warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.53.0`
       --> src/identifier.rs:331:40
        |
    331 |     let zero_bits_on_string_end = repr.leading_zeros();
        |                                        ^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv
        = note: `-W clippy::incompatible-msrv` implied by `-W clippy::all`
        = help: to override `-W clippy::all` add `#[allow(clippy::incompatible_msrv)]`

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.53.0`
       --> src/identifier.rs:420:37
        |
    420 |     let len_bits = usize_bits - len.leading_zeros() as usize;
        |                                     ^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.45.0`
      --> src/parse.rs:48:52
       |
    48 |         let (pre, text) = if let Some(text) = text.strip_prefix('-') {
       |                                                    ^^^^^^^^^^^^^^^^^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.45.0`
      --> src/parse.rs:59:54
       |
    59 |         let (build, text) = if let Some(text) = text.strip_prefix('+') {
       |                                                      ^^^^^^^^^^^^^^^^^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.45.0`
       --> src/parse.rs:192:31
        |
    192 |     if let Some(rest) = input.strip_prefix('*') {
        |                               ^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.45.0`
       --> src/parse.rs:194:38
        |
    194 |     } else if let Some(rest) = input.strip_prefix('x') {
        |                                      ^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.45.0`
       --> src/parse.rs:196:38
        |
    196 |     } else if let Some(rest) = input.strip_prefix('X') {
        |                                      ^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.45.0`
       --> src/parse.rs:204:31
        |
    204 |     if let Some(rest) = input.strip_prefix('.') {
        |                               ^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.45.0`
       --> src/parse.rs:301:50
        |
    301 |     let (minor, text) = if let Some(text) = text.strip_prefix('.') {
        |                                                  ^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.45.0`
       --> src/parse.rs:317:50
        |
    317 |     let (patch, text) = if let Some(text) = text.strip_prefix('.') {
        |                                                  ^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.37.0`
       --> src/parse.rs:387:22
        |
    387 |         unsafe { out.as_mut_ptr().add(depth).write(comparator) }
        |                      ^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.45.0`
       --> src/parse.rs:391:41
        |
    391 |     let text = if let Some(text) = text.strip_prefix(',') {
        |                                         ^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: current MSRV (Minimum Supported Rust Version) is `1.31.0` but this item is stable since `1.37.0`
       --> src/parse.rs:407:18
        |
    407 |     unsafe { out.as_mut_ptr().add(depth).write(comparator) }
        |                  ^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

    warning: the item `Vec` is imported redundantly
       --> src/lib.rs:103:5
        |
    103 | use crate::alloc::vec::Vec;
        |     ^^^^^^^^^^^^^^^^^^^^^^
    ...
    109 | use crate::backport::*;
        |     ------------------ the item `Vec` is already imported here
        |
        = note: `#[warn(unused_imports)]` on by default

Debugging a recent cargo-outdated bug, it would have been nice not to
wonder whether a rustc version change in GitHub's runner image was a
contributing factor.

chore: fix typo in safety comment

This reverts commit 6e6ba22.

    warning: unexpected `cfg` condition name: `doc_cfg`
      --> src/lib.rs:64:13
       |
    64 | #![cfg_attr(doc_cfg, feature(doc_cfg))]
       |             ^^^^^^^
       |
       = help: expected names are: `clippy`, `debug_assertions`, `doc`, `docsrs`, `doctest`, `feature`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `target_abi`, `target_arch`, `target_endian`, `target_env`, `target_family`, `target_feature`, `target_has_atomic`, `target_has_atomic_equal_alignment`, `target_has_atomic_load_store`, `target_os`, `target_pointer_width`, `target_thread_local`, `target_vendor`, `test`, `ub_checks`, `unix`, `windows`
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(doc_cfg)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration
       = note: `#[warn(unexpected_cfgs)]` on by default

    warning: unexpected `cfg` condition name: `no_alloc_crate`
      --> src/lib.rs:65:43
       |
    65 | #![cfg_attr(all(not(feature = "std"), not(no_alloc_crate)), no_std)]
       |                                           ^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_alloc_crate)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_unsafe_op_in_unsafe_fn_lint`
      --> src/lib.rs:66:17
       |
    66 | #![cfg_attr(not(no_unsafe_op_in_unsafe_fn_lint), deny(unsafe_op_in_unsafe_fn))]
       |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_unsafe_op_in_unsafe_fn_lint)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_unsafe_op_in_unsafe_fn_lint`
      --> src/lib.rs:67:13
       |
    67 | #![cfg_attr(no_unsafe_op_in_unsafe_fn_lint, allow(unused_unsafe))]
       |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_unsafe_op_in_unsafe_fn_lint)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_str_strip_prefix`
      --> src/lib.rs:68:13
       |
    68 | #![cfg_attr(no_str_strip_prefix, allow(unstable_name_collisions))]
       |             ^^^^^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_str_strip_prefix)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_alloc_crate`
      --> src/lib.rs:89:11
       |
    89 | #[cfg(not(no_alloc_crate))]
       |           ^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_alloc_crate)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_const_vec_new`
       --> src/lib.rs:188:12
        |
    188 | #[cfg_attr(no_const_vec_new, derive(Default))]
        |            ^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_const_vec_new)");` to the top of the `build.rs`
        = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_non_exhaustive`
       --> src/lib.rs:252:16
        |
    252 | #[cfg_attr(not(no_non_exhaustive), non_exhaustive)]
        |                ^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_non_exhaustive)");` to the top of the `build.rs`
        = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_const_vec_new`
       --> src/lib.rs:529:11
        |
    529 | #[cfg(not(no_const_vec_new))]
        |           ^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_const_vec_new)");` to the top of the `build.rs`
        = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_non_exhaustive`
       --> src/lib.rs:263:11
        |
    263 |     #[cfg(no_non_exhaustive)] // rustc <1.40
        |           ^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_non_exhaustive)");` to the top of the `build.rs`
        = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_str_strip_prefix`
     --> src/backport.rs:1:7
      |
    1 | #[cfg(no_str_strip_prefix)] // rustc <1.45
      |       ^^^^^^^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_str_strip_prefix)");` to the top of the `build.rs`
      = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_str_strip_prefix`
     --> src/backport.rs:6:7
      |
    6 | #[cfg(no_str_strip_prefix)]
      |       ^^^^^^^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_str_strip_prefix)");` to the top of the `build.rs`
      = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_alloc_crate`
      --> src/backport.rs:19:7
       |
    19 | #[cfg(no_alloc_crate)] // rustc <1.36
       |       ^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_alloc_crate)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_non_exhaustive`
      --> src/display.rs:59:19
       |
    59 |             #[cfg(no_non_exhaustive)]
       |                   ^^^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_non_exhaustive)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `doc_cfg`
      --> src/error.rs:29:12
       |
    29 | #[cfg_attr(doc_cfg, doc(cfg(feature = "std")))]
       |            ^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(doc_cfg)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_non_exhaustive`
      --> src/eval.rs:39:15
       |
    39 |         #[cfg(no_non_exhaustive)]
       |               ^^^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_non_exhaustive)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_exhaustive_int_match`
       --> src/identifier.rs:166:19
        |
    166 |             #[cfg(no_exhaustive_int_match)] // rustc <1.33
        |                   ^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_exhaustive_int_match)");` to the top of the `build.rs`
        = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_nonzero_bitscan`
       --> src/identifier.rs:327:11
        |
    327 |     #[cfg(no_nonzero_bitscan)]
        |           ^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_nonzero_bitscan)");` to the top of the `build.rs`
        = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_nonzero_bitscan`
       --> src/identifier.rs:416:11
        |
    416 |     #[cfg(no_nonzero_bitscan)] // rustc <1.53
        |           ^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_nonzero_bitscan)");` to the top of the `build.rs`
        = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_const_vec_new`
      --> src/parse.rs:92:27
       |
    92 |                 #[cfg(not(no_const_vec_new))]
       |                           ^^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_const_vec_new)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_const_vec_new`
      --> src/parse.rs:94:23
       |
    94 |                 #[cfg(no_const_vec_new)] // rustc <1.39
       |                       ^^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_const_vec_new)");` to the top of the `build.rs`
       = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

    warning: unexpected `cfg` condition name: `no_const_vec_new`
       --> src/lib.rs:497:15
        |
    497 |     #[cfg(not(no_const_vec_new))] // rustc <1.39
        |               ^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_const_vec_new)");` to the top of the `build.rs`
        = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration

Resolve unexpected_cfgs warning