Here's an example of a simple Google Appengine app written in Go that has vendored dependencies.
To replicate it, clone down the repository and try to deploy it to appengine using the gcloud
tool. You'll need to make sure you've installed the app-engine-go
$ gcloud app deploy
[...output redacted...]
ERROR: (gcloud.app.deploy) Error Response: [9] Deployment contains files that cannot be compiled: Compile failed:
2017/05/11 19:07:24 go-app-builder: Failed parsing input: parser: bad import "unsafe" in vendor/golang.org/x/net/ipv6/bpfopt_linux.go
Here's information about Gcloud version:
$ gcloud version
Google Cloud SDK 154.0.1
app-engine-go
app-engine-python 1.9.52
bq 2.0.24
core 2017.05.04
gcloud
gsutil 4.25