Rust: Support external crates

[zeenix]

I was told that support of Rust was experimental so I can expect hickups and that's understandable but currently it seems external crates are not supported. Since you can't really do much in Rust without external crates, it basically means that Meson doesn't really support Rust. IMO until this issue is addressed in some way, support for Rust shouldn't be advertised at all.

[TingPing]

Correct me if I am wrong but Cargo simply just builds all dependencies and there is no concept of external dependencies (ala pkgconfig) right? Does Rust even have any standard directory to install shared libraries? If so we should support rust.find_library().

Otherwise just like Cargo to build all dependencies then all dependencies have to use Meson.

[tp-m]

I think what's needed is more something that does what Cargo does - downloads crates as per Cargo.toml and Cargo.lock and builds them / links them in as needed. This would be really powerful, esp. for mixed C/Rust projects.

[TingPing]

So we either:

• Re-implement Cargo
• Simply call Cargo making the Meson integration worthless

[zeenix]

@TingPing typically they just do static linking in Rust currently. cargo will simply download, build all deps and then take care of linking your binaries.

[zeenix]

@TingPing yeah but please keep in mind that this is useful for projects that will be a mix of Rust and C (or some other language for which meson is a good option).

[TingPing]

I realize its valuable but its not a realistic thing we can support. It is like wanting Meson to support building autotools projects. Cargo is its own independent and incompatible build system.

[zeenix]

@TingPing I would completely understand if you decide not to support this in meson but then either Rust support shouldn't be advertised at all or this limitation should be explicitly specified. As I mentioned, without this, Rust support is mostly useless.

[TingPing]

We have (basic) Rust support, we don't have Cargo support. It is sad that the Rust community only cares about Cargo and does not install shared libraries or have any tooling to collect information about installed libraries.

[tp-m]

While it is certainly "independent", It's not clear to me that it really is "incompatible". I see crates more like a special kind of subproject.

[zeenix]

@TingPing yeah, i know but fact remains that the support is useless for most uses so really nothing to advertise. I fully agree about Rust folks not doing things the standard way.

[TingPing]

I wasn't aware Meson was 'advertising' rust support other than it being documented. It is certainly basic.

[zeenix]

IMO basic isn't the correct term. Even the simplest of Rust projects will depend on external crates and meson can't handle those.

[tp-m]

I'd say let's focus on what a possible useful solution/implementation would require or could look like, and move the whole what should be advertised or not or whether something useful can be done without this feature or not thing elsewhere :)