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Go += Package Versioning

Last updated 2 years ago by Russ Cox


We need to add package versioning to Go.

More precisely, we need to add the concept of package versions to the working vocabulary of both Go developers and our tools, so that they can all be precise when talking to each other about exactly which program should be built, run, or analyzed. The go command needs to be able to tell developers exactly which versions of which packages are in a particular build, and vice versa.

Versioning will let us enable reproducible builds, so that if I tell you to try the latest version of my program, I know you're going to get not just the latest version of my code but the exact same versions of all the packages my code depends on, so that you and I will build completely equivalent binaries.

Versioning will also let us ensure that a program builds exactly the same way tomorrow as it does today. Even when there are newer versions of my dependencies, the go command shouldn't start using them until asked.

Although we must add versioning, we also must not remove the best parts of the current go command: its simplicity, speed, and understandability. Today, many programmers mostly don't pay attention to versioning, and everything mostly works fine. If we get the model and the defaults right, we should be able to add versioning in such a way that programmers still mostly don't pay attention to versioning, and everything just works better and is easier to understand. Existing workflows should change as little as possible. Releasing new versions should be very easy. In general, version management work must fade to the background, not be a day-to-day concern.

In short, we need to add package versioning, but we need to do it without breaking go get. This post sketches a proposal for doing exactly that, along with a prototype demonstration that you can try today and that hopefully will be the basis for eventual go command integration. I intend this post to be the start of a productive discussion about what works and what doesn't. Based on that discussion, I will make adjustments to both the proposal and the prototype, and then I will submit an official Go proposal, for integration into Go 1.11 as an opt-in feature.

This proposal keeps the best parts of go get, adds reproducible builds, adopts semantic versioning, eliminates vendoring, deprecates GOPATH in favor of a project-based workflow, and provides for a smooth migration from dep and its predecessors. That said, this proposal is still also in its early stages. If details are not right yet, we will take the time to fix them before the work lands in the main Go distribution.

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