golang: custom import paths

[yosifkit]

Add docs for the magic godir (mention go-wrapper?)

Added here: docker-library/golang#10

[yosifkit]

ping @Moghedrin

[tianon]

Just for reference, here's the current usage text:

$ docker run -it --rm golang go-wrapper

usage: go-wrapper command [args]

This script assumes that is is run from the root of your Go package (for
example, "/go/src/app" if your GOPATH is set to "/go").

The main feature of this wrapper over the native "go" tool is that it supports
the addition of a ".godir" file in your package directory which is a plain text
file that is the import path your application expects (ie, it would be something
like "github.com/jsmith/my-cool-app").  If this file is found, the current
package is then symlinked to /go/src/<.gopath> and the commands then use that
full import path to act on it.  This allows for applications to be universally
cloned into a path like "/go/src/app" and then automatically built properly so
that inter-package imports use the existing source instead of downloading it a
second time.  This also makes the final binary have the correct name (ie,
instead of being "/go/bin/app", it can be "/go/bin/my-cool-app"), which is why
the "run" command exists here.

Available Commands:

  go-wrapper download
  go-wrapper download -u
    (equivalent to "go get -d [args] [godir]")

  go-wrapper install
  go-wrapper install -race
    (equivalent to "go install [args] [godir]")

  go-wrapper run
  go-wrapper run -app -specific -arguments
    (assumes "GOPATH/bin" is in "PATH")

[tianon]

.godir is a great hack, but Go 1.4 added Custom Import Paths that we now prefer instead: https://golang.org/s/go14customimport

[yosifkit]

We don't support golang versions older than 1.4 now, so we can remove the "undocumented .godir". 😈