Resolve unexpected_cfgs warning

    warning: unexpected `cfg` condition name: `procmacro2_semver_exempt`
      --> build.rs:48:30
       |
    48 |     let semver_exempt = cfg!(procmacro2_semver_exempt) || docs_rs;
       |                              ^^^^^^^^^^^^^^^^^^^^^^^^
       |
       = 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(procmacro2_semver_exempt)");` 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: `proc_macro_span`
      --> src/lib.rs:90:17
       |
    90 | #![cfg_attr(any(proc_macro_span, super_unstable), feature(proc_macro_span))]
       |                 ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(proc_macro_span)");` 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: `super_unstable`
      --> src/lib.rs:90:34
       |
    90 | #![cfg_attr(any(proc_macro_span, super_unstable), feature(proc_macro_span))]
       |                                  ^^^^^^^^^^^^^^
       |
       = 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(super_unstable)");` 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: `super_unstable`
      --> src/lib.rs:91:13
       |
    91 | #![cfg_attr(super_unstable, feature(proc_macro_def_site))]
       |             ^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(super_unstable)");` 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/lib.rs:92:13
       |
    92 | #![cfg_attr(doc_cfg, feature(doc_cfg))]
       |             ^^^^^^^
       |
       = 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: `procmacro2_semver_exempt`
       --> src/lib.rs:118:11
        |
    118 | #[cfg(all(procmacro2_semver_exempt, wrap_proc_macro, not(super_unstable)))]
        |           ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `wrap_proc_macro`
       --> src/lib.rs:118:37
        |
    118 | #[cfg(all(procmacro2_semver_exempt, wrap_proc_macro, not(super_unstable)))]
        |                                     ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `super_unstable`
       --> src/lib.rs:118:58
        |
    118 | #[cfg(all(procmacro2_semver_exempt, wrap_proc_macro, not(super_unstable)))]
        |                                                          ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(super_unstable)");` 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: `procmacro2_nightly_testing`
       --> src/lib.rs:127:5
        |
    127 |     procmacro2_nightly_testing,
        |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_nightly_testing)");` 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: `proc_macro_span`
       --> src/lib.rs:129:9
        |
    129 |     not(proc_macro_span)
        |         ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(proc_macro_span)");` 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: `wrap_proc_macro`
       --> src/lib.rs:144:7
        |
    144 | #[cfg(wrap_proc_macro)]
        |       ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
       --> src/lib.rs:154:11
        |
    154 | #[cfg(not(wrap_proc_macro))]
        |           ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
       --> src/lib.rs:157:7
        |
    157 | #[cfg(wrap_proc_macro)]
        |       ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `span_locations`
       --> src/lib.rs:160:7
        |
    160 | #[cfg(span_locations)]
        |       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/lib.rs:168:7
        |
    168 | #[cfg(span_locations)]
        |       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `procmacro2_semver_exempt`
       --> src/lib.rs:174:7
        |
    174 | #[cfg(procmacro2_semver_exempt)]
        |       ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `span_locations`
       --> src/lib.rs:177:7
        |
    177 | #[cfg(span_locations)]
        |       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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/lib.rs:255:12
        |
    255 | #[cfg_attr(doc_cfg, doc(cfg(feature = "proc-macro")))]
        |            ^^^^^^^
        |
        = 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: `doc_cfg`
       --> src/lib.rs:263:12
        |
    263 | #[cfg_attr(doc_cfg, doc(cfg(feature = "proc-macro")))]
        |            ^^^^^^^
        |
        = 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: `procmacro2_semver_exempt`
       --> src/lib.rs:341:11
        |
    341 | #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
        |           ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `wrap_proc_macro`
       --> src/lib.rs:341:45
        |
    341 | #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
        |                                             ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `super_unstable`
       --> src/lib.rs:341:63
        |
    341 | #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
        |                                                               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(super_unstable)");` 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: `procmacro2_semver_exempt`
       --> src/lib.rs:349:11
        |
    349 | #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
        |           ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `wrap_proc_macro`
       --> src/lib.rs:349:45
        |
    349 | #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
        |                                             ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `super_unstable`
       --> src/lib.rs:349:63
        |
    349 | #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
        |                                                               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(super_unstable)");` 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: `procmacro2_semver_exempt`
       --> src/lib.rs:382:11
        |
    382 | #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
        |           ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `wrap_proc_macro`
       --> src/lib.rs:382:45
        |
    382 | #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
        |                                             ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `super_unstable`
       --> src/lib.rs:382:63
        |
    382 | #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
        |                                                               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(super_unstable)");` 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: `procmacro2_semver_exempt`
     --> src/marker.rs:9:9
      |
    9 |     all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)),
      |         ^^^^^^^^^^^^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `wrap_proc_macro`
     --> src/marker.rs:9:43
      |
    9 |     all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)),
      |                                           ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `super_unstable`
     --> src/marker.rs:9:61
      |
    9 |     all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)),
      |                                                             ^^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(super_unstable)");` 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: `span_locations`
      --> src/parse.rs:12:11
       |
    12 |     #[cfg(span_locations)]
       |           ^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
      --> src/parse.rs:21:19
       |
    21 |             #[cfg(span_locations)]
       |                   ^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:180:15
        |
    180 |         #[cfg(span_locations)]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:187:23
        |
    187 |                 #[cfg(span_locations)]
        |                       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:193:27
        |
    193 |                 #[cfg(not(span_locations))]
        |                           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:206:19
        |
    206 |             #[cfg(span_locations)]
        |                   ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:220:19
        |
    220 |             #[cfg(span_locations)]
        |                   ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:229:23
        |
    229 |                 #[cfg(span_locations)]
        |                       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:231:23
        |
    231 |                 #[cfg(span_locations)]
        |                       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:242:23
        |
    242 |                 #[cfg(span_locations)]
        |                       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:244:23
        |
    244 |                 #[cfg(span_locations)]
        |                       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:254:15
        |
    254 |     #[cfg(not(span_locations))]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:258:19
        |
    258 |             #[cfg(span_locations)]
        |                   ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:260:19
        |
    260 |             #[cfg(span_locations)]
        |                   ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:914:11
        |
    914 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:918:15
        |
    918 |         #[cfg(span_locations)]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/parse.rs:920:15
        |
    920 |         #[cfg(span_locations)]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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_is_available`
      --> src/detection.rs:26:11
       |
    26 | #[cfg(not(no_is_available))]
       |           ^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_is_available)");` 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_is_available`
      --> src/detection.rs:56:7
       |
    56 | #[cfg(no_is_available)]
       |       ^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(no_is_available)");` 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: `span_locations`
     --> src/fallback.rs:1:7
      |
    1 | #[cfg(span_locations)]
      |       ^^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
     --> src/fallback.rs:6:11
      |
    6 | #[cfg(all(span_locations, not(fuzzing)))]
      |           ^^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `fuzzing`
     --> src/fallback.rs:6:31
      |
    6 | #[cfg(all(span_locations, not(fuzzing)))]
      |                               ^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(fuzzing)");` 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: `span_locations`
     --> src/fallback.rs:8:11
      |
    8 | #[cfg(all(span_locations, not(fuzzing)))]
      |           ^^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `fuzzing`
     --> src/fallback.rs:8:31
      |
    8 | #[cfg(all(span_locations, not(fuzzing)))]
      |                               ^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(fuzzing)");` 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: `span_locations`
      --> src/fallback.rs:10:7
       |
    10 | #[cfg(span_locations)]
       |       ^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
      --> src/fallback.rs:14:7
       |
    14 | #[cfg(span_locations)]
       |       ^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `procmacro2_semver_exempt`
      --> src/fallback.rs:20:7
       |
    20 | #[cfg(procmacro2_semver_exempt)]
       |       ^^^^^^^^^^^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `span_locations`
       --> src/fallback.rs:151:7
        |
    151 | #[cfg(span_locations)]
        |       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:168:11
        |
    168 | #[cfg(not(span_locations))]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `procmacro2_semver_exempt`
       --> src/fallback.rs:302:7
        |
    302 | #[cfg(procmacro2_semver_exempt)]
        |       ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `procmacro2_semver_exempt`
       --> src/fallback.rs:308:7
        |
    308 | #[cfg(procmacro2_semver_exempt)]
        |       ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `procmacro2_semver_exempt`
       --> src/fallback.rs:320:7
        |
    320 | #[cfg(procmacro2_semver_exempt)]
        |       ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `span_locations`
       --> src/fallback.rs:330:11
        |
    330 | #[cfg(all(span_locations, not(fuzzing)))]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `fuzzing`
       --> src/fallback.rs:330:31
        |
    330 | #[cfg(all(span_locations, not(fuzzing)))]
        |                               ^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(fuzzing)");` 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: `span_locations`
       --> src/fallback.rs:344:7
        |
    344 | #[cfg(span_locations)]
        |       ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:350:11
        |
    350 | #[cfg(all(span_locations, not(fuzzing)))]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `fuzzing`
       --> src/fallback.rs:350:31
        |
    350 | #[cfg(all(span_locations, not(fuzzing)))]
        |                               ^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(fuzzing)");` 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: `span_locations`
       --> src/fallback.rs:358:11
        |
    358 | #[cfg(all(span_locations, not(fuzzing)))]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `fuzzing`
       --> src/fallback.rs:358:31
        |
    358 | #[cfg(all(span_locations, not(fuzzing)))]
        |                               ^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(fuzzing)");` 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: `span_locations`
       --> src/fallback.rs:425:11
        |
    425 | #[cfg(all(span_locations, not(fuzzing)))]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `fuzzing`
       --> src/fallback.rs:425:31
        |
    425 | #[cfg(all(span_locations, not(fuzzing)))]
        |                               ^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(fuzzing)");` 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: `span_locations`
       --> src/fallback.rs:440:11
        |
    440 | #[cfg(all(span_locations, not(fuzzing)))]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `fuzzing`
       --> src/fallback.rs:440:31
        |
    440 | #[cfg(all(span_locations, not(fuzzing)))]
        |                               ^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(fuzzing)");` 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: `span_locations`
       --> src/fallback.rs:445:11
        |
    445 | #[cfg(all(span_locations, not(fuzzing)))]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `fuzzing`
       --> src/fallback.rs:445:31
        |
    445 | #[cfg(all(span_locations, not(fuzzing)))]
        |                               ^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(fuzzing)");` 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: `span_locations`
       --> src/fallback.rs:509:11
        |
    509 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:511:11
        |
    511 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `wrap_proc_macro`
      --> src/fallback.rs:26:11
       |
    26 |     #[cfg(wrap_proc_macro)]
       |           ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
      --> src/fallback.rs:33:11
       |
    33 |     #[cfg(wrap_proc_macro)]
       |           ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
      --> src/fallback.rs:80:19
       |
    80 |             #[cfg(wrap_proc_macro)]
       |                   ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
      --> src/fallback.rs:82:23
       |
    82 |             #[cfg(not(wrap_proc_macro))]
       |                       ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
       --> src/fallback.rs:113:19
        |
    113 |             #[cfg(wrap_proc_macro)]
        |                   ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `span_locations`
       --> src/fallback.rs:516:15
        |
    516 |     #[cfg(not(span_locations))]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:521:11
        |
    521 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `procmacro2_semver_exempt`
       --> src/fallback.rs:530:11
        |
    530 |     #[cfg(procmacro2_semver_exempt)]
        |           ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `procmacro2_semver_exempt`
       --> src/fallback.rs:546:11
        |
    546 |     #[cfg(procmacro2_semver_exempt)]
        |           ^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(procmacro2_semver_exempt)");` 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: `span_locations`
       --> src/fallback.rs:561:11
        |
    561 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:576:11
        |
    576 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:589:11
        |
    589 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:602:15
        |
    602 |     #[cfg(not(span_locations))]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:607:11
        |
    607 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:629:15
        |
    629 |     #[cfg(not(span_locations))]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:634:11
        |
    634 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:649:15
        |
    649 |     #[cfg(not(span_locations))]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:654:11
        |
    654 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:662:15
        |
    662 |     #[cfg(not(span_locations))]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:667:11
        |
    667 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:675:11
        |
    675 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:683:15
        |
    683 |         #[cfg(span_locations)]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:686:19
        |
    686 |         #[cfg(not(span_locations))]
        |                   ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:692:11
        |
    692 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:699:13
        |
    699 |     if cfg!(span_locations) {
        |             ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:908:15
        |
    908 |     #[cfg(not(span_locations))]
        |               ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
       --> src/fallback.rs:919:11
        |
    919 |     #[cfg(span_locations)]
        |           ^^^^^^^^^^^^^^
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
        --> src/fallback.rs:1114:19
         |
    1114 |         #[cfg(not(span_locations))]
         |                   ^^^^^^^^^^^^^^
         |
         = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
        --> src/fallback.rs:1120:15
         |
    1120 |         #[cfg(span_locations)]
         |               ^^^^^^^^^^^^^^
         |
         = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
        --> src/fallback.rs:1160:15
         |
    1160 |         #[cfg(span_locations)]
         |               ^^^^^^^^^^^^^^
         |
         = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
        --> src/fallback.rs:1177:27
         |
    1177 |                     #[cfg(span_locations)]
         |                           ^^^^^^^^^^^^^^
         |
         = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
        --> src/fallback.rs:1179:27
         |
    1179 |                     #[cfg(span_locations)]
         |                           ^^^^^^^^^^^^^^
         |
         = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
      --> src/extra.rs:71:7
       |
    71 | #[cfg(span_locations)]
       |       ^^^^^^^^^^^^^^
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `wrap_proc_macro`
      --> src/extra.rs:89:11
       |
    89 |     #[cfg(wrap_proc_macro)]
       |           ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
       |
       = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
       --> src/extra.rs:100:15
        |
    100 |         #[cfg(wrap_proc_macro)]
        |               ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
       --> src/extra.rs:110:19
        |
    110 |         #[cfg(not(wrap_proc_macro))]
        |                   ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
       --> src/extra.rs:122:19
        |
    122 |             #[cfg(wrap_proc_macro)]
        |                   ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
       --> src/extra.rs:131:19
        |
    131 |             #[cfg(wrap_proc_macro)]
        |                   ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `wrap_proc_macro`
       --> src/extra.rs:140:19
        |
    140 |             #[cfg(wrap_proc_macro)]
        |                   ^^^^^^^^^^^^^^^ help: there is a config with a similar name: `proc_macro`
        |
        = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(wrap_proc_macro)");` 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: `span_locations`
     --> src/wrapper.rs:2:7
      |
    2 | #[cfg(span_locations)]
      |       ^^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `span_locations`
     --> src/wrapper.rs:6:7
      |
    6 | #[cfg(span_locations)]
      |       ^^^^^^^^^^^^^^
      |
      = help: consider using a Cargo feature instead or adding `println!("cargo::rustc-check-cfg=cfg(span_locations)");` 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: `super_unstable`…

Author: dtolnay

build.rs

@@ -34,6 +34,8 @@
 //     macro API and catching a panic if it isn't available. Enabled on Rust
 //     1.57+.
 
+#![allow(unexpected_cfgs)]
+
 use std::env;
 use std::ffi::OsString;
 use std::iter;
@@ -44,6 +46,23 @@ use std::str;
 fn main() {
     let rustc = rustc_minor_version().unwrap_or(u32::MAX);
 
+    if rustc >= 80 {
+        println!("cargo:rustc-check-cfg=cfg(doc_cfg)");
+        println!("cargo:rustc-check-cfg=cfg(fuzzing)");
+        println!("cargo:rustc-check-cfg=cfg(nightly)");
+        println!("cargo:rustc-check-cfg=cfg(no_is_available)");
+        println!("cargo:rustc-check-cfg=cfg(no_literal_byte_character)");
+        println!("cargo:rustc-check-cfg=cfg(no_literal_c_string)");
+        println!("cargo:rustc-check-cfg=cfg(no_source_text)");
+        println!("cargo:rustc-check-cfg=cfg(proc_macro_span)");
+        println!("cargo:rustc-check-cfg=cfg(procmacro2_backtrace)");
+        println!("cargo:rustc-check-cfg=cfg(procmacro2_nightly_testing)");
+        println!("cargo:rustc-check-cfg=cfg(procmacro2_semver_exempt)");
+        println!("cargo:rustc-check-cfg=cfg(span_locations)");
+        println!("cargo:rustc-check-cfg=cfg(super_unstable)");
+        println!("cargo:rustc-check-cfg=cfg(wrap_proc_macro)");
+    }
+
     let docs_rs = env::var_os("DOCS_RS").is_some();
     let semver_exempt = cfg!(procmacro2_semver_exempt) || docs_rs;
     if semver_exempt {