[INFO] cloning repository https://github.com/steffenhaug/freelist
[INFO] running `Command { std: "git" "-c" "credential.helper=" "-c" "credential.helper=/workspace/cargo-home/bin/git-credential-null" "clone" "--bare" "https://github.com/steffenhaug/freelist" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fsteffenhaug%2Ffreelist", kill_on_drop: false }`
[INFO] [stderr] Cloning into bare repository '/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fsteffenhaug%2Ffreelist'...
[INFO] running `Command { std: "git" "rev-parse" "HEAD", kill_on_drop: false }`
[INFO] [stdout] 2e6f8cdbf15480ec39f7c8a8c8e80c100136e42a
[INFO] testing steffenhaug/freelist against try#ce59db7a1b1b012fb2793c4641c1bdecad7a128b for pr-85530
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fsteffenhaug%2Ffreelist" "/workspace/builds/worker-7/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-7/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/steffenhaug/freelist on toolchain ce59db7a1b1b012fb2793c4641c1bdecad7a128b
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+ce59db7a1b1b012fb2793c4641c1bdecad7a128b" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/steffenhaug/freelist
[INFO] finished tweaking git repo https://github.com/steffenhaug/freelist
[INFO] tweaked toml for git repo https://github.com/steffenhaug/freelist written to /workspace/builds/worker-7/source/Cargo.toml
[INFO] crate git repo https://github.com/steffenhaug/freelist already has a lockfile, it will not be regenerated
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+ce59db7a1b1b012fb2793c4641c1bdecad7a128b" "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 failure v0.1.4
[INFO] [stderr]   Downloaded pest_derive v1.0.8
[INFO] [stderr]   Downloaded failure_derive v0.1.4
[INFO] [stderr]   Downloaded criterion-stats v0.3.0
[INFO] [stderr]   Downloaded serde_derive v1.0.83
[INFO] [stderr]   Downloaded criterion-plot v0.2.7
[INFO] [stderr]   Downloaded criterion v0.2.7
[INFO] [stderr]   Downloaded handlebars v1.0.5
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-7/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-7/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@sha256:20528e8c29e4536546f0102ce88568b16ea7538393a33fcca951030f7af10457" "/opt/rustwide/cargo-home/bin/cargo" "+ce59db7a1b1b012fb2793c4641c1bdecad7a128b" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stdout] 8297fe5b56a70a8c100c8f6699a652ace923da789b1b1edac891e47f48d913d9
[INFO] running `Command { std: "docker" "start" "-a" "8297fe5b56a70a8c100c8f6699a652ace923da789b1b1edac891e47f48d913d9", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "8297fe5b56a70a8c100c8f6699a652ace923da789b1b1edac891e47f48d913d9", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "8297fe5b56a70a8c100c8f6699a652ace923da789b1b1edac891e47f48d913d9", kill_on_drop: false }`
[INFO] [stdout] 8297fe5b56a70a8c100c8f6699a652ace923da789b1b1edac891e47f48d913d9
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-7/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-7/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" "ghcr.io/rust-lang/crates-build-env/linux@sha256:20528e8c29e4536546f0102ce88568b16ea7538393a33fcca951030f7af10457" "/opt/rustwide/cargo-home/bin/cargo" "+ce59db7a1b1b012fb2793c4641c1bdecad7a128b" "build" "--frozen" "--message-format=json", kill_on_drop: false }`
[INFO] [stdout] a3bcbc1e7785bbfb8b99e3e567a449ecad2c3d8b9846b13727a4af09572412df
[INFO] running `Command { std: "docker" "start" "-a" "a3bcbc1e7785bbfb8b99e3e567a449ecad2c3d8b9846b13727a4af09572412df", kill_on_drop: false }`
[INFO] [stderr]    Compiling allocators v0.1.0 (/opt/rustwide/workdir)
[INFO] [stdout] warning: unused imports: `RefMut`, `Ref`
[INFO] [stdout]  --> src/pile.rs:2:26
[INFO] [stdout]   |
[INFO] [stdout] 2 | use std::cell::{RefCell, Ref, RefMut};
[INFO] [stdout]   |                          ^^^  ^^^^^^
[INFO] [stdout]   |
[INFO] [stdout]   = note: `#[warn(unused_imports)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused import: `std::fmt`
[INFO] [stdout]  --> src/pile.rs:4:5
[INFO] [stdout]   |
[INFO] [stdout] 4 | use std::fmt;
[INFO] [stdout]   |     ^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `data`
[INFO] [stdout]   --> src/slotmap.rs:10:5
[INFO] [stdout]    |
[INFO] [stdout] 10 |     data:       Vec<Entry<T>>,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(dead_code)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `slots`
[INFO] [stdout]   --> src/slotmap.rs:11:5
[INFO] [stdout]    |
[INFO] [stdout] 11 |     slots:      Vec<Slot>,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `free_data`
[INFO] [stdout]   --> src/slotmap.rs:12:5
[INFO] [stdout]    |
[INFO] [stdout] 12 |     free_data:  Option<usize>,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `free_slots`
[INFO] [stdout]   --> src/slotmap.rs:13:5
[INFO] [stdout]    |
[INFO] [stdout] 13 |     free_slots: Option<usize>
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused return value of `std::mem::replace` that must be used
[INFO] [stdout]   --> src/pile.rs:83:9
[INFO] [stdout]    |
[INFO] [stdout] 83 | /         mem::replace(
[INFO] [stdout] 84 | |             &mut self.memory[address],
[INFO] [stdout] 85 | |             Entry::Free {
[INFO] [stdout] 86 | |                 next: self.free_head,
[INFO] [stdout] 87 | |             },
[INFO] [stdout] 88 | |         );
[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: 7 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused variable: `t`
[INFO] [stdout]   --> src/main.rs:11:9
[INFO] [stdout]    |
[INFO] [stdout] 11 |     let t = fl.remove(x);
[INFO] [stdout]    |         ^ help: if this is intentional, prefix it with an underscore: `_t`
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(unused_variables)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused variable: `u`
[INFO] [stdout]   --> src/main.rs:17:9
[INFO] [stdout]    |
[INFO] [stdout] 17 |     let u = fl.insert(42);
[INFO] [stdout]    |         ^ help: if this is intentional, prefix it with an underscore: `_u`
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused variable: `v`
[INFO] [stdout]   --> src/main.rs:18:9
[INFO] [stdout]    |
[INFO] [stdout] 18 |     let v = fl.insert(69);
[INFO] [stdout]    |         ^ help: if this is intentional, prefix it with an underscore: `_v`
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: 3 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr]     Finished dev [unoptimized + debuginfo] target(s) in 1.15s
[INFO] running `Command { std: "docker" "inspect" "a3bcbc1e7785bbfb8b99e3e567a449ecad2c3d8b9846b13727a4af09572412df", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "a3bcbc1e7785bbfb8b99e3e567a449ecad2c3d8b9846b13727a4af09572412df", kill_on_drop: false }`
[INFO] [stdout] a3bcbc1e7785bbfb8b99e3e567a449ecad2c3d8b9846b13727a4af09572412df
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-7/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-7/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" "ghcr.io/rust-lang/crates-build-env/linux@sha256:20528e8c29e4536546f0102ce88568b16ea7538393a33fcca951030f7af10457" "/opt/rustwide/cargo-home/bin/cargo" "+ce59db7a1b1b012fb2793c4641c1bdecad7a128b" "test" "--frozen" "--no-run" "--message-format=json", kill_on_drop: false }`
[INFO] [stdout] 1de853a3083d9ed68e74f74a5e8a5f21c7d7f3c080137cede61b4f9408f8100c
[INFO] running `Command { std: "docker" "start" "-a" "1de853a3083d9ed68e74f74a5e8a5f21c7d7f3c080137cede61b4f9408f8100c", kill_on_drop: false }`
[INFO] [stderr]    Compiling proc-macro2 v0.4.24
[INFO] [stderr]    Compiling unicode-xid v0.1.0
[INFO] [stderr]    Compiling cc v1.0.28
[INFO] [stderr]    Compiling autocfg v0.1.1
[INFO] [stderr]    Compiling serde v1.0.83
[INFO] [stderr]    Compiling failure_derive v0.1.4
[INFO] [stderr]    Compiling ryu v0.2.7
[INFO] [stderr]    Compiling unicode-xid v0.0.4
[INFO] [stderr]    Compiling ucd-util v0.1.3
[INFO] [stderr]    Compiling regex v1.1.0
[INFO] [stderr]    Compiling rustc-demangle v0.1.11
[INFO] [stderr]    Compiling quote v0.3.15
[INFO] [stderr]    Compiling cast v0.2.2
[INFO] [stderr]    Compiling utf8-ranges v1.0.2
[INFO] [stderr]    Compiling itoa v0.4.3
[INFO] [stderr]    Compiling same-file v1.0.4
[INFO] [stderr]    Compiling byteorder v1.2.7
[INFO] [stdout] warning: unused imports: `RefMut`, `Ref`
[INFO] [stdout]  --> src/pile.rs:2:26
[INFO] [stdout]   |
[INFO] [stdout] 2 | use std::cell::{RefCell, Ref, RefMut};
[INFO] [stdout]   |                          ^^^  ^^^^^^
[INFO] [stdout]   |
[INFO] [stdout]   = note: `#[warn(unused_imports)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused import: `std::fmt`
[INFO] [stdout]  --> src/pile.rs:4:5
[INFO] [stdout]   |
[INFO] [stdout] 4 | use std::fmt;
[INFO] [stdout]   |     ^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `data`
[INFO] [stdout]   --> src/slotmap.rs:10:5
[INFO] [stdout]    |
[INFO] [stdout] 10 |     data:       Vec<Entry<T>>,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(dead_code)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `slots`
[INFO] [stdout]   --> src/slotmap.rs:11:5
[INFO] [stdout]    |
[INFO] [stdout] 11 |     slots:      Vec<Slot>,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `free_data`
[INFO] [stdout]   --> src/slotmap.rs:12:5
[INFO] [stdout]    |
[INFO] [stdout] 12 |     free_data:  Option<usize>,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `free_slots`
[INFO] [stdout]   --> src/slotmap.rs:13:5
[INFO] [stdout]    |
[INFO] [stdout] 13 |     free_slots: Option<usize>
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused return value of `std::mem::replace` that must be used
[INFO] [stdout]   --> src/pile.rs:83:9
[INFO] [stdout]    |
[INFO] [stdout] 83 | /         mem::replace(
[INFO] [stdout] 84 | |             &mut self.memory[address],
[INFO] [stdout] 85 | |             Entry::Free {
[INFO] [stdout] 86 | |                 next: self.free_head,
[INFO] [stdout] 87 | |             },
[INFO] [stdout] 88 | |         );
[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: 7 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr]    Compiling strsim v0.7.0
[INFO] [stderr]    Compiling ansi_term v0.11.0
[INFO] [stderr]    Compiling quick-error v1.2.2
[INFO] [stderr]    Compiling thread-scoped v1.0.2
[INFO] [stderr]    Compiling memchr v2.1.2
[INFO] [stderr]    Compiling lazy_static v1.1.0
[INFO] [stderr]    Compiling textwrap v0.10.0
[INFO] [stderr]    Compiling itertools v0.7.11
[INFO] [stderr]    Compiling rand v0.4.3
[INFO] [stderr]    Compiling itertools-num v0.1.3
[INFO] [stderr]    Compiling regex-syntax v0.6.4
[INFO] [stderr]    Compiling synom v0.11.3
[INFO] [stderr]    Compiling walkdir v2.2.7
[INFO] [stderr]    Compiling clap v2.32.0
[INFO] [stderr]    Compiling syn v0.11.11
[INFO] [stderr]    Compiling backtrace v0.3.13
[INFO] [stderr]    Compiling thread_local v0.3.6
[INFO] [stderr]    Compiling aho-corasick v0.6.9
[INFO] [stderr]    Compiling csv-core v0.1.5
[INFO] [stderr]    Compiling quote v0.6.10
[INFO] [stderr]    Compiling criterion-stats v0.3.0
[INFO] [stderr]    Compiling syn v0.15.23
[INFO] [stderr]    Compiling backtrace-sys v0.1.28
[INFO] [stderr]    Compiling pest_derive v1.0.8
[INFO] [stderr]    Compiling synstructure v0.10.1
[INFO] [stderr]    Compiling serde_json v1.0.33
[INFO] [stderr]    Compiling csv v1.0.5
[INFO] [stderr]    Compiling serde_derive v1.0.83
[INFO] [stderr]    Compiling handlebars v1.0.5
[INFO] [stderr]    Compiling failure v0.1.4
[INFO] [stderr]    Compiling criterion-plot v0.2.7
[INFO] [stderr]    Compiling criterion v0.2.7
[INFO] [stderr]    Compiling allocators v0.1.0 (/opt/rustwide/workdir)
[INFO] [stdout] warning: unused variable: `t`
[INFO] [stdout]   --> src/main.rs:11:9
[INFO] [stdout]    |
[INFO] [stdout] 11 |     let t = fl.remove(x);
[INFO] [stdout]    |         ^ help: if this is intentional, prefix it with an underscore: `_t`
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(unused_variables)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused variable: `u`
[INFO] [stdout]   --> src/main.rs:17:9
[INFO] [stdout]    |
[INFO] [stdout] 17 |     let u = fl.insert(42);
[INFO] [stdout]    |         ^ help: if this is intentional, prefix it with an underscore: `_u`
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused variable: `v`
[INFO] [stdout]   --> src/main.rs:18:9
[INFO] [stdout]    |
[INFO] [stdout] 18 |     let v = fl.insert(69);
[INFO] [stdout]    |         ^ help: if this is intentional, prefix it with an underscore: `_v`
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused imports: `RefMut`, `Ref`
[INFO] [stdout]  --> src/pile.rs:2:26
[INFO] [stdout]   |
[INFO] [stdout] 2 | use std::cell::{RefCell, Ref, RefMut};
[INFO] [stdout]   |                          ^^^  ^^^^^^
[INFO] [stdout]   |
[INFO] [stdout]   = note: `#[warn(unused_imports)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused import: `std::fmt`
[INFO] [stdout]  --> src/pile.rs:4:5
[INFO] [stdout]   |
[INFO] [stdout] 4 | use std::fmt;
[INFO] [stdout]   |     ^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `data`
[INFO] [stdout]   --> src/slotmap.rs:10:5
[INFO] [stdout]    |
[INFO] [stdout] 10 |     data:       Vec<Entry<T>>,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(dead_code)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `slots`
[INFO] [stdout]   --> src/slotmap.rs:11:5
[INFO] [stdout]    |
[INFO] [stdout] 11 |     slots:      Vec<Slot>,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `free_data`
[INFO] [stdout]   --> src/slotmap.rs:12:5
[INFO] [stdout]    |
[INFO] [stdout] 12 |     free_data:  Option<usize>,
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `free_slots`
[INFO] [stdout]   --> src/slotmap.rs:13:5
[INFO] [stdout]    |
[INFO] [stdout] 13 |     free_slots: Option<usize>
[INFO] [stdout]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused return value of `std::mem::replace` that must be used
[INFO] [stdout]   --> src/pile.rs:83:9
[INFO] [stdout]    |
[INFO] [stdout] 83 | /         mem::replace(
[INFO] [stdout] 84 | |             &mut self.memory[address],
[INFO] [stdout] 85 | |             Entry::Free {
[INFO] [stdout] 86 | |                 next: self.free_head,
[INFO] [stdout] 87 | |             },
[INFO] [stdout] 88 | |         );
[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: 3 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: 7 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr]     Finished test [unoptimized + debuginfo] target(s) in 39.85s
[INFO] running `Command { std: "docker" "inspect" "1de853a3083d9ed68e74f74a5e8a5f21c7d7f3c080137cede61b4f9408f8100c", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "1de853a3083d9ed68e74f74a5e8a5f21c7d7f3c080137cede61b4f9408f8100c", kill_on_drop: false }`
[INFO] [stdout] 1de853a3083d9ed68e74f74a5e8a5f21c7d7f3c080137cede61b4f9408f8100c
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-7/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-7/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" "ghcr.io/rust-lang/crates-build-env/linux@sha256:20528e8c29e4536546f0102ce88568b16ea7538393a33fcca951030f7af10457" "/opt/rustwide/cargo-home/bin/cargo" "+ce59db7a1b1b012fb2793c4641c1bdecad7a128b" "test" "--frozen", kill_on_drop: false }`
[INFO] [stdout] c555e0d3f869df4272727e9cf0f041681fffe4851c130e177ddaef6a4f314f08
[INFO] running `Command { std: "docker" "start" "-a" "c555e0d3f869df4272727e9cf0f041681fffe4851c130e177ddaef6a4f314f08", kill_on_drop: false }`
[INFO] [stderr] warning: unused imports: `RefMut`, `Ref`
[INFO] [stderr]  --> src/pile.rs:2:26
[INFO] [stderr]   |
[INFO] [stderr] 2 | use std::cell::{RefCell, Ref, RefMut};
[INFO] [stderr]   |                          ^^^  ^^^^^^
[INFO] [stderr]   |
[INFO] [stderr]   = note: `#[warn(unused_imports)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: unused import: `std::fmt`
[INFO] [stderr]  --> src/pile.rs:4:5
[INFO] [stderr]   |
[INFO] [stderr] 4 | use std::fmt;
[INFO] [stderr]   |     ^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: field is never read: `data`
[INFO] [stderr]   --> src/slotmap.rs:10:5
[INFO] [stderr]    |
[INFO] [stderr] 10 |     data:       Vec<Entry<T>>,
[INFO] [stderr]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr]    |
[INFO] [stderr]    = note: `#[warn(dead_code)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: field is never read: `slots`
[INFO] [stderr]   --> src/slotmap.rs:11:5
[INFO] [stderr]    |
[INFO] [stderr] 11 |     slots:      Vec<Slot>,
[INFO] [stderr]    |     ^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: field is never read: `free_data`
[INFO] [stderr]   --> src/slotmap.rs:12:5
[INFO] [stderr]    |
[INFO] [stderr] 12 |     free_data:  Option<usize>,
[INFO] [stderr]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: field is never read: `free_slots`
[INFO] [stderr]   --> src/slotmap.rs:13:5
[INFO] [stderr]    |
[INFO] [stderr] 13 |     free_slots: Option<usize>
[INFO] [stderr]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: unused return value of `std::mem::replace` that must be used
[INFO] [stderr]   --> src/pile.rs:83:9
[INFO] [stderr]    |
[INFO] [stderr] 83 | /         mem::replace(
[INFO] [stderr] 84 | |             &mut self.memory[address],
[INFO] [stderr] 85 | |             Entry::Free {
[INFO] [stderr] 86 | |                 next: self.free_head,
[INFO] [stderr] 87 | |             },
[INFO] [stderr] 88 | |         );
[INFO] [stderr]    | |__________^
[INFO] [stderr]    |
[INFO] [stderr]    = note: `#[warn(unused_must_use)]` on by default
[INFO] [stderr]    = note: if you don't need the old value, you can just assign the new value directly
[INFO] [stderr] 
[INFO] [stderr] warning: 7 warnings emitted
[INFO] [stderr] 
[INFO] [stderr] warning: unused imports: `RefMut`, `Ref`
[INFO] [stderr]  --> src/pile.rs:2:26
[INFO] [stderr]   |
[INFO] [stderr] 2 | use std::cell::{RefCell, Ref, RefMut};
[INFO] [stderr]   |                          ^^^  ^^^^^^
[INFO] [stderr]   |
[INFO] [stderr]   = note: `#[warn(unused_imports)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: unused import: `std::fmt`
[INFO] [stderr]  --> src/pile.rs:4:5
[INFO] [stderr]   |
[INFO] [stderr] 4 | use std::fmt;
[INFO] [stderr]   |     ^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: field is never read: `data`
[INFO] [stderr]   --> src/slotmap.rs:10:5
[INFO] [stderr]    |
[INFO] [stderr] 10 |     data:       Vec<Entry<T>>,
[INFO] [stderr]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr]    |
[INFO] [stderr]    = note: `#[warn(dead_code)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: field is never read: `slots`
[INFO] [stderr]   --> src/slotmap.rs:11:5
[INFO] [stderr]    |
[INFO] [stderr] 11 |     slots:      Vec<Slot>,
[INFO] [stderr]    |     ^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: field is never read: `free_data`
[INFO] [stderr]   --> src/slotmap.rs:12:5
[INFO] [stderr]    |
[INFO] [stderr] 12 |     free_data:  Option<usize>,
[INFO] [stderr]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: field is never read: `free_slots`
[INFO] [stderr]   --> src/slotmap.rs:13:5
[INFO] [stderr]    |
[INFO] [stderr] 13 |     free_slots: Option<usize>
[INFO] [stderr]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: unused return value of `std::mem::replace` that must be used
[INFO] [stderr]   --> src/pile.rs:83:9
[INFO] [stderr]    |
[INFO] [stderr] 83 | /         mem::replace(
[INFO] [stderr] 84 | |             &mut self.memory[address],
[INFO] [stderr] 85 | |             Entry::Free {
[INFO] [stderr] 86 | |                 next: self.free_head,
[INFO] [stderr] 87 | |             },
[INFO] [stderr] 88 | |         );
[INFO] [stderr]    | |__________^
[INFO] [stderr]    |
[INFO] [stderr]    = note: `#[warn(unused_must_use)]` on by default
[INFO] [stderr]    = note: if you don't need the old value, you can just assign the new value directly
[INFO] [stderr] 
[INFO] [stderr] warning: 7 warnings emitted
[INFO] [stderr] 
[INFO] [stderr] warning: unused variable: `t`
[INFO] [stderr]   --> src/main.rs:11:9
[INFO] [stderr]    |
[INFO] [stderr] 11 |     let t = fl.remove(x);
[INFO] [stderr]    |         ^ help: if this is intentional, prefix it with an underscore: `_t`
[INFO] [stderr]    |
[INFO] [stderr]    = note: `#[warn(unused_variables)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: unused variable: `u`
[INFO] [stderr]   --> src/main.rs:17:9
[INFO] [stderr]    |
[INFO] [stderr] 17 |     let u = fl.insert(42);
[INFO] [stderr]    |         ^ help: if this is intentional, prefix it with an underscore: `_u`
[INFO] [stderr] 
[INFO] [stderr] warning: unused variable: `v`
[INFO] [stderr]   --> src/main.rs:18:9
[INFO] [stderr]    |
[INFO] [stderr] 18 |     let v = fl.insert(69);
[INFO] [stderr]    |         ^ help: if this is intentional, prefix it with an underscore: `_v`
[INFO] [stderr] 
[INFO] [stderr] warning: 3 warnings emitted
[INFO] [stderr] 
[INFO] [stderr]     Finished test [unoptimized + debuginfo] target(s) in 0.04s
[INFO] [stderr]      Running unittests (/opt/rustwide/target/debug/deps/allocators-ab87e6bdac0e2b99)
[INFO] [stdout] 
[INFO] [stdout] running 0 tests
[INFO] [stdout] 
[INFO] [stdout] test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
[INFO] [stdout] 
[INFO] [stderr]      Running unittests (/opt/rustwide/target/debug/deps/executable-69da57cd04f98ee9)
[INFO] [stdout] 
[INFO] [stdout] running 0 tests
[INFO] [stdout] 
[INFO] [stdout] test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
[INFO] [stdout] 
[INFO] [stderr]    Doc-tests allocators
[INFO] [stdout] 
[INFO] [stdout] running 0 tests
[INFO] [stdout] 
[INFO] [stdout] test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
[INFO] [stdout] 
[INFO] running `Command { std: "docker" "inspect" "c555e0d3f869df4272727e9cf0f041681fffe4851c130e177ddaef6a4f314f08", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "c555e0d3f869df4272727e9cf0f041681fffe4851c130e177ddaef6a4f314f08", kill_on_drop: false }`
[INFO] [stdout] c555e0d3f869df4272727e9cf0f041681fffe4851c130e177ddaef6a4f314f08