How do I get go-pkg package dependencies right?

[Krzysztof Lasocki <nzkiwi.5000%gmail.com@localhost>]

Hello,
I'm porting ArduinoBuilder to pkgsrc as wip/arduino-builder.
It depends on several Go packages, I'm making a separate pkgsrc
package for each of them not yet in the tree.
One of those is wip/go-properties-map, which in turn depends on
wip/go-paths-helper

Both packages fetch sources fine, but go-properties-map can't build
due to the compiler not being able to find the go-paths-helper source
(which fetches and builds OK when building go-properties-map)

The error is:

===> Building for go-properties-map-ad37f0cfeff29fadeabe6b2f7f852d8db1fb5c41
work/src/github.com/arduino/go-properties-map/objects.go:33:2: cannot
find package "github.com/arduino/go-paths-helper" in any of:
        /usr/pkg/go111/src/github.com/arduino/go-paths-helper (from $GOROOT)
        /usr/pkgsrc/wip/go-properties-map/work/src/github.com/arduino/go-paths-helper
(from $GOPATH)
        /usr/pkgsrc/wip/go-properties-map/work/.buildlink/gopkg/src/github.com/arduino/go-paths-helper
*** Error code 1

None of those paths exist: work/src/github.com/arduino contains only
go-properties-map/ as if blk3 from go-paths-helper (adapted from other
go packages) does not copy the right files in the right place
and work/.buildlink/ contains only include/, bin/ and lib/

So my question is: Why is this package unable to find its
dependencies? What do I need to change to get go-properties-map
building?

-- 
Ala ma bota.