Copy from GOPATH interacts poorly with flatten!

[ax-nathan]

Took me quite some time to figure out why "flatten by default" wasn't (apparently) working!

Scenario

• Packages A & B both exist in GOPATH.
• Packages A & B both use glide.
• Packages A & B both vendor package C in glide.yaml.
• Package A vendors package B.
• Package B DOES NOT have vendor/ in VCS.
• Package B DOES have vendor/ on disk in GOPATH.

Result

• glide up in Package A (with flatten enabled) copies Package B from GOPATH.
• The copy of Package B includes the vendor/ directory from disk.
• The resulting build includes A/vendor/C and A/vendor/B/vendor/C.
• Bad Things(tm)

Proposal

• --skip-gopath should default to true, or
• "flatten by default" becomes aware of vendor/ directories copied from GOPATH, and prevents the copying of packages which should be flattened.

[mattfarina]

I've been having issues with the gopath copying myself. we need to do something about that.

I'm considering:

• opt-in to gopath copying.
• making sure the gopath version isn't dirty. But, this won't find anything being ignored.
• trying to introspect what's ignored or not along with dirtyness to figure out what to copy or skip. This would be complex.

Caching and reuse are hard.

[ax-nathan]

I'd vote for "opt-in to go path copying" as a quick, safe fix. Seems like the current method is an overly aggressive performance optimization, but results in "surprising" behavior for the development use case. At a minimum, perhaps the README needs a "Gotchas" section where things like this are called out?

[mattfarina]

8615f59 made the copying from the GOPATH opt-in. This will be in the next release.