Teach rustpkg about branches and tags, not just repositories

[catamorphism]

Sub-bug of #5677

For remote packages, rustpkg could infer versions from branches and tags; however, right now it only knows about the URL for a particular git repository.

[emberian]

Triage bump

[catamorphism]

I talked with @graydon about this, and we won't support branches. #8032 implements the remaining support for tags. Once #8032 lands, this issue can be closed.

[emberian]

@catamorphism is it because branches are moving targets, which a package should never target?

[graydon]

It's more that I suspect rustpkg should treat tags and branches as opaque version strings (likewise exact revision numbers and hashes) that it passes through without trying to reason about unless they parse as semvers. It's drifting into "growing a meta vcs" to try to look inside them. So I think you can probably -specify- a branch, but it'll be a very unwise move since as you say, it's a moving target at checkout time.

[emberian]

The PR as it is now will only handle tags, not any ref, so you can't
actually specify branches (not that I think this is a bad thing, due to
moving target)

On Wed, Jul 24, 2013 at 11:09 PM, Graydon Hoare [email protected]:

It's more that I suspect rustpkg should treat tags and branches as opaque
version strings (likewise exact revision numbers and hashes) that it passes
through without trying to reason about unless they parse as semvers. It's
drifting into "growing a meta vcs" to try to look inside them. So I think
you can probably -specify- a branch, but it'll be a very unwise move since
as you say, it's a moving target at checkout time.

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[graydon]

Oh. Yeah, it should probably not force the tag interpretation as that won't work for other opaque refspecs (eg. revids)

[catamorphism]

#8032 landed, so this is done.