Is there a way to re-use Servo's Cargo.lock and rustc version from a third party project?

[paulrouget]

This issue is part of an effort to improve Servo's embedding story. See https://github.com/paulrouget/servoshell/projects/2

Using libservo in another project requires copying Cargo.lock from Servo, and also make sure we use the same rustc version.

Is there a Cargo mechanism that would improve this?

[paulrouget]

/cc @metajack

[metajack]

cc @aturon

I think rustc and cargo can be solved by rust-lang/rustup#460. I seem to recall there was agreement to do this, but noone had time to implement it yet. The bugs paint a more complicated picture.

As for copying Cargo.lock (or inheriting or whatever) for a library dependency, this is a non-goal of Cargo, but it seems like we need some kind of tooling for this.

[tschneidereit]

rust-lang/rustup#460 is resolved, so that should only leave the Cargo.lock issue to deal with. @paulrouget Can you confirm that we can now do the rustc override in a useful manner?

[paulrouget]

Can you confirm that we can now do the rustc override in a useful manner?

Not yet. The override uses rustup. But afaik, servo doesn't use rustup or local cargo.

See #11361 (comment)

[shinglyu]

So what are our alternatives for the Cargo.lock issue?

• Extend cargo to "inherit" Cargo.lock in sub-directories?
• Create a script/tool in servo to setup the building environment for a project using it, copying the Cargo.lock and make sure rustup is using same rustc version?

Anything else?

[metajack]

At the All Hands, @wycats and @aturon seemed willing to add something to Cargo to help with this. I believe the core idea was to extend cargo update with a --lockfile argument.

[shinglyu]

Sound good, is there a meta bug for that? Or should we open one?

[metajack]

@shinglyu I don't think there is a bug yet. I'll file one.

[paulrouget]

Things are moving toward the right direction. We will get to a point where libservo can share its lock file and libservo can require a rustup toolchain.

Question: when a third party project wants to use the rustc version of libservo, how do we tell cargo to use libservo's rust toolchain? Would that work automatically? As in, when cargo is called, it will check the dependencies, find the libservo's .rust-toolchain file and make sure it uses that toolchain?

[paulrouget]

Dependencies so far:

• rust-lang/rustup/issues/1218
• /issues/11361
• rust-lang/cargo/issues/4353