[greysteil]

Cargo performs dependency resolution, so fetching from git would (and does) significantly slow it down - it wound need to perform git operations to get the tags for each dependency (quick) and then checkout each tag to look for the subdependencies of that package at that version (slow).

Having a central registry is a must for package managers that perform version resolution and want to do so quickly, as it can serve them all the metadata they need to do that resolution.

[steveklabnik]

My perception is that the initial clone is slow, but that’s it. A detailed comparison with actual numbers would be interesting!

When you depend on a git dep, you can say if you want a particular branch, tag, rev, whatever. So it’s only a clone + checkout. From there you read the Cargo.toml, same as anything else. That’s my understanding anyway, it’s been a while since I poked at the guts.

[greysteil]

You’re totally right - I was thinking of Composer, which does flat resolution for git sources so has to go through the above. Cargo sidesteps that issue completely by taking the head commit or whatever’s asked for :-)