[INFO] fetching crate postfix 0.1.2...
[INFO] testing postfix-0.1.2 against try#722e1797249a965b6335aebd65d777f917e498f1 for pr-91031
[INFO] extracting crate postfix 0.1.2 into /workspace/builds/worker-4/source
[INFO] validating manifest of crates.io crate postfix 0.1.2 on toolchain 722e1797249a965b6335aebd65d777f917e498f1
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+722e1797249a965b6335aebd65d777f917e498f1" "metadata" "--manifest-path" "Cargo.toml" "--no-deps", kill_on_drop: false }`
[INFO] started tweaking crates.io crate postfix 0.1.2
[INFO] finished tweaking crates.io crate postfix 0.1.2
[INFO] tweaked toml for crates.io crate postfix 0.1.2 written to /workspace/builds/worker-4/source/Cargo.toml
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+722e1797249a965b6335aebd65d777f917e498f1" "generate-lockfile" "--manifest-path" "Cargo.toml" "-Zno-index-update", kill_on_drop: false }`
[INFO] running `Command { std: "/workspace/cargo-home/bin/cargo" "+722e1797249a965b6335aebd65d777f917e498f1" "fetch" "--manifest-path" "Cargo.toml", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/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@sha256:5736fa189c1c60b01babf4b8b698fe57b6ecc41933a7ff2e0b8d7a221459412b" "/opt/rustwide/cargo-home/bin/cargo" "+722e1797249a965b6335aebd65d777f917e498f1" "metadata" "--no-deps" "--format-version=1", kill_on_drop: false }`
[INFO] [stderr] WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
[INFO] [stdout] 52545f1d69f1a5fd5bdedea959774156b73888ecb0fdca39c97ce544056b812e
[INFO] running `Command { std: "docker" "start" "-a" "52545f1d69f1a5fd5bdedea959774156b73888ecb0fdca39c97ce544056b812e", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "inspect" "52545f1d69f1a5fd5bdedea959774156b73888ecb0fdca39c97ce544056b812e", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "52545f1d69f1a5fd5bdedea959774156b73888ecb0fdca39c97ce544056b812e", kill_on_drop: false }`
[INFO] [stdout] 52545f1d69f1a5fd5bdedea959774156b73888ecb0fdca39c97ce544056b812e
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/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@sha256:5736fa189c1c60b01babf4b8b698fe57b6ecc41933a7ff2e0b8d7a221459412b" "/opt/rustwide/cargo-home/bin/cargo" "+722e1797249a965b6335aebd65d777f917e498f1" "build" "--frozen" "--message-format=json", kill_on_drop: false }`
[INFO] [stderr] WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
[INFO] [stdout] 6763c3b71a0b1df8ba39848125b5471c48b0b06aae0bda14f9b85330769c3be3
[INFO] running `Command { std: "docker" "start" "-a" "6763c3b71a0b1df8ba39848125b5471c48b0b06aae0bda14f9b85330769c3be3", kill_on_drop: false }`
[INFO] [stderr]    Compiling postfix v0.1.2 (/opt/rustwide/workdir)
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]  --> src/operator.rs:2:15
[INFO] [stdout]   |
[INFO] [stdout] 2 |     Unary(&'a Fn(f64) -> Result<f64, &'static str>),
[INFO] [stdout]   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64) -> Result<f64, &'static str>`
[INFO] [stdout]   |
[INFO] [stdout]   = note: `#[warn(bare_trait_objects)]` on by default
[INFO] [stdout]   = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]  --> src/operator.rs:3:16
[INFO] [stdout]   |
[INFO] [stdout] 3 |     Binary(&'a Fn(f64, f64) -> Result<f64, &'static str>),
[INFO] [stdout]   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64, f64) -> Result<f64, &'static str>`
[INFO] [stdout]   |
[INFO] [stdout]   = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/operator.rs:14:25
[INFO] [stdout]    |
[INFO] [stdout] 14 |     pub fn unary(f: &'a Fn(f64) -> Result<f64, &'static str>) -> Self {
[INFO] [stdout]    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64) -> Result<f64, &'static str>`
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/operator.rs:18:26
[INFO] [stdout]    |
[INFO] [stdout] 18 |     pub fn binary(f: &'a Fn(f64, f64) -> Result<f64, &'static str>) -> Self {
[INFO] [stdout]    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64, f64) -> Result<f64, &'static str>`
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: 4 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr]     Finished dev [unoptimized + debuginfo] target(s) in 0.79s
[INFO] running `Command { std: "docker" "inspect" "6763c3b71a0b1df8ba39848125b5471c48b0b06aae0bda14f9b85330769c3be3", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "6763c3b71a0b1df8ba39848125b5471c48b0b06aae0bda14f9b85330769c3be3", kill_on_drop: false }`
[INFO] [stdout] 6763c3b71a0b1df8ba39848125b5471c48b0b06aae0bda14f9b85330769c3be3
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/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@sha256:5736fa189c1c60b01babf4b8b698fe57b6ecc41933a7ff2e0b8d7a221459412b" "/opt/rustwide/cargo-home/bin/cargo" "+722e1797249a965b6335aebd65d777f917e498f1" "test" "--frozen" "--no-run" "--message-format=json", kill_on_drop: false }`
[INFO] [stderr] WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
[INFO] [stdout] 36bff206691eccfb6532e0387079ca3d537dc26433d0131ea23ce8cf0a394010
[INFO] running `Command { std: "docker" "start" "-a" "36bff206691eccfb6532e0387079ca3d537dc26433d0131ea23ce8cf0a394010", kill_on_drop: false }`
[INFO] [stderr]     Blocking waiting for file lock on package cache
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]  --> src/operator.rs:2:15
[INFO] [stdout]   |
[INFO] [stdout] 2 |     Unary(&'a Fn(f64) -> Result<f64, &'static str>),
[INFO] [stdout]   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64) -> Result<f64, &'static str>`
[INFO] [stdout]   |
[INFO] [stdout]   = note: `#[warn(bare_trait_objects)]` on by default
[INFO] [stdout]   = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stderr]    Compiling postfix v0.1.2 (/opt/rustwide/workdir)
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]  --> src/operator.rs:3:16
[INFO] [stdout]   |
[INFO] [stdout] 3 |     Binary(&'a Fn(f64, f64) -> Result<f64, &'static str>),
[INFO] [stdout]   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64, f64) -> Result<f64, &'static str>`
[INFO] [stdout]   |
[INFO] [stdout]   = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/operator.rs:14:25
[INFO] [stdout]    |
[INFO] [stdout] 14 |     pub fn unary(f: &'a Fn(f64) -> Result<f64, &'static str>) -> Self {
[INFO] [stdout]    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64) -> Result<f64, &'static str>`
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/operator.rs:18:26
[INFO] [stdout]    |
[INFO] [stdout] 18 |     pub fn binary(f: &'a Fn(f64, f64) -> Result<f64, &'static str>) -> Self {
[INFO] [stdout]    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64, f64) -> Result<f64, &'static str>`
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: 4 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]  --> src/operator.rs:2:15
[INFO] [stdout]   |
[INFO] [stdout] 2 |     Unary(&'a Fn(f64) -> Result<f64, &'static str>),
[INFO] [stdout]   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64) -> Result<f64, &'static str>`
[INFO] [stdout]   |
[INFO] [stdout]   = note: `#[warn(bare_trait_objects)]` on by default
[INFO] [stdout]   = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]  --> src/operator.rs:3:16
[INFO] [stdout]   |
[INFO] [stdout] 3 |     Binary(&'a Fn(f64, f64) -> Result<f64, &'static str>),
[INFO] [stdout]   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64, f64) -> Result<f64, &'static str>`
[INFO] [stdout]   |
[INFO] [stdout]   = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/operator.rs:14:25
[INFO] [stdout]    |
[INFO] [stdout] 14 |     pub fn unary(f: &'a Fn(f64) -> Result<f64, &'static str>) -> Self {
[INFO] [stdout]    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64) -> Result<f64, &'static str>`
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stdout]   --> src/operator.rs:18:26
[INFO] [stdout]    |
[INFO] [stdout] 18 |     pub fn binary(f: &'a Fn(f64, f64) -> Result<f64, &'static str>) -> Self {
[INFO] [stdout]    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64, f64) -> Result<f64, &'static str>`
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stdout] 
[INFO] [stdout] warning: 4 warnings emitted
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stderr]     Finished test [unoptimized + debuginfo] target(s) in 1.21s
[INFO] running `Command { std: "docker" "inspect" "36bff206691eccfb6532e0387079ca3d537dc26433d0131ea23ce8cf0a394010", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "36bff206691eccfb6532e0387079ca3d537dc26433d0131ea23ce8cf0a394010", kill_on_drop: false }`
[INFO] [stdout] 36bff206691eccfb6532e0387079ca3d537dc26433d0131ea23ce8cf0a394010
[INFO] running `Command { std: "docker" "create" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/target:/opt/rustwide/target:rw,Z" "-v" "/var/lib/crater-agent-workspace/builds/worker-4/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@sha256:5736fa189c1c60b01babf4b8b698fe57b6ecc41933a7ff2e0b8d7a221459412b" "/opt/rustwide/cargo-home/bin/cargo" "+722e1797249a965b6335aebd65d777f917e498f1" "test" "--frozen", kill_on_drop: false }`
[INFO] [stdout] 755254806b4c7ef8413f307e10447bc3bb77ead32591888e4abf6e6180bce040
[INFO] [stderr] WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
[INFO] running `Command { std: "docker" "start" "-a" "755254806b4c7ef8413f307e10447bc3bb77ead32591888e4abf6e6180bce040", kill_on_drop: false }`
[INFO] [stderr] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stderr]  --> src/operator.rs:2:15
[INFO] [stderr]   |
[INFO] [stderr] 2 |     Unary(&'a Fn(f64) -> Result<f64, &'static str>),
[INFO] [stderr]   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64) -> Result<f64, &'static str>`
[INFO] [stderr]   |
[INFO] [stderr]   = note: `#[warn(bare_trait_objects)]` on by default
[INFO] [stderr]   = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stderr] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stderr]  --> src/operator.rs:3:16
[INFO] [stderr]   |
[INFO] [stderr] 3 |     Binary(&'a Fn(f64, f64) -> Result<f64, &'static str>),
[INFO] [stderr]   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64, f64) -> Result<f64, &'static str>`
[INFO] [stderr]   |
[INFO] [stderr]   = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stderr] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stderr]   --> src/operator.rs:14:25
[INFO] [stderr]    |
[INFO] [stderr] 14 |     pub fn unary(f: &'a Fn(f64) -> Result<f64, &'static str>) -> Self {
[INFO] [stderr]    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64) -> Result<f64, &'static str>`
[INFO] [stderr]    |
[INFO] [stderr]    = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stderr] warning: trait objects without an explicit `dyn` are deprecated
[INFO] [stderr]   --> src/operator.rs:18:26
[INFO] [stderr]    |
[INFO] [stderr] 18 |     pub fn binary(f: &'a Fn(f64, f64) -> Result<f64, &'static str>) -> Self {
[INFO] [stderr]    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn(f64, f64) -> Result<f64, &'static str>`
[INFO] [stderr]    |
[INFO] [stderr]    = warning: this is accepted in the current edition (Rust 2018) 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] 
[INFO] [stderr] warning: `postfix` (lib) generated 4 warnings
[INFO] [stderr] warning: `postfix` (lib test) generated 4 warnings (4 duplicates)
[INFO] [stderr]     Finished test [unoptimized + debuginfo] target(s) in 0.09s
[INFO] [stdout] 
[INFO] [stderr]      Running unittests (/opt/rustwide/target/debug/deps/postfix-8a08852b3dcca77f)
[INFO] [stdout] running 8 tests
[INFO] [stdout] test tests::it_adds ... ok
[INFO] [stdout] test tests::it_divides ... ok
[INFO] [stdout] test tests::it_subtracts ... ok
[INFO] [stderr]    Doc-tests postfix
[INFO] [stdout] test tests::it_divides_by_zero ... ok
[INFO] [stdout] test tests::it_uses_custom_operators ... ok
[INFO] [stdout] test tests::it_respects_precedence ... ok
[INFO] [stdout] test tests::it_multiplies ... ok
[INFO] [stdout] test tests::it_adds_3 ... ok
[INFO] [stdout] 
[INFO] [stdout] test result: ok. 8 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s
[INFO] [stdout] 
[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" "755254806b4c7ef8413f307e10447bc3bb77ead32591888e4abf6e6180bce040", kill_on_drop: false }`
[INFO] running `Command { std: "docker" "rm" "-f" "755254806b4c7ef8413f307e10447bc3bb77ead32591888e4abf6e6180bce040", kill_on_drop: false }`
[INFO] [stdout] 755254806b4c7ef8413f307e10447bc3bb77ead32591888e4abf6e6180bce040