This one is quite odd (and I'm 95% sure it's a compiler bug). We've been seeing
this a lot in the Docker %check script (where we run a subset of the upstream
unit tests). Effectively this looks something like this:

% go test $some_pkg # works
% go test $other_pkgs... $some_pkg # $some_pkg fails to build
% go test $other_pkgs... $more_pkgs... $some_pkg # works

For a recent SR[1] we hit this quite weirdly. The example is:

% go test github.com/docker/docker/daemon/cluster/executor/container
$other_pkgs
# github.com/docker/docker/vendor/github.com/Graylog2/go-gelf/gelf
home/abuild/go/src/github.com/docker/docker/vendor/github.com/Graylog2/go-gelf/gelf/reader.go:10:
can't find import: "compress/zlib"
FAIL    github.com/docker/docker/daemon/cluster/executor/container [build
failed]
% go test github.com/docker/docker/daemon/cluster/executor/container
github.com/docker/docker/daemon/logger/... $other_pkgs
ok      github.com/docker/docker/daemon/cluster/executor/container      3.026s 
coverage: 7.9% of statements

This matters because we want to drop
github.com/docker/docker/daemon/logger/..., but dropping it starts to break
unrelated tests. Ideally we should be able to create a reproducer that isn't
related to Docker.

[1]: https://build.opensuse.org/request/show/548067