Z" "-v" "/mnt/big/crater/work/local/rustup-home:/opt/crater/rustup-home:ro,Z" "-e" "USER_ID=1000" "-e" "SOURCE_DIR=/opt/crater/workdir" "-e" "MAP_USER_ID=1000" "-e" "CARGO_TARGET_DIR=/opt/crater/target" "-e" "CARGO_INCREMENTAL=0" "-e" "RUST_BACKTRACE=full" "-e" "RUSTFLAGS=--cap-lints=warn" "-e" "CARGO_HOME=/opt/crater/cargo-home" "-e" "RUSTUP_HOME=/opt/crater/rustup-home" "-w" "/opt/crater/workdir" "-m" "1536M" "--network" "none" "rustops/crates-build-env" "/opt/crater/cargo-home/bin/cargo" "+1.37.0" "build" "--frozen"`
[INFO] [stdout] 3a0b1f2b6e6f2a22eb21995e4cc813d70ac94e3e60a08f791d1012d24f085a4d
[INFO] running `"docker" "start" "-a" "3a0b1f2b6e6f2a22eb21995e4cc813d70ac94e3e60a08f791d1012d24f085a4d"`
[INFO] [stderr]    Compiling tag_safe v0.2.23 (/opt/crater/workdir)
[INFO] [stderr] error[E0554]: #![feature] may not be used on the stable release channel
[INFO] [stderr]   --> src/lib.rs:23:1
[INFO] [stderr]    |
[INFO] [stderr] 23 | #![feature(plugin_registrar, rustc_private)]
[INFO] [stderr]    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] error: aborting due to previous error
[INFO] [stderr] 
[INFO] [stderr] For more information about this error, try `rustc --explain E0554`.
[INFO] [stderr] error: Could not compile `tag_safe`.
[INFO] [stderr] 
[INFO] [stderr] To learn more, run the command again with --verbose.
[INFO] running `"docker" "inspect" "3a0b1f2b6e6f2a22eb21995e4cc813d70ac94e3e60a08f791d1012d24f085a4d"`
[INFO] running `"docker" "rm" "-f" "3a0b1f2b6e6f2a22eb21995e4cc813d70ac94e3e60a08f791d1012d24f085a4d"`
[INFO] [stdout] 3a0b1f2b6e6f2a22eb21995e4cc813d70ac94e3e60a08f791d1012d24f085a4d