Renaming dependencies in Cargo.toml

[matklad]

Implementation PR: #4953

Summary:

With cargo-features = ["rename-dependency"] in Cargo.toml, you will be able to specify dependencies as bar = { package = "foo", version = "0.1" }. That adds dependency to foo package from crates.io, which will be visible as extern crate bar.

Steps:

• cargo metadata should include information about renames, Include more information about dependencies in Cargo metadata #5583.

• outstanding bugs:

  • assertion failed: locate_ctxt.hash.is_none() when running "cargo test" rust#51259
  • rename-dependency doesn't perform hyphen/underscore translation rust#51795
  • ICE when using rename-dependency with a crate that is also a transitive dependency rust#51796
  • Renamed optional dependency should use the renamed name #5753

• Figure out to do about --features on the command line? Does --features foo/bar imply the package foo or the crate that's renamed to foo? We probably want the latter, and that's probably buggy right now.

Stabilization TODO:

• move docs from https://github.com/rust-lang/cargo/blob/5845464cf92a348f95dc6b43133c017c37fcb684/src/doc/src/reference/unstable.md#rename-dependency to proper location.
• remove feature gate

[matklad]

Note: preferably, this should be stabilized before or in tandem with rust-lang/rust#44660

[ehuss]

Some bugs have been noted recently:

• assertion failed: locate_ctxt.hash.is_none() when running "cargo test" rust#51259
• rename-dependency doesn't perform hyphen/underscore translation rust#51795
• ICE when using rename-dependency with a crate that is also a transitive dependency rust#51796

Also, there is another tracking issue for this: #5422

[matklad]

Excellent, thanks @ehuss! I've updated the original issue.

[withoutboats]

Added another bug: #5753.

[TheDan64]

rust#51796 and #5753 seem to be fixed and closed according to those threads. Can the checklist be updated?

Edit: Thanks!

[Nemo157]

New bug with optional renamed dependencies once published: #5962

[joshtriplett]

I'd definitely like to see this stabilized. One note: we need to consider the implications of stabilizing a feature like this, including to cargo dependency resolution, and to tools that parse Cargo.toml files. It would be nice to have a mechanism that specifies Cargo features the parsing tool must understand to successfully process a crate, and to incorporate that mechanism into the Cargo crate index. I'm working on a proposal for this (much simpler than past proposals).