Allow specifying alternate sources for dependencies

[codyps]

When using a package manager that uses source code as the "package", we need to grab source at a different step than build.

Also, at times it's necessary to patch dependencies, which being able to point to a raw directory would allow.

I imagine we'd provide some mapping between "url#hash" and "directory".

One possibility would be to allow Cargo.lock to be edited to point to new locations/urls/hashes which don't match Cargo.toml without automatically re-updating it (and blowing away those changes).

[steveklabnik]

This is already possible with a local override in .cargo/config

[codyps]

Interesting. Are local overrides documented somewhere? http://doc.crates.io/config.html doesn't seem to mention them.

[steveklabnik]

On that page,

# An array of paths to local repositories which are to be used as overrides for
# dependencies. For more information see the Cargo Guide.
paths = [ "/path/to/override" ]

http://doc.crates.io/guide.html#overriding-dependencies

is said section 😄

[codyps]

Ah, thanks. I was expecting something more complicated (I didn't see any hashes mentioned, so my eyes just skipped past them).

I'm a bit surprised the behavior here (override every dependency with the same name even if it refers to a different url/rev) is different from the behavior when a project with a dep on one version of a library (A) also depends on anther lib (B) that pulls another version of the library A (both versions are included in the build).

Is this intentional?

[alexcrichton]

Yes, as @steveklabnik mentioned the method for doing this is overriding dependencies, and it's currently done via overriding package names. @jmesmon could you open a new bug about overrides perhaps being a bit too broad and maybe adding a system to hone precisely what's overridden?

[alexcrichton]

Thanks @jmesmon!

[fxdave]

@alexcrichton Is there a way of doing this, but for git dependencies?

I've got a workspace that contains member crates. And several member crates have a dependency using a git url, however that dependency crate is also in my workspace, so I want to overwrite it with my local path without touching the member's Cargo.toml. And I don't want to override it inside the member, because that is valid if somebody clones that member alone.

member/Cargo.toml <- this has the dependency as git url
common-lib/* <- this is the local version of that dependency
Cargo.toml <- I want to override it here to my local path

[weihanglo]

Hello @fxdave, this issue is quite old and the approach here might not be what you want. Without any further detail, it sounds [patch] can help you get through it. I'd suggest taking a look. It works with both Cargo.toml and .cargo/config.toml