[INFO] cloning repository https://github.com/tylerreisinger/neural-network-deep-learning
[INFO] running `Command { std: "git" "-c" "credential.helper=" "-c" "credential.helper=/workspace/cargo-home/bin/git-credential-null" "clone" "--bare" "https://github.com/tylerreisinger/neural-network-deep-learning" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Ftylerreisinger%2Fneural-network-deep-learning", kill_on_drop: false }`
[INFO] [stderr] Cloning into bare repository '/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Ftylerreisinger%2Fneural-network-deep-learning'...
[INFO] running `Command { std: "git" "rev-parse" "HEAD", kill_on_drop: false }`
[INFO] [stdout] e9b993dc16ba212952631e2fa08a1b63ac1c99fb
[INFO] testing tylerreisinger/neural-network-deep-learning against beta-2022-02-22 for beta-1.60-1
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Ftylerreisinger%2Fneural-network-deep-learning" "/workspace/builds/worker-27/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-27/source'...
[INFO] [stderr] done.
[INFO] validating manifest of git repo https://github.com/tylerreisinger/neural-network-deep-learning on toolchain beta-2022-02-22
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+beta-2022-02-22" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking git repo https://github.com/tylerreisinger/neural-network-deep-learning
[INFO] finished tweaking git repo https://github.com/tylerreisinger/neural-network-deep-learning
[INFO] tweaked toml for git repo https://github.com/tylerreisinger/neural-network-deep-learning written to /workspace/builds/worker-27/source/Cargo.toml
[INFO] crate git repo https://github.com/tylerreisinger/neural-network-deep-learning already has a lockfile, it will not be regenerated
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+beta-2022-02-22" "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] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-27/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-27/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@sha256:0cd99ca24d8e8c98e67c542213511d985b8778b5bdcbb160e038429496686047" "/opt/rustwide/cargo-home/bin/cargo" "+beta-2022-02-22" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stdout] 9dbe9810690833d21213b3411d1cd24f228a1de27c8710d154a11eb568e102de
[INFO] running `Command { std: "docker" "start" "-a" "9dbe9810690833d21213b3411d1cd24f228a1de27c8710d154a11eb568e102de", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "9dbe9810690833d21213b3411d1cd24f228a1de27c8710d154a11eb568e102de", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "9dbe9810690833d21213b3411d1cd24f228a1de27c8710d154a11eb568e102de", kill_on_drop: false }`
[INFO] [stdout] 9dbe9810690833d21213b3411d1cd24f228a1de27c8710d154a11eb568e102de
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-27/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-27/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" "ghcr.io/rust-lang/crates-build-env/linux@sha256:0cd99ca24d8e8c98e67c542213511d985b8778b5bdcbb160e038429496686047" "/opt/rustwide/cargo-home/bin/cargo" "+beta-2022-02-22" "build" "--frozen" "--message-format=json", kill_on_drop: false }`
[INFO] [stdout] 62192f0d8d9be94855c0d1ba8edcb4755f030651185a87613b21a55b942bd00c
[INFO] running `Command { std: "docker" "start" "-a" "62192f0d8d9be94855c0d1ba8edcb4755f030651185a87613b21a55b942bd00c", kill_on_drop: false }`
[INFO] [stderr]    Compiling byteorder v1.0.0
[INFO] [stderr]    Compiling neural_net v0.1.0 (/opt/rustwide/workdir)
[INFO] [stdout] warning: unnecessary parentheses around assigned value
[INFO] [stdout]    --> src/mnist/idx.rs:150:44
[INFO] [stdout]     |
[INFO] [stdout] 150 |         const BUF_READER_CAPACITY: usize = (1 << 20);
[INFO] [stdout]     |                                            ^       ^
[INFO] [stdout]     |
[INFO] [stdout]     = note: `#[warn(unused_parens)]` on by default
[INFO] [stdout] help: remove these parentheses
[INFO] [stdout]     |
[INFO] [stdout] 150 -         const BUF_READER_CAPACITY: usize = (1 << 20);
[INFO] [stdout] 150 +         const BUF_READER_CAPACITY: usize = 1 << 20;
[INFO] [stdout]     | 
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/mnist/error.rs:48:32
[INFO] [stdout]    |
[INFO] [stdout] 48 |     fn cause(&self) -> Option<&Error> {
[INFO] [stdout]    |                                ^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(bare_trait_objects)]` on by default
[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] 48 -     fn cause(&self) -> Option<&Error> {
[INFO] [stdout] 48 +     fn cause(&self) -> Option<&dyn Error> {
[INFO] [stdout]    | 
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
[INFO] [stdout]   --> src/mnist/error.rs:28:38
[INFO] [stdout]    |
[INFO] [stdout] 28 |                 write!(f, "{}", self.description()),
[INFO] [stdout]    |                                      ^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(deprecated)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
[INFO] [stdout]   --> src/mnist/error.rs:30:38
[INFO] [stdout]    |
[INFO] [stdout] 30 |                 write!(f, "{}", self.description()),
[INFO] [stdout]    |                                      ^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
[INFO] [stdout]   --> src/mnist/error.rs:40:44
[INFO] [stdout]    |
[INFO] [stdout] 40 |             MnistError::Io(ref err) => err.description(),
[INFO] [stdout]    |                                            ^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused variable: `labels`
[INFO] [stdout]   --> src/main.rs:12:9
[INFO] [stdout]    |
[INFO] [stdout] 12 |     let labels = 
[INFO] [stdout]    |         ^^^^^^ help: if this is intentional, prefix it with an underscore: `_labels`
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(unused_variables)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused variable: `images`
[INFO] [stdout]   --> src/main.rs:14:9
[INFO] [stdout]    |
[INFO] [stdout] 14 |     let images = 
[INFO] [stdout]    |         ^^^^^^ help: if this is intentional, prefix it with an underscore: `_images`
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `num_neurons`
[INFO] [stdout]  --> src/net/geom.rs:6:5
[INFO] [stdout]   |
[INFO] [stdout] 6 |     num_neurons: usize,
[INFO] [stdout]   |     ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]   |
[INFO] [stdout]   = note: `#[warn(dead_code)]` on by default
[INFO] [stdout] note: `Geometry` has derived impls for the traits `Debug` and `Clone`, but these are intentionally ignored during dead code analysis
[INFO] [stdout]  --> src/net/geom.rs:3:10
[INFO] [stdout]   |
[INFO] [stdout] 3 | #[derive(Clone, Debug)]
[INFO] [stdout]   |          ^^^^^  ^^^^^
[INFO] [stdout]   = note: this warning originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: 8 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr]     Finished dev [unoptimized + debuginfo] target(s) in 1.49s
[INFO] running `Command { std: "docker" "inspect" "62192f0d8d9be94855c0d1ba8edcb4755f030651185a87613b21a55b942bd00c", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "62192f0d8d9be94855c0d1ba8edcb4755f030651185a87613b21a55b942bd00c", kill_on_drop: false }`
[INFO] [stdout] 62192f0d8d9be94855c0d1ba8edcb4755f030651185a87613b21a55b942bd00c
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-27/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-27/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" "ghcr.io/rust-lang/crates-build-env/linux@sha256:0cd99ca24d8e8c98e67c542213511d985b8778b5bdcbb160e038429496686047" "/opt/rustwide/cargo-home/bin/cargo" "+beta-2022-02-22" "test" "--frozen" "--no-run" "--message-format=json", kill_on_drop: false }`
[INFO] [stdout] e0be1251d8532dcc0e2e21831c4ca3ad1bdb0483d9e97e73302c2adb7211447b
[INFO] running `Command { std: "docker" "start" "-a" "e0be1251d8532dcc0e2e21831c4ca3ad1bdb0483d9e97e73302c2adb7211447b", kill_on_drop: false }`
[INFO] [stderr]    Compiling neural_net v0.1.0 (/opt/rustwide/workdir)
[INFO] [stdout] warning: unnecessary parentheses around assigned value
[INFO] [stdout]    --> src/mnist/idx.rs:150:44
[INFO] [stdout]     |
[INFO] [stdout] 150 |         const BUF_READER_CAPACITY: usize = (1 << 20);
[INFO] [stdout]     |                                            ^       ^
[INFO] [stdout]     |
[INFO] [stdout]     = note: `#[warn(unused_parens)]` on by default
[INFO] [stdout] help: remove these parentheses
[INFO] [stdout]     |
[INFO] [stdout] 150 -         const BUF_READER_CAPACITY: usize = (1 << 20);
[INFO] [stdout] 150 +         const BUF_READER_CAPACITY: usize = 1 << 20;
[INFO] [stdout]     | 
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused import: `super::*`
[INFO] [stdout]    --> src/mnist/idx.rs:402:9
[INFO] [stdout]     |
[INFO] [stdout] 402 |     use super::*;
[INFO] [stdout]     |         ^^^^^^^^
[INFO] [stdout]     |
[INFO] [stdout]     = note: `#[warn(unused_imports)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/mnist/error.rs:48:32
[INFO] [stdout]    |
[INFO] [stdout] 48 |     fn cause(&self) -> Option<&Error> {
[INFO] [stdout]    |                                ^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(bare_trait_objects)]` on by default
[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] 48 -     fn cause(&self) -> Option<&Error> {
[INFO] [stdout] 48 +     fn cause(&self) -> Option<&dyn Error> {
[INFO] [stdout]    | 
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
[INFO] [stdout]   --> src/mnist/error.rs:28:38
[INFO] [stdout]    |
[INFO] [stdout] 28 |                 write!(f, "{}", self.description()),
[INFO] [stdout]    |                                      ^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(deprecated)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
[INFO] [stdout]   --> src/mnist/error.rs:30:38
[INFO] [stdout]    |
[INFO] [stdout] 30 |                 write!(f, "{}", self.description()),
[INFO] [stdout]    |                                      ^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
[INFO] [stdout]   --> src/mnist/error.rs:40:44
[INFO] [stdout]    |
[INFO] [stdout] 40 |             MnistError::Io(ref err) => err.description(),
[INFO] [stdout]    |                                            ^^^^^^^^^^^
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused variable: `labels`
[INFO] [stdout]   --> src/main.rs:12:9
[INFO] [stdout]    |
[INFO] [stdout] 12 |     let labels = 
[INFO] [stdout]    |         ^^^^^^ help: if this is intentional, prefix it with an underscore: `_labels`
[INFO] [stdout]    |
[INFO] [stdout]    = note: `#[warn(unused_variables)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: unused variable: `images`
[INFO] [stdout]   --> src/main.rs:14:9
[INFO] [stdout]    |
[INFO] [stdout] 14 |     let images = 
[INFO] [stdout]    |         ^^^^^^ help: if this is intentional, prefix it with an underscore: `_images`
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: field is never read: `num_neurons`
[INFO] [stdout]  --> src/net/geom.rs:6:5
[INFO] [stdout]   |
[INFO] [stdout] 6 |     num_neurons: usize,
[INFO] [stdout]   |     ^^^^^^^^^^^^^^^^^^
[INFO] [stdout]   |
[INFO] [stdout]   = note: `#[warn(dead_code)]` on by default
[INFO] [stdout] note: `Geometry` has derived impls for the traits `Debug` and `Clone`, but these are intentionally ignored during dead code analysis
[INFO] [stdout]  --> src/net/geom.rs:3:10
[INFO] [stdout]   |
[INFO] [stdout] 3 | #[derive(Clone, Debug)]
[INFO] [stdout]   |          ^^^^^  ^^^^^
[INFO] [stdout]   = note: this warning originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: 9 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr]     Finished test [unoptimized + debuginfo] target(s) in 0.42s
[INFO] running `Command { std: "docker" "inspect" "e0be1251d8532dcc0e2e21831c4ca3ad1bdb0483d9e97e73302c2adb7211447b", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "e0be1251d8532dcc0e2e21831c4ca3ad1bdb0483d9e97e73302c2adb7211447b", kill_on_drop: false }`
[INFO] [stdout] e0be1251d8532dcc0e2e21831c4ca3ad1bdb0483d9e97e73302c2adb7211447b
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-27/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-27/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" "ghcr.io/rust-lang/crates-build-env/linux@sha256:0cd99ca24d8e8c98e67c542213511d985b8778b5bdcbb160e038429496686047" "/opt/rustwide/cargo-home/bin/cargo" "+beta-2022-02-22" "test" "--frozen", kill_on_drop: false }`
[INFO] [stdout] 4e83ea2b38a9df729875098d542afb5aa65aff46f2d8051fd798839d40443df2
[INFO] running `Command { std: "docker" "start" "-a" "4e83ea2b38a9df729875098d542afb5aa65aff46f2d8051fd798839d40443df2", kill_on_drop: false }`
[INFO] [stderr] warning: unnecessary parentheses around assigned value
[INFO] [stderr]    --> src/mnist/idx.rs:150:44
[INFO] [stderr]     |
[INFO] [stderr] 150 |         const BUF_READER_CAPACITY: usize = (1 << 20);
[INFO] [stderr]     |                                            ^       ^
[INFO] [stderr]     |
[INFO] [stderr]     = note: `#[warn(unused_parens)]` on by default
[INFO] [stderr] help: remove these parentheses
[INFO] [stderr]     |
[INFO] [stderr] 150 -         const BUF_READER_CAPACITY: usize = (1 << 20);
[INFO] [stderr] 150 +         const BUF_READER_CAPACITY: usize = 1 << 20;
[INFO] [stderr]     | 
[INFO] [stderr] 
[INFO] [stderr] warning: unused import: `super::*`
[INFO] [stderr]    --> src/mnist/idx.rs:402:9
[INFO] [stderr]     |
[INFO] [stderr] 402 |     use super::*;
[INFO] [stderr]     |         ^^^^^^^^
[INFO] [stderr]     |
[INFO] [stderr]     = note: `#[warn(unused_imports)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stderr]   --> src/mnist/error.rs:48:32
[INFO] [stderr]    |
[INFO] [stderr] 48 |     fn cause(&self) -> Option<&Error> {
[INFO] [stderr]    |                                ^^^^^
[INFO] [stderr]    |
[INFO] [stderr]    = note: `#[warn(bare_trait_objects)]` on by default
[INFO] [stderr]    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
[INFO] [stderr]    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
[INFO] [stderr] help: use `dyn`
[INFO] [stderr]    |
[INFO] [stderr] 48 -     fn cause(&self) -> Option<&Error> {
[INFO] [stderr] 48 +     fn cause(&self) -> Option<&dyn Error> {
[INFO] [stderr]    | 
[INFO] [stderr] 
[INFO] [stderr] warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
[INFO] [stderr]   --> src/mnist/error.rs:28:38
[INFO] [stderr]    |
[INFO] [stderr] 28 |                 write!(f, "{}", self.description()),
[INFO] [stderr]    |                                      ^^^^^^^^^^^
[INFO] [stderr]    |
[INFO] [stderr]    = note: `#[warn(deprecated)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
[INFO] [stderr]   --> src/mnist/error.rs:30:38
[INFO] [stderr]    |
[INFO] [stderr] 30 |                 write!(f, "{}", self.description()),
[INFO] [stderr]    |                                      ^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: use of deprecated associated function `std::error::Error::description`: use the Display impl or to_string()
[INFO] [stderr]   --> src/mnist/error.rs:40:44
[INFO] [stderr]    |
[INFO] [stderr] 40 |             MnistError::Io(ref err) => err.description(),
[INFO] [stderr]    |                                            ^^^^^^^^^^^
[INFO] [stderr] 
[INFO] [stderr] warning: unused variable: `labels`
[INFO] [stderr]   --> src/main.rs:12:9
[INFO] [stderr]    |
[INFO] [stderr] 12 |     let labels = 
[INFO] [stderr]    |         ^^^^^^ help: if this is intentional, prefix it with an underscore: `_labels`
[INFO] [stderr]    |
[INFO] [stderr]    = note: `#[warn(unused_variables)]` on by default
[INFO] [stderr] 
[INFO] [stderr] warning: unused variable: `images`
[INFO] [stderr]   --> src/main.rs:14:9
[INFO] [stderr]    |
[INFO] [stderr] 14 |     let images = 
[INFO] [stderr]    |         ^^^^^^ help: if this is intentional, prefix it with an underscore: `_images`
[INFO] [stderr] 
[INFO] [stderr] warning: field is never read: `num_neurons`
[INFO] [stderr]  --> src/net/geom.rs:6:5
[INFO] [stderr]   |
[INFO] [stderr] 6 |     num_neurons: usize,
[INFO] [stderr]   |     ^^^^^^^^^^^^^^^^^^
[INFO] [stderr]   |
[INFO] [stderr]   = note: `#[warn(dead_code)]` on by default
[INFO] [stderr] note: `Geometry` has derived impls for the traits `Debug` and `Clone`, but these are intentionally ignored during dead code analysis
[INFO] [stderr]  --> src/net/geom.rs:3:10
[INFO] [stderr]   |
[INFO] [stderr] 3 | #[derive(Clone, Debug)]
[INFO] [stderr]   |          ^^^^^  ^^^^^
[INFO] [stderr]   = note: this warning originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
[INFO] [stderr] 
[INFO] [stderr] warning: `neural_net` (bin "neural_net" test) generated 9 warnings
[INFO] [stderr]     Finished test [unoptimized + debuginfo] target(s) in 0.01s
[INFO] [stdout] 
[INFO] [stderr]      Running unittests (/opt/rustwide/target/debug/deps/neural_net-df58355ce5688778)
[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" "4e83ea2b38a9df729875098d542afb5aa65aff46f2d8051fd798839d40443df2", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "4e83ea2b38a9df729875098d542afb5aa65aff46f2d8051fd798839d40443df2", kill_on_drop: false }`
[INFO] [stdout] 4e83ea2b38a9df729875098d542afb5aa65aff46f2d8051fd798839d40443df2