[INFO] cloning repository https://github.com/davidpeklak/rust-algorithms
[INFO] running `Command { std: "git" "-c" "credential.helper=" "-c" "credential.helper=/workspace/cargo-home/bin/git-credential-null" "clone" "--bare" "https://github.com/davidpeklak/rust-algorithms" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fdavidpeklak%2Frust-algorithms", kill_on_drop: false }`
[INFO] [stderr] Cloning into bare repository '/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fdavidpeklak%2Frust-algorithms'...
[INFO] running `Command { std: "git" "rev-parse" "HEAD", kill_on_drop: false }`
[INFO] [stdout] 9db2d5ac0cfbfe409792033d26d8f4c8aaa3e872
[INFO] checking davidpeklak/rust-algorithms against master#4d1bd0db7f489b22c6d8aa2385937a95412c015b for pr-114682
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fdavidpeklak%2Frust-algorithms" "/workspace/builds/worker-7-tc1/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-7-tc1/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/davidpeklak/rust-algorithms on toolchain 4d1bd0db7f489b22c6d8aa2385937a95412c015b
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+4d1bd0db7f489b22c6d8aa2385937a95412c015b" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/davidpeklak/rust-algorithms
[INFO] finished tweaking git repo https://github.com/davidpeklak/rust-algorithms
[INFO] tweaked toml for git repo https://github.com/davidpeklak/rust-algorithms written to /workspace/builds/worker-7-tc1/source/Cargo.toml
[INFO] crate git repo https://github.com/davidpeklak/rust-algorithms already has a lockfile, it will not be regenerated
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+4d1bd0db7f489b22c6d8aa2385937a95412c015b" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Blocking waiting for file lock on package cache
[ERROR] error running command: no output for 300 seconds
[ERROR] this task or one of its parent failed!
[ERROR] no output for 300 seconds
[ERROR] note: run with `RUST_BACKTRACE=1` to display a backtrace.
[INFO] checking davidpeklak/rust-algorithms against try#785364c7e5e0804473a3fddfb579798ea14e3493 for pr-114682
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fdavidpeklak%2Frust-algorithms" "/workspace/builds/worker-7-tc2/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-7-tc2/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/davidpeklak/rust-algorithms on toolchain 785364c7e5e0804473a3fddfb579798ea14e3493
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+785364c7e5e0804473a3fddfb579798ea14e3493" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/davidpeklak/rust-algorithms
[INFO] finished tweaking git repo https://github.com/davidpeklak/rust-algorithms
[INFO] tweaked toml for git repo https://github.com/davidpeklak/rust-algorithms written to /workspace/builds/worker-7-tc2/source/Cargo.toml
[INFO] crate git repo https://github.com/davidpeklak/rust-algorithms already has a lockfile, it will not be regenerated
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+785364c7e5e0804473a3fddfb579798ea14e3493" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Blocking waiting for file lock on package cache
[INFO] [stderr]     Blocking waiting for file lock on package cache
[ERROR] error running command: no output for 300 seconds
[INFO] checking davidpeklak/rust-algorithms against try#785364c7e5e0804473a3fddfb579798ea14e3493 for pr-114682
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fdavidpeklak%2Frust-algorithms" "/workspace/builds/worker-7-tc2/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-7-tc2/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/davidpeklak/rust-algorithms on toolchain 785364c7e5e0804473a3fddfb579798ea14e3493
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+785364c7e5e0804473a3fddfb579798ea14e3493" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/davidpeklak/rust-algorithms
[INFO] finished tweaking git repo https://github.com/davidpeklak/rust-algorithms
[INFO] tweaked toml for git repo https://github.com/davidpeklak/rust-algorithms written to /workspace/builds/worker-7-tc2/source/Cargo.toml
[INFO] crate git repo https://github.com/davidpeklak/rust-algorithms already has a lockfile, it will not be regenerated
[INFO] running `Command { std: CARGO_HOME="/workspace/cargo-home" RUSTUP_HOME="/workspace/rustup-home" "/workspace/cargo-home/bin/cargo" "+785364c7e5e0804473a3fddfb579798ea14e3493" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] [stderr]     Blocking waiting for file lock on package cache
[INFO] [stderr]     Blocking waiting for file lock on package cache
[INFO] [stderr]  Downloading crates ...
[INFO] [stderr]   Downloaded rand v0.5.0
[INFO] [stderr]   Downloaded rand_core v0.2.0
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-7-tc2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-7-tc2/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@sha256:2788e3201cd34a07e3172128adcd8b3090168a8e3bcc40d7c032b9dda1df7d1c" "/opt/rustwide/cargo-home/bin/cargo" "+785364c7e5e0804473a3fddfb579798ea14e3493" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stdout] ac3961be1d49dae20de0b3f3d139bc2305b00d931a1f701b89a99dd79651752e
[INFO] running `Command { std: "docker" "start" "-a" "ac3961be1d49dae20de0b3f3d139bc2305b00d931a1f701b89a99dd79651752e", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "ac3961be1d49dae20de0b3f3d139bc2305b00d931a1f701b89a99dd79651752e", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "ac3961be1d49dae20de0b3f3d139bc2305b00d931a1f701b89a99dd79651752e", kill_on_drop: false }`
[INFO] [stdout] ac3961be1d49dae20de0b3f3d139bc2305b00d931a1f701b89a99dd79651752e
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-7-tc2/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-7-tc2/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" "RUSTDOCFLAGS=--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" "ghcr.io/rust-lang/crates-build-env/linux@sha256:2788e3201cd34a07e3172128adcd8b3090168a8e3bcc40d7c032b9dda1df7d1c" "/opt/rustwide/cargo-home/bin/cargo" "+785364c7e5e0804473a3fddfb579798ea14e3493" "check" "--frozen" "--all" "--all-targets" "--message-format=json", kill_on_drop: false }`
[INFO] [stdout] a9012388fde275e4acc79bb1c1da74b4d3a7383d36f4cfd3e708e55215c59832
[INFO] running `Command { std: "docker" "start" "-a" "a9012388fde275e4acc79bb1c1da74b4d3a7383d36f4cfd3e708e55215c59832", kill_on_drop: false }`
[INFO] [stderr]    Compiling num-traits v0.2.4
[INFO] [stderr]    Compiling num-integer v0.1.38
[INFO] [stderr]     Checking libc v0.2.41
[INFO] [stderr]     Checking rustc-serialize v0.3.24
[INFO] [stderr]    Compiling num-iter v0.1.37
[INFO] [stderr]     Checking rand_core v0.2.0
[INFO] [stderr]     Checking rand v0.4.2
[INFO] [stderr]     Checking rand v0.5.0
[INFO] [stderr]     Checking num-bigint v0.1.44
[INFO] [stderr]     Checking num-complex v0.1.43
[INFO] [stderr]     Checking num-rational v0.1.42
[INFO] [stderr]     Checking num v0.1.42
[INFO] [stderr]     Checking stopwatch v0.0.7
[INFO] [stderr]     Checking algorithms v0.1.0 (/opt/rustwide/workdir)
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:36:12
[INFO] [stdout]    |
[INFO] [stdout] 36 |     l: &'a LinkedList<Item=T>
[INFO] [stdout]    |            ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout]    = note: `#[warn(bare_trait_objects)]` on by default
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 36 |     l: &'a dyn LinkedList<Item=T>
[INFO] [stdout]    |            +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:65:28
[INFO] [stdout]    |
[INFO] [stdout] 65 | impl<T> LinkedList for Box<LinkedList<Item=T>> {
[INFO] [stdout]    |                            ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 65 | impl<T> LinkedList for Box<dyn LinkedList<Item=T>> {
[INFO] [stdout]    |                            +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:29:41
[INFO] [stdout]    |
[INFO] [stdout] 29 |     fn tail<'a>(&'a self) -> Option<&'a LinkedList<Item=Self::Item>>;
[INFO] [stdout]    |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 29 |     fn tail<'a>(&'a self) -> Option<&'a dyn LinkedList<Item=Self::Item>>;
[INFO] [stdout]    |                                         +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:56:41
[INFO] [stdout]    |
[INFO] [stdout] 56 |     fn tail<'a>(&'a self) -> Option<&'a LinkedList<Item=T>> {
[INFO] [stdout]    |                                         ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 56 |     fn tail<'a>(&'a self) -> Option<&'a dyn LinkedList<Item=T>> {
[INFO] [stdout]    |                                         +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:72:38
[INFO] [stdout]    |
[INFO] [stdout] 72 |     fn tail<'a>(&'a self) -> Option<&LinkedList<Item=T>> {
[INFO] [stdout]    |                                      ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 72 |     fn tail<'a>(&'a self) -> Option<&dyn LinkedList<Item=T>> {
[INFO] [stdout]    |                                      +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:88:41
[INFO] [stdout]    |
[INFO] [stdout] 88 |     fn tail<'a>(&'a self) -> Option<&'a LinkedList<Item=T>> {
[INFO] [stdout]    |                                         ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 88 |     fn tail<'a>(&'a self) -> Option<&'a dyn LinkedList<Item=T>> {
[INFO] [stdout]    |                                         +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:36:12
[INFO] [stdout]    |
[INFO] [stdout] 36 |     l: &'a LinkedList<Item=T>
[INFO] [stdout]    |            ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout]    = note: `#[warn(bare_trait_objects)]` on by default
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 36 |     l: &'a dyn LinkedList<Item=T>
[INFO] [stdout]    |            +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:65:28
[INFO] [stdout]    |
[INFO] [stdout] 65 | impl<T> LinkedList for Box<LinkedList<Item=T>> {
[INFO] [stdout]    |                            ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 65 | impl<T> LinkedList for Box<dyn LinkedList<Item=T>> {
[INFO] [stdout]    |                            +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:29:41
[INFO] [stdout]    |
[INFO] [stdout] 29 |     fn tail<'a>(&'a self) -> Option<&'a LinkedList<Item=Self::Item>>;
[INFO] [stdout]    |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 29 |     fn tail<'a>(&'a self) -> Option<&'a dyn LinkedList<Item=Self::Item>>;
[INFO] [stdout]    |                                         +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:56:41
[INFO] [stdout]    |
[INFO] [stdout] 56 |     fn tail<'a>(&'a self) -> Option<&'a LinkedList<Item=T>> {
[INFO] [stdout]    |                                         ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 56 |     fn tail<'a>(&'a self) -> Option<&'a dyn LinkedList<Item=T>> {
[INFO] [stdout]    |                                         +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:72:38
[INFO] [stdout]    |
[INFO] [stdout] 72 |     fn tail<'a>(&'a self) -> Option<&LinkedList<Item=T>> {
[INFO] [stdout]    |                                      ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 72 |     fn tail<'a>(&'a self) -> Option<&dyn LinkedList<Item=T>> {
[INFO] [stdout]    |                                      +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/lib/linked_list.rs:88:41
[INFO] [stdout]    |
[INFO] [stdout] 88 |     fn tail<'a>(&'a self) -> Option<&'a LinkedList<Item=T>> {
[INFO] [stdout]    |                                         ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]    |
[INFO] [stdout] 88 |     fn tail<'a>(&'a self) -> Option<&'a dyn LinkedList<Item=T>> {
[INFO] [stdout]    |                                         +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]    --> src/lib/linked_list.rs:134:34
[INFO] [stdout]     |
[INFO] [stdout] 134 |     fn some_linked_list() -> Box<LinkedList<Item=i32>> {
[INFO] [stdout]     |                                  ^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]     |
[INFO] [stdout]     = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]     = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]     |
[INFO] [stdout] 134 |     fn some_linked_list() -> Box<dyn LinkedList<Item=i32>> {
[INFO] [stdout]     |                                  +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]    --> src/lib/linked_list.rs:153:41
[INFO] [stdout]     |
[INFO] [stdout] 153 |     fn prepend_some<'a, L>(l: L) -> Box<LinkedList<Item=i32> + 'a>
[INFO] [stdout]     |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]     |
[INFO] [stdout]     = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stdout]     = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stdout] help: use `dyn`
[INFO] [stdout]     |
[INFO] [stdout] 153 |     fn prepend_some<'a, L>(l: L) -> Box<dyn LinkedList<Item=i32> + 'a>
[INFO] [stdout]     |                                         +++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused return value of `std::mem::replace` that must be used
[INFO] [stdout]   --> src/lib/red_black_bst_2.rs:30:9
[INFO] [stdout]    |
[INFO] [stdout] 30 |         mem::replace(&mut self.top, top);
[INFO] [stdout]    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: if you don't need the old value, you can just assign the new value directly
[INFO] [stdout]    = note: `#[warn(unused_must_use)]` on by default
[INFO] [stdout] help: use `let _ = ...` to ignore the resulting value
[INFO] [stdout]    |
[INFO] [stdout] 30 |         let _ = mem::replace(&mut self.top, top);
[INFO] [stdout]    |         +++++++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: 7 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused return value of `std::mem::replace` that must be used
[INFO] [stdout]   --> src/lib/red_black_bst_2.rs:30:9
[INFO] [stdout]    |
[INFO] [stdout] 30 |         mem::replace(&mut self.top, top);
[INFO] [stdout]    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: if you don't need the old value, you can just assign the new value directly
[INFO] [stdout]    = note: `#[warn(unused_must_use)]` on by default
[INFO] [stdout] help: use `let _ = ...` to ignore the resulting value
[INFO] [stdout]    |
[INFO] [stdout] 30 |         let _ = mem::replace(&mut self.top, top);
[INFO] [stdout]    |         +++++++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: 9 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr]     Finished dev [unoptimized + debuginfo] target(s) in 2.23s
[INFO] [stderr] warning: the following packages contain code that will be rejected by a future version of Rust: rustc-serialize v0.3.24
[INFO] [stderr] note: to see what the problems were, use the option `--future-incompat-report`, or run `cargo report future-incompatibilities --id 2`
[INFO] running `Command { std: "docker" "inspect" "a9012388fde275e4acc79bb1c1da74b4d3a7383d36f4cfd3e708e55215c59832", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "a9012388fde275e4acc79bb1c1da74b4d3a7383d36f4cfd3e708e55215c59832", kill_on_drop: false }`
[INFO] [stdout] a9012388fde275e4acc79bb1c1da74b4d3a7383d36f4cfd3e708e55215c59832
