为什么纵梁找不到包?

Any idea how can I fix the error below? I have a go generator (stringer) which I try to run but it keeps reporting that it can't find a package import although the package is definitely imported.

stringer: checking package: main.go:13:3: could not import example.io/api/util (can't find import: example.io/api/util)
main.go:33: running "stringer": exit status 1

From this thread:

Seems to be a silly thing: 4 part import are usually subpackages and these must be "installed" before you can use them. I ran the following on the command line to resolve my problem:

So try first:

go install <yourpackage>

Ad see if go generate works after that.

Make sure to use the latest go 1.4.2 and to update your stringer as well:

go get -u golang.org/x/tools/cmd/stringer