workflow to separate dependency install step from the build step

[gregwebs]

I think cargo has great defaults, but it isn't meeting the needs for all my workflows.

On a continous integration server, to setup my cache I want to run cargo build --only-dependencies, which does not attempt to compile my program and instead just installs the Cargo.lock dependencies.

This workflow is supported by Haskell's stack tool (which Cargo learn other things from also, including docker integration and snapshots).

I apologize if there is already a way to achieve this functionality: I am not an experienced Cargo user.

[KalitaAlexey]

@gregwebs,
What do you mean under install the Cargo.lock dependencies?
Do you want them to be downloaded and that's all?

[gregwebs]

That would be a different workflow, perhaps --download-only. I want to build all the library dependencies also.

[KalitaAlexey]

Look at #3567

[gregwebs]

oh, perfect! That didn't turn up in my initial search

[gregwebs]

Actually, I will keep this open since the PR is still open (maintainers may change according to their worfklows).

[gregwebs]

Ahh, I see there is already an issue too. Sorry, I probably should have been able to find these in my searching.
#2644