Unnecessary library file was generated (copied) into `priv/native/`

[takasehideki]

We are developing a library called Zenohex using Rustler. We are deeply grateful for providing such an excellent package as Rustler!!
https://github.com/biyooon-ex/zenohex

While using the latest version, Rustler v0.37.1, I noticed that a library file rustls_platform_verifier.so that seemed unnecessary was being generated (copied) into the native/priv/. The only file required should be zenohex_nif.so.
I confirmed that rustls_platform_verifier.so was not generated in the previous v0.36.2 version. I guess that something changed due to recent code modifications in compiler.ex.
rustler-0.36.2...rustler-0.37.1#diff-aea852ba0a1ff20d4a5eab3df8c59e3fc4e91560f8a0e07d131e1ca2ca600127

I am continuing the investigation, but I have not yet found the exact cause and solution. So I decided to create this issue to share our situation at first.

environment

• macOS and Linux (occurred in both)
• Elixir 1.18.4-otp-27
• Erlang/OTP 27.3.4.2
• Rust 1.89.0
• Rustler 0.37.1
• Rustler_precompiled 0.8.3

How to reproduce

$ git clone https://github.com/biyooon-ex/zenohex
$ cd zenohex
$ mix deps.get && mix compile
<skip>
==> rustler_precompiled
Compiling 4 files (.ex)
Generated rustler_precompiled app
==> zenohex
Compiling 22 files (.ex)
Compiling crate zenohex_nif in release mode (native/zenohex_nif)
Copying /<workdir>/zenohex/native/zenohex_nif/target/release/deps/librustls_platform_verifier-7a7678b64ab91b26.dylib to priv/native/rustls_platform_verifier.so
Copying /<workdir>/zenohex/native/zenohex_nif/target/release/libzenohex_nif.dylib to priv/native/zenohex_nif.so
Generated zenohex app

$ ls priv/native
rustls_platform_verifier.so* zenohex_nif.so*

[filmor]

The relevant change from 0.36 to 0.37 is #691. I refactored the build step to get the artifacts from the JSON messages that cargo produces at build time. This is necessary to be able to collect dynamically linked dependencies.

In your concrete case, the issue is that you depend on https://github.com/rustls/rustls-platform-verifier/ via quinn. This library has the following output setting:

https://github.com/rustls/rustls-platform-verifier/blob/9c727a99783cc78674dad195908250d54b33f631/rustls-platform-verifier/Cargo.toml#L12-L16

This means that it will always build a cdylib, while your library will actually link it directly via the (also built) rlib.

There doesn't seem to be a way to override this.

I will see if this situation can be detected from the compiler messages and create an upstream PR to only build the cdylib when necessary.

[filmor]

This has been fixed upstream. I don't think there is anything additional we have to do here.

[takasehideki]

Thank you so much for the great work!! ❤️
After updating rustls-platform-verifier to version 0.6.2 in our library, we confirmed that this issue no longer occurs!