Cannot compile when default-features are disabled (false)

[FirelightFlagboy]

Steps to reproduce

cargo new --lib foo
cd foo
cargo add flate2@1.0.26 --no-default-features
cargo check # or 'cargo build'

The error log I'm getting

cargo checks output

   Compiling flate2 v1.0.26
error[E0433]: failed to resolve: use of undeclared crate or module `miniz_oxide`
 --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:6:5
  |
6 | use miniz_oxide::deflate::core::CompressorOxide;
  |     ^^^^^^^^^^^ use of undeclared crate or module `miniz_oxide`

error[E0433]: failed to resolve: use of undeclared crate or module `miniz_oxide`
 --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:7:5
  |
7 | use miniz_oxide::inflate::stream::InflateState;
  |     ^^^^^^^^^^^ use of undeclared crate or module `miniz_oxide`

error[E0432]: unresolved imports `miniz_oxide`, `miniz_oxide::deflate::core::CompressorOxide`, `miniz_oxide::inflate::stream::InflateState`, `crate::ffi::Backend`, `crate::ffi::Deflate`, `crate::ffi::DeflateBackend`, `crate::ffi::ErrorMessage`, `crate::ffi::Inflate`, `crate::ffi::InflateBackend`
 --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:6:5
  |
6 | use miniz_oxide::deflate::core::CompressorOxide;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
7 | use miniz_oxide::inflate::stream::InflateState;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
8 | pub use miniz_oxide::*;
  |         ^^^^^^^^^^^ use of undeclared crate or module `miniz_oxide`
  |
 ::: /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:6:24
  |
6 | use crate::ffi::{self, Backend, Deflate, DeflateBackend, ErrorMessage, Inflate, InflateBackend};
  |                        ^^^^^^^  ^^^^^^^  ^^^^^^^^^^^^^^  ^^^^^^^^^^^^  ^^^^^^^  ^^^^^^^^^^^^^^

error[E0433]: failed to resolve: use of undeclared type `MZFlush`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:10:32
   |
10 | pub const MZ_NO_FLUSH: isize = MZFlush::None as isize;
   |                                ^^^^^^^ use of undeclared type `MZFlush`

error[E0433]: failed to resolve: use of undeclared type `MZFlush`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:11:37
   |
11 | pub const MZ_PARTIAL_FLUSH: isize = MZFlush::Partial as isize;
   |                                     ^^^^^^^ use of undeclared type `MZFlush`

error[E0433]: failed to resolve: use of undeclared type `MZFlush`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:12:34
   |
12 | pub const MZ_SYNC_FLUSH: isize = MZFlush::Sync as isize;
   |                                  ^^^^^^^ use of undeclared type `MZFlush`

error[E0433]: failed to resolve: use of undeclared type `MZFlush`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:13:34
   |
13 | pub const MZ_FULL_FLUSH: isize = MZFlush::Full as isize;
   |                                  ^^^^^^^ use of undeclared type `MZFlush`

error[E0433]: failed to resolve: use of undeclared type `MZFlush`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:14:30
   |
14 | pub const MZ_FINISH: isize = MZFlush::Finish as isize;
   |                              ^^^^^^^ use of undeclared type `MZFlush`

error[E0433]: failed to resolve: use of undeclared type `DataFormat`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:31:9
   |
31 |         DataFormat::Zlib
   |         ^^^^^^^^^^ use of undeclared type `DataFormat`

error[E0433]: failed to resolve: use of undeclared type `DataFormat`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:33:9
   |
33 |         DataFormat::Raw
   |         ^^^^^^^^^^ use of undeclared type `DataFormat`

error[E0433]: failed to resolve: use of undeclared crate or module `inflate`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:72:19
   |
72 |         let res = inflate::stream::inflate(&mut self.inner, input, output, flush);
   |                   ^^^^^^^ use of undeclared crate or module `inflate`

error[E0433]: failed to resolve: use of undeclared type `MZStatus`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:78:17
   |
78 |                 MZStatus::Ok => Ok(Status::Ok),
   |                 ^^^^^^^^ use of undeclared type `MZStatus`

error[E0433]: failed to resolve: use of undeclared type `MZStatus`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:79:17
   |
79 |                 MZStatus::StreamEnd => Ok(Status::StreamEnd),
   |                 ^^^^^^^^ use of undeclared type `MZStatus`

error[E0433]: failed to resolve: use of undeclared type `MZStatus`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:80:17
   |
80 |                 MZStatus::NeedDict => {
   |                 ^^^^^^^^ use of undeclared type `MZStatus`

error[E0433]: failed to resolve: use of undeclared type `MZError`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:85:17
   |
85 |                 MZError::Buf => Ok(Status::BufError),
   |                 ^^^^^^^ use of undeclared type `MZError`

error[E0433]: failed to resolve: use of undeclared crate or module `deflate`
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:149:19
    |
149 |         let res = deflate::stream::deflate(&mut self.inner, input, output, flush);
    |                   ^^^^^^^ use of undeclared crate or module `deflate`

error[E0433]: failed to resolve: use of undeclared type `MZStatus`
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:155:17
    |
155 |                 MZStatus::Ok => Ok(Status::Ok),
    |                 ^^^^^^^^ use of undeclared type `MZStatus`

error[E0433]: failed to resolve: use of undeclared type `MZStatus`
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:156:17
    |
156 |                 MZStatus::StreamEnd => Ok(Status::StreamEnd),
    |                 ^^^^^^^^ use of undeclared type `MZStatus`

error[E0433]: failed to resolve: use of undeclared type `MZStatus`
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:157:17
    |
157 |                 MZStatus::NeedDict => mem::compress_failed(ErrorMessage),
    |                 ^^^^^^^^ use of undeclared type `MZStatus`

error[E0433]: failed to resolve: use of undeclared type `MZError`
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:160:17
    |
160 |                 MZError::Buf => Ok(Status::BufError),
    |                 ^^^^^^^ use of undeclared type `MZError`

error[E0412]: cannot find type `DataFormat` in this scope
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:29:43
   |
29 | fn format_from_bool(zlib_header: bool) -> DataFormat {
   |                                           ^^^^^^^^^^ not found in this scope

error[E0425]: cannot find value `MZ_DEFAULT_WINDOW_BITS` in module `ffi`
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:198:59
    |
198 |             inner: Deflate::make(level, zlib_header, ffi::MZ_DEFAULT_WINDOW_BITS as u8),
    |                                                           ^^^^^^^^^^^^^^^^^^^^^^ not found in `ffi`

error[E0425]: cannot find value `MZ_DEFAULT_WINDOW_BITS` in module `ffi`
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:368:52
    |
368 |             inner: Inflate::make(zlib_header, ffi::MZ_DEFAULT_WINDOW_BITS as u8),
    |                                                    ^^^^^^^^^^^^^^^^^^^^^^ not found in `ffi`

note: erroneous constant used
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:51:12
   |
51 |     None = ffi::MZ_NO_FLUSH as isize,
   |            ^^^^^^^^^^^^^^^^

note: erroneous constant used
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:60:12
   |
60 |     Sync = ffi::MZ_SYNC_FLUSH as isize,
   |            ^^^^^^^^^^^^^^^^^^

note: erroneous constant used
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:70:15
   |
70 |     Partial = ffi::MZ_PARTIAL_FLUSH as isize,
   |               ^^^^^^^^^^^^^^^^^^^^^

note: erroneous constant used
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:77:12
   |
77 |     Full = ffi::MZ_FULL_FLUSH as isize,
   |            ^^^^^^^^^^^^^^^^^^

note: erroneous constant used
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:83:14
   |
83 |     Finish = ffi::MZ_FINISH as isize,
   |              ^^^^^^^^^^^^^^

note: erroneous constant used
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:94:12
   |
94 |     None = ffi::MZ_NO_FLUSH as isize,
   |            ^^^^^^^^^^^^^^^^

note: erroneous constant used
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:103:12
    |
103 |     Sync = ffi::MZ_SYNC_FLUSH as isize,
    |            ^^^^^^^^^^^^^^^^^^

note: erroneous constant used
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/mem.rs:109:14
    |
109 |     Finish = ffi::MZ_FINISH as isize,
    |              ^^^^^^^^^^^^^^

error[E0433]: failed to resolve: use of undeclared type `MZFlush`
  --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:70:21
   |
70 |         let flush = MZFlush::new(flush as i32).unwrap();
   |                     ^^^^^^^ use of undeclared type `MZFlush`

error[E0433]: failed to resolve: use of undeclared type `MZFlush`
   --> /home/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/flate2-1.0.26/src/ffi/rust.rs:148:21
    |
148 |         let flush = MZFlush::new(flush as i32).unwrap();
    |                     ^^^^^^^ use of undeclared type `MZFlush`

Some errors have detailed explanations: E0412, E0425, E0432, E0433.
For more information about an error, try `rustc --explain E0412`.
error: could not compile `flate2` (lib) due to 25 previous errors

Expected behavior

Either:

• the feature rust_backend should not be a feature since the code expect it

• An early compile error indicating that I must choose a proper backend

  #[cfg(not(any(feature = "rust_backend", feature = "zlib", feature = "zlib-ng", feature = "zlib-ng-compat")))]
  compile_error!("You need to choose a backend between: rust_backend, zlib, zlib-ng and zlib-ng-compat");

[Byron]

Thanks for reporting and for researching solutions.

I tried to go with variant 2) and tried to reduce the amount of other errors shown to less than a page so folks have a chance to see the specialised message. It would be truly great if compilation could abort immediately when a compile_error is seen.