Unexpected cfg condition name: mac_ & ios_framework

[e5f6bd]

When I compile sdl2-sys crate with the latest stable Rust, I get this kind of error message:

warning: unexpected `cfg` condition name: `ios_framework`
   --> sdl2-sys\build.rs:340:46
    |
340 |                 let use_framework = cfg!(any(ios_framework, feature = "use_ios_framework"));
    |                                              ^^^^^^^^^^^^^
    |
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
             unexpected_cfgs = { level = "warn", check-cfg = ['cfg(ios_framework)'] }
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

Entire warnings

warning: unexpected `cfg` condition name: `mac_framework`
   --> sdl2-sys\build.rs:333:46
    |
333 |                 let use_framework = cfg!(any(mac_framework, feature = "use_mac_framework"));
    |                                              ^^^^^^^^^^^^^
    |
    = 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`, and `windows`
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
             unexpected_cfgs = { level = "warn", check-cfg = ['cfg(mac_framework)'] }
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

warning: unexpected `cfg` condition name: `ios_framework`
   --> sdl2-sys\build.rs:340:46
    |
340 |                 let use_framework = cfg!(any(ios_framework, feature = "use_ios_framework"));
    |                                              ^^^^^^^^^^^^^
    |
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
             unexpected_cfgs = { level = "warn", check-cfg = ['cfg(ios_framework)'] }
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

warning: unexpected `cfg` condition name: `mac_framework`
   --> sdl2-sys\build.rs:357:46
    |
357 |                 let use_framework = cfg!(any(mac_framework, feature = "use_mac_framework"));
    |                                              ^^^^^^^^^^^^^
    |
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
             unexpected_cfgs = { level = "warn", check-cfg = ['cfg(mac_framework)'] }
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

warning: unexpected `cfg` condition name: `ios_framework`
   --> sdl2-sys\build.rs:364:46
    |
364 |                 let use_framework = cfg!(any(ios_framework, feature = "use_ios_framework"));
    |                                              ^^^^^^^^^^^^^
    |
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
             unexpected_cfgs = { level = "warn", check-cfg = ['cfg(ios_framework)'] }
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

warning: unexpected `cfg` condition name: `mac_framework`
   --> sdl2-sys\build.rs:381:46
    |
381 |                 let use_framework = cfg!(any(mac_framework, feature = "use_mac_framework"));
    |                                              ^^^^^^^^^^^^^
    |
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
             unexpected_cfgs = { level = "warn", check-cfg = ['cfg(mac_framework)'] }
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

warning: unexpected `cfg` condition name: `ios_framework`
   --> sdl2-sys\build.rs:388:46
    |
388 |                 let use_framework = cfg!(any(ios_framework, feature = "use_ios_framework"));
    |                                              ^^^^^^^^^^^^^
    |
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
             unexpected_cfgs = { level = "warn", check-cfg = ['cfg(ios_framework)'] }
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

warning: unexpected `cfg` condition name: `mac_framework`
   --> sdl2-sys\build.rs:405:46
    |
405 |                 let use_framework = cfg!(any(mac_framework, feature = "use_mac_framework"));
    |                                              ^^^^^^^^^^^^^
    |
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
             unexpected_cfgs = { level = "warn", check-cfg = ['cfg(mac_framework)'] }
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

warning: unexpected `cfg` condition name: `ios_framework`
   --> sdl2-sys\build.rs:412:46
    |
412 |                 let use_framework = cfg!(any(ios_framework, feature = "use_ios_framework"));
    |                                              ^^^^^^^^^^^^^
    |
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
             unexpected_cfgs = { level = "warn", check-cfg = ['cfg(ios_framework)'] }
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration

warning: `sdl2-sys` (build script) generated 8 warnings

Is there any reason of using a custom cfg attributes, ios_framework and mac_framework? Or is it just a reminicent of good old code that is never used right now? It seems these attributes started to be used at least before 2017 ... (as in b3ee9b2)

[e5f6bd]

Well, I found my browser has a tab showing #588, so it seems I found this issue but forget to further investigate. So I think this attribute is checked intentionally to support --cfg mac_framework. Then I think we should specify lints.rust.unexpected_cfgs.check-cfg as suggested.