False positive on unused_import and dead_code

[shnewto]

Summary

hello! I love clippy, don't know what I'd do without it 😄 but I caught a couple false positives I'd like to share. thanks for taking a look!

reproducer

link to source effected https://github.com/shnewto/edges/blob/7e2566e73a6fd0bafc4756e07293d5264556391d/src/edges.rs#L244-L321

here it is too, notice the #[allow(dead_code)] and #[allow(unused_imports)]

impl fmt::Debug for Edges {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        #[derive(Debug)]
        #[allow(dead_code)]
        struct EdgesDisplay {
            raw: Vec<Vec<Vec2>>,
            translated: Vec<Vec<Vec2>>,
        }


        let edges_display = EdgesDisplay {
            raw: self.image_edges(false),
            translated: self.image_edges(false),
        };
        write!(f, "{:#?}", edges_display)
    }
}


#[cfg(feature = "bevy")]
mod tests {
    #[allow(unused_imports)]
    use super::Edges;
    #[allow(unused_imports)]
    use bevy::{prelude::Image, render::texture::ImageType};
    #[allow(unused_imports)]
    use std::path::Path;


    #[test]
    fn same_image_same_edges() {
        let dynamic_image = image::open(Path::new("assets/car.png")).unwrap();
        let dynamic_edges = Edges::from(dynamic_image);


        let bevy_image = Image::from_buffer(
            include_bytes!("../assets/car.png"), // buffer
            ImageType::Extension("png"),
            Default::default(),
            true, //
            Default::default(),
            Default::default(),
        )
        .unwrap();
        let bevy_edges = Edges::from(bevy_image);


        assert_eq!(
            dynamic_edges.single_image_edge_raw(),
            bevy_edges.single_image_edge_raw()
        );
        assert_eq!(
            dynamic_edges.single_image_edge_translated(),
            bevy_edges.single_image_edge_translated()
        );
    }


    #[test]
    fn same_images_same_edges() {
        let dynamic_image = image::open(Path::new("assets/boulders.png")).unwrap();
        let dynamic_edges = Edges::from(dynamic_image);


        let bevy_image = Image::from_buffer(
            include_bytes!("../assets/boulders.png"), // buffer
            ImageType::Extension("png"),
            Default::default(),
            true, //
            Default::default(),
            Default::default(),
        )
        .unwrap();
        let bevy_edges = Edges::from(bevy_image);


        assert_eq!(
            dynamic_edges.multi_image_edges_raw(),
            bevy_edges.multi_image_edges_raw()
        );
        assert_eq!(
            dynamic_edges.multi_image_edge_translated(),
            bevy_edges.multi_image_edge_translated()
        );
    }
}

version

rustup --version

rustup 1.26.0 (5af9b9484 2023-04-05)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.78.0-nightly (516b6162a 2024-03-03)`

rustc -Vv

rustc 1.78.0-nightly (516b6162a 2024-03-03)
binary: rustc
commit-hash: 516b6162a2ea8e66678c09e8243ebd83e4b8eeea
commit-date: 2024-03-03
host: x86_64-apple-darwin
release: 1.78.0-nightly
LLVM version: 18.1.0

output

clippy output after cargo clippy --all-features --all-targets (and just running cargo clippy without args)

warning: unused import: `super::Edges`
   --> src/edges.rs:262:9
    |
262 |     use super::Edges;
    |         ^^^^^^^^^^^^
    |
    = note: `#[warn(unused_imports)]` on by default

warning: unused imports: `prelude::Image`, `render::texture::ImageType`
   --> src/edges.rs:263:16
    |
263 |     use bevy::{prelude::Image, render::texture::ImageType};
    |                ^^^^^^^^^^^^^^  ^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: unused import: `std::path::Path`
   --> src/edges.rs:264:9
    |
264 |     use std::path::Path;
    |         ^^^^^^^^^^^^^^^

warning: fields `raw` and `translated` are never read
   --> src/edges.rs:248:13
    |
247 |         struct EdgesDisplay {
    |                ------------ fields in this struct
248 |             raw: Vec<Vec<Vec2>>,
    |             ^^^
249 |             translated: Vec<Vec<Vec2>>,
    |             ^^^^^^^^^^
    |
    = note: `EdgesDisplay` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis
    = note: `#[warn(dead_code)]` on by default

warning: `edges` (lib) generated 4 warnings (run `cargo clippy --fix --lib -p edges` to apply 3 suggestions)
warning: `edges` (lib test) generated 1 warning (1 duplicate)

compile errors after taking clippy's suggestion in the mod and running cargo build --features bevy

error[E0560]: struct `EdgesDisplay` has no field named `raw`
   --> src/edges.rs:251:13
    |
251 |             raw: self.image_edges(false),
    |             ^^^ `EdgesDisplay` does not have this field
    |
    = note: all struct fields are already assigned

error[E0560]: struct `EdgesDisplay` has no field named `translated`
   --> src/edges.rs:252:13
    |
252 |             translated: self.image_edges(false),
    |             ^^^^^^^^^^ `EdgesDisplay` does not have this field
    |
    = note: all struct fields are already assigned

For more information about this error, try `rustc --explain E0560`.
error: could not compile `edges` (lib) due to 2 previous errors

compile errors after taking clippy's suggestion in the tests and running cargo test --features bevy

error[E0433]: failed to resolve: use of undeclared type `Path`
   --> src/edges.rs:265:41
    |
265 |         let dynamic_image = image::open(Path::new("assets/car.png")).unwrap();
    |                                         ^^^^ use of undeclared type `Path`
    |
help: consider importing this struct
    |
263 +     use std::path::Path;
    |

error[E0433]: failed to resolve: use of undeclared type `Edges`
   --> src/edges.rs:266:29
    |
266 |         let dynamic_edges = Edges::from(dynamic_image);
    |                             ^^^^^ use of undeclared type `Edges`
    |
help: consider importing one of these items
    |
263 +     use bevy::ecs::archetype::Edges;
    |
263 +     use bevy::render::render_graph::Edges;
    |
263 +     use crate::Edges;
    |

error[E0433]: failed to resolve: use of undeclared type `Image`
   --> src/edges.rs:268:26
    |
268 |         let bevy_image = Image::from_buffer(
    |                          ^^^^^ use of undeclared type `Image`
    |
help: consider importing this struct
    |
263 +     use bevy::render::texture::Image;
    |

error[E0433]: failed to resolve: use of undeclared type `ImageType`
   --> src/edges.rs:270:13
    |
270 |             ImageType::Extension("png"),
    |             ^^^^^^^^^ use of undeclared type `ImageType`
    |
help: consider importing this enum
    |
263 +     use bevy::render::texture::ImageType;
    |

error[E0433]: failed to resolve: use of undeclared type `Edges`
   --> src/edges.rs:277:26
    |
277 |         let bevy_edges = Edges::from(bevy_image);
    |                          ^^^^^ use of undeclared type `Edges`
    |
help: consider importing one of these items
    |
263 +     use bevy::ecs::archetype::Edges;
    |
263 +     use bevy::render::render_graph::Edges;
    |
263 +     use crate::Edges;
    |

error[E0433]: failed to resolve: use of undeclared type `Path`
   --> src/edges.rs:291:41
    |
291 |         let dynamic_image = image::open(Path::new("assets/boulders.png")).unwrap();
    |                                         ^^^^ use of undeclared type `Path`
    |
help: consider importing this struct
    |
263 +     use std::path::Path;
    |

error[E0433]: failed to resolve: use of undeclared type `Edges`
   --> src/edges.rs:292:29
    |
292 |         let dynamic_edges = Edges::from(dynamic_image);
    |                             ^^^^^ use of undeclared type `Edges`
    |
help: consider importing one of these items
    |
263 +     use bevy::ecs::archetype::Edges;
    |
263 +     use bevy::render::render_graph::Edges;
    |
263 +     use crate::Edges;
    |

error[E0433]: failed to resolve: use of undeclared type `Image`
   --> src/edges.rs:294:26
    |
294 |         let bevy_image = Image::from_buffer(
    |                          ^^^^^ use of undeclared type `Image`
    |
help: consider importing this struct
    |
263 +     use bevy::render::texture::Image;
    |

error[E0433]: failed to resolve: use of undeclared type `ImageType`
   --> src/edges.rs:296:13
    |
296 |             ImageType::Extension("png"),
    |             ^^^^^^^^^ use of undeclared type `ImageType`
    |
help: consider importing this enum
    |
263 +     use bevy::render::texture::ImageType;
    |

error[E0433]: failed to resolve: use of undeclared type `Edges`
   --> src/edges.rs:303:26
    |
303 |         let bevy_edges = Edges::from(bevy_image);
    |                          ^^^^^ use of undeclared type `Edges`
    |
help: consider importing one of these items
    |
263 +     use bevy::ecs::archetype::Edges;
    |
263 +     use bevy::render::render_graph::Edges;
    |
263 +     use crate::Edges;
    |

For more information about this error, try `rustc --explain E0433`.

Again, thanks for taking a look. And thanks for all your incredible work!

Lint Name

unused_imports, dead_code

[shnewto]

well okay, the mod test unused imports is not the false positive I thought! I was missing #[cfg(test)] over mod test, i.e.

#[cfg(feature = "bevy")]
#[cfg(test)]
mod tests {

that solves that one, but the dead_code lint in the Debug trait i think is still a false positive

[shnewto]

another note, it was suggested to me that clippy is probably right regarding the struct fields in the Debug trait too, that writing/printing the struct doesn't qualify as reading the fields? I'm okay with that I think 🤔

both of these scenarios though do feel like they require more technical rust knowledge to understand than I'm used to needing with clippy.

and if nothing else running cargo clippy --fix --all-features --all-targets breaks working code 😅

[Alexendoo]

These are lints from rustc rather than Clippy, Debug being excluded from dead code analysis is intentional so it may stay that #[allow(dead_code)] is required, but there's a rustc issue here rust-lang/rust#123068