Need a way to handle subpackages

[proppy]

Some non-trivial application (like etcd) import subpackages from their own import paths, and thus expect to be stored at a fixed location in GOPATH, example:

import "github.com/coreos/etcd/log"

Currently he onbuild variant ADD the source code in GOPATH/src/app, this causes go get ./... to fetch this kind of dependencies remotely and possibly ignore local change.

One possible solution is to add support for a .godir file defining the application import path at the root of the source directory, see:
GoogleCloudPlatform/golang-docker#10
GoogleCloudPlatform/golang-docker#12

[yosifkit]

That sounds good to me.

/cc @tianon

[tianon]

Do you think we could do it via ENV in the onbuild-ing Dockerfile instead
to minimize our impact on the upstream repo? This would also have the
interesting side effect of being easily overwritten at container run time
if it was necessary to do so for some esoteric reason. Thoughts?

[proppy]

@tianon good idea, I originally went for .godir because someone raised it was already used by app w/ heroku golang build packs

[tianon]

Hmm, parity with Heroku is a solid justification. Also, during the ONBUILD
stuff we wouldn't have access to ENV var directly, so we'd have to process
the Dockerfile to extract it (which is really easy to do, but not nearly as
easy as just taking the contents of ".godir" verbatim).