Unresolved import from imported crates.io crate

[stackoverflow010]

I am trying to use the opencv crate with the dnn module. I have compiled opencv with DNN and verified that all the shared libraries exist. If I try to build the following code

use opencv::{
    dnn,
    core::{Vector},
};

fn main() {
    let a: Vector<i32> = Vector::<i32>::new();
    println!("OPENCV TEST");
}

I receive the error

error[E0432]: unresolved import `opencv::dnn`
 --> src/main.rs:2:5
  |
2 |     dnn,
  |     ^^^ no `dnn` in the root

For more information about this error, try `rustc --explain E0432`.

My Cargo.toml

[package]
name = "foobar"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
opencv = "0.80.0"

At first I thought this issue was somehow related to rust not being able to find some shared library (e.g. libcudnn.so), but (a) that should be a runtime concern, and (b) this error seems to be suggesting that the module itself is not found. I'm a bit unclear on what is going on here, and I think I'm doing something foolish.

I have:

1. confirmed opencv was built with dnn and that all the libraries exist
2. the linker path contains the relevant library paths (which still should just be a runtime concern)
3. the crate does not specify the need to gate the "dnn" module with a feature flag
4. Cargo.toml specifies rust 2021

If anyone can suggest some debugging tips, that would be helpful. Thanks.

[nerditation]

it seems the build script didn't generate rust bindings for the specific module. did you check the output of the crate build script? it should be located at "target/{debug or release}/{crate}-{hash}/output", maybe there's some logging information to help you figure out what's actually happened.