Allow pinning of templates to version via SHA/branch or tag (release)

[alexellis]

Expected Behaviour

I should be able to pin a template to a specific version via SHA/branch or tag (release) so that I can control my build pipeline and keep it reproducible.

Current Behaviour

I can clone and checkout a templates repo manually, but not via faas-cli template pull.

Possible Solution

faas-cli template pull https://cdn.com/repo.git#0.1.0

faas-cli template pull https://cdn.com/repo.git#dev

faas-cli template pull https://cdn.com/repo.git#d22af7cf74b7e24b37f46f8c60cb912751e93eab

If no # is given then the behaviour should default to the current functionality.

[alexellis]

cc @LucasRoesler who wrote the original code

[LucasRoesler]

dep uses this format with an @ instead of # dep ensure -add github.com/pkg/foo@^1.0.1

NPM also uses the same format. Should we also use that?

[alexellis]

That works for me 👍

[alexellis]

Not sure if we should try to support the full semantics though like ^0.1.0 etc

[LucasRoesler]

I agree, we should start with only pinning specific names or shas

[alexellis]

Sounds good to me

[LucasRoesler]

@alexellis i ran into a small issue with using @ for the pinning. It is really hard to determine how to parse an ssh based url, e.g. ssh://user@host.xz/path/to/repo.git/ and ssh://user@host.xz/path/to/repo.git@feature/branch. I have the tests all setup and that is the one that keeps failing. This is mostly an issue because if we support branch names, then we can't easily distinguish between a branch or a host with path.

We could exclude ssh urls that do not include the username, ie require ssh://user@host.xz/path/to/repo.git or we could switch back to the # format, since # character isn't used throughout the rest of the url and is not even allowed in github urls (at least all of my attempts to clone a known repo with a url fragment added failed).

Or, perhaps someone might have a suggestion about how to distinguish ssh://user@host.xz/path/to/repo from ssh://host.xz/path/to/repo@feature/branch, so that the first is recognized as a repo url without a pin and the second as a pinned url.