By default, Go pulls imported dependencies by grabbing the latest version in master (github) or default (mercurial) if it cannot find the dependency on your GOPATH. And while this workflow is quite simple to grasp, it has become somewhat difficult to tightly control. Because all software change incurs some risk, I'd like to reduce the risk of this potential change in a manageable and repeatable way and avoid inadvertently picking up changes of a dependency, especially when running clean builds via CI server or preparing to deploy.
What is the most effective way I can pin (i.e. lock down or capture) a package dependency so I don't find myself unable to reproduce an old package, or even worse, unexpectedly broken when I'm about to release?
---- Update ----
Additional info on the Current State of Go Packaging. While I ended up (as of 7.20.13) capturing dependencies in a 3rd party folder and managing updates (ala Camlistore), I'm still looking for a better way...
Here is a great list of options.
Also, be sure to see the go 1.5 vendor/ experiment to learn about how go might deal with the problem in future versions.
You might find the way Camlistore does it interesting.
See the third party directory and in particular the update.pl and rewrite-imports.sh script. These scripts update the external repositories, change imports if necessary and make sure that a static version of external repositories is checked in with the rest of the camlistore code.
This means that camlistore has a completely repeatable build as it is self contained, but the third party components can be updated under the control of the camlistore developers.
There is no built in tooling for this in go. However you can fork the dependencies yourself either on local disk or in a cloud service and only merge in upstream changes once you've vetted them.
The 3rd party repositories are completely under your control. 'go get' clones tip, you're right, but you're free to checkout any revision of the cloned-by-go-get or cloned-by-you repository. As long as you don't do 'go get -u', nothing touches your 3rd party repositories already sitting at your hard disk.
Effectively, your external, locally cloned, dependencies are always locked down by default.
There is a project to help you in managing your dependencies. Check gopack
godep
I started using godep early last year (2014) and have been very happy with it (it met the concerns I mentioned in my original question). I am no longer using custom scripts to manage the vendoring of dependencies as godep just takes care of it. It has been excellent for ensuring that no drift is introduced regardless of timing or a machine's package state. It works with the existing mechanism of go get and introduces the ability to pin (godep save) and restore (godep restore) based on Godeps/godeps.json.
Check it out: