The root cause is someone added "import context" code to golang/mock which broke it against older go releases (older than 1.7).
I have a fix for it bundled into THRIFT-4351 where I call "go get" twice with a sed in between to force it to import golang.org/x/net/context instead. https://github.com/golang/mock/pull/118 The ubuntu-xenial official build docker image we use has go 1.6.2 in it because that's what Ubuntu comes with. This was the only build failure; once the next CI build passes I will be merging this one in, which clears up a bunch of issues and adds a bit more documentation for language support and what features each language provides (but not a report of what features are cross-tested.. that is something we want to generate programmatically). - Jim
