Specify minimum glide version in glide.yaml

[HelloGrayson]

Possible to enforce a minimum version of glide in glide.yaml?

Running into an issue where 0.11 doesn't support vanity import paths, but 0.12 does.

This results in very confusing errors which correlate to the bug in 0.11:

[INFO]  Downloading dependencies. Please wait...
[INFO]  Setting references for remaining imports
[ERROR] Failed to set version on go.uber.org/yarpc/internal/sync to : https://go.uber.org/yarpc/internal/sync Not Found
[ERROR] Failed to set version on go.uber.org/yarpc/internal/errors to : https://go.uber.org/yarpc/internal/errors Not Found
[ERROR] Failed to set version on go.uber.org/yarpc/internal/filter to : https://go.uber.org/yarpc/internal/filter Not Found
[ERROR] Failed to set version on go.uber.org/yarpc/internal/interceptor to : https://go.uber.org/yarpc/internal/interceptor Not Found
[ERROR] Failed to set version on go.uber.org/yarpc/internal/request to : https://go.uber.org/yarpc/internal/request Not Found
[ERROR] Failed to set version on go.uber.org/yarpc/internal/baggage to : https://go.uber.org/yarpc/internal/baggage Not Found
[ERROR] Failed to set version on go.uber.org/yarpc/transport to : https://go.uber.org/yarpc/transport Not Found
[ERROR] Failed to set version on go.uber.org/yarpc/internal to : https://go.uber.org/yarpc/internal Not Found
[INFO]  Project relies on 11 dependencies.
An Error has occurred

Since my project already knows about the bug, and therefor cant support Glide 0.11, I would much rather users get something like:

[ERROR] Must use Glide >= 0.12

Suggesting adding something like so to glide.yaml:

glide_version: >= 0.12

The the Glide binary can compare that against itself, and blow up if the constraint doesn't match.

[mattfarina]

I'd like to get this in for Glide and Go itself. Once GPS is pulled in completely we'll look into this.

[HelloGrayson]

Sounds great.

I'd like to read more about GPS - where could I do that?

[sdboyer]

@breerly i've tried to make the README a reasonable starting point