Add subcommand to download the crate source

[gsingh93]

It would be nice to be able to download the source for a crates.io crate. Currently, I either google the repository name to find the github page, or find the crate on crates.io and find the repository link on the crate page. Not only is this process long, but it also may not always work as some crates may have generic and hard to search names, may be hosted on less popular hosting platforms, or may not have include the repository link in the manifest.

A subcommand would be useful to quickly download the source without running into these issues.

[withoutboats]

cc me

[JanLikar]

How do you think this subcommand should be named? Should it essentially work like git clone?

[gsingh93]

Maybe cargo source or cargo get-source? I prefer the former but don't feel too strongly about the name.

[alexcrichton]

@JanLikar yeah I've thought in the past that cargo clone may be a good name for something like this, it could even check out the git repo if it's available or just download the source from crates.io (depending on what's selected)

[JanLikar]

I'm willing to do this, but I would need some guidance. @alexcrichton, would you be my mentor?

[alexcrichton]

Certainly! You'll likely want to start this outside of this repo and use the cargo crate on crates.io Once you've got that you'll do something along the lines of:

• Construct a Source. This is done through various concrete implementations which are found in src/cargo/sources
• Update the source
• Download the package
• Call get to get the Package from which you can get the source.

You may want to also explore other cargo subcommands to explore how to set up the CLI.

[JanLikar]

Why shouldn't I just work with a copy of the master branch?

[retep998]

@JanLikar Because it is fairly trivial to cargo install an external version so that as soon as you get it written and working, people can immediately use it without having to wait for it to get merged into cargo and proliferate into the version of Rust they use. Also it acts as a sort of stabilization period.

[alexcrichton]

@JanLikar yeah what @retep998 says is right, and we also unfortunately can't have "unstable cargo subcommands" so anything added would be instantly stable, and we may not be ready to commit to this.

[lifthrasiir]

FYI @JanLikar has since created the cargo-clone for this exact purpose. (I note that here because I was asked about the feature and found that the subcommand is not yet mentioned in this issue.)

[joshtriplett]

cargo-clone is useful; however, it would also be nice to have a cargo-download that downloads the .crate file, with checksum verification (and optional specification of a version other than the latest).