Unable to make crate examples

[zmitchell]

I've made a library crate using maturin and I'd like to make some examples so that I can have a binary to profile with stuff like flamegraph. This is my project structure:

ham2spec/
    src/
        lib.rs
    examples/
        my_example.rs
    Cargo.toml
    pyproject.toml

This is (a simplified version of) what my example looks like:

use ham2spec::some_func;

fn main() {
    let foo = some_func();
}

I also have the example listed in my Cargo.toml:

[[example]]
name = "my_example"
path = "examples/my_example.rs"

I'm getting the error unresolved import 'ham2spec'. It's my understanding that directly adding crates via extern crate is not needed with recent versions of Rust. I added extern crate ham2spec anyway and I get the error can't find crate for 'ham2spec'.

So, what am I doing wrong?

[adamreichold]

Can you post the full example somewhere? Or at least the content of Cargo.toml?

[adamreichold]

I am not completely sure, but I think

crate-type = ["cdylib"]

is the culprit as it means only a shared library is built whereas the example needs a Rust library to link against, i.e.

crate-type = ["rlib", "cdylib"]

[zmitchell]

Ok so adding "rlib" allows the example to pick up my crate, but now I'm getting linker errors when I run cargo run --example stick_spectrum. If I remove the "cdylib" the linker errors go away and the example runs properly. So now my question is how do I use rlib when I want to run examples and cdylib when I'm building wheels?

[mejrs]

I think this is one of those things that's just not really supported in cargo examples. It's a nice feature but it doesn't feel very polished.

We benchmark some of our own examples when running pyo3's CI. Can you try what we do?

[zmitchell]

I really just needed a binary to run a profiler on, so switching crate-type when I need to do that works well enough at the moment. Thanks for your help!

[adamreichold]

IIRC, for this to work out, you need to make the extension-module feature optional, i.e. instead of

pyo3 = { version = "0.15.1", features = ["extension-module"] }

do

[features]
default = ["extension-module"]
extension-module = ["pyo3/extension-module"]

[dependencies]
pyo3 = "0.15.1"

and run your example with

> cargo run --no-default-features --example stick_spectrum