Static linking of OpenSSL when using sqlx and sqlx-macros

[emk]

Thank you for maintaining the Rust OpenSSL crates!

I'm the maintainer of rust-musl-builder, a Docker image used for building static Rust binaries that include openssl and diesel. I'm currently working to add support for sqlx, and I've run into an interesting challenge: launchbadge/sqlx#670

In a nutshell, sqlx includes an sqlx-macros package that connects to the database at compile-time. It does this to validate prepared statements, supporting syntax checking of SQL, and type-checking of prepared statement arguments. But this means that it winds up linking against openssl-sys twice:

1. sqlx-macros links against openssl-sys and glibc at compile time. Rust insists that procedural macros are always shared libraries.
2. sqlx links against openssl-sys and muslc-libc in the final binary, which is static.

Unfortunately, this means that we need to keep track of two versions of OpenSSL: a shared glibc version for macros, and a static musl-libc version for the final binary. And OPENSSL_STATIC doesn't offer enough control over openssl-sys to make this work.

I'm not sure what the ideal fix is here. I've proposed several solutions to the sqlx maintainers in launchbadge/sqlx#670, and I don't even know if a fix is possible at the level of sqlx. So I'm very much open to suggestions. If you do think that this problem is best fixed at the openssl-sys level, please let me know, and I'll try to figure out the details and prepare a PR.

Once again, thank you for maintaining the openssl crate! It has brought a lot of value to Rust community.

[sfackler]

All of the environment variables can be prefixed with the target architecture, so you can set X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_STATIC=1 which will only apply to the build for sqlx, not sqlx-macros: https://docs.rs/openssl/0.10.30/openssl/#manual.

[emk]

Thank you! Preliminary testing suggests that X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_STATIC=1 works.

I will be updating rust-musl-builder accordingly and re-running the full test test suite. If it works, I'll close this issue. And with any luck, anybody using rust-musl-builder should be able to use sqlx (or other libraries using openssl-sys at compile time) without issues.

[emk]

I have updated rust-musl-builder to set:

X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_DIR=/usr/local/musl/
X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_STATIC=1

This makes sqlx work very nicely, out of the box. It's still necessary to use cargo sqlx prepare to avoid connecting to a database at buid time.

Thank you very much for your help figuring this out!

[Rizary]

@emk sorry for tagging you, but I came across this issue when trying to build static rust binary. May I ask whether you have an example of doing cargo sqlx prepare or not in your repo? I couldn't find where should I run the command.