cmd/go: vendor directory in src/cmd breaks build in module mode

[rsc]

GOROOT/src/cmd's use of a nested vendor directory makes it not work with module mode.
We'll have to fix that at some point.

[myitcv]

Does this also apply to the top-level src/vendor directory?

export GOPATH=$(mktemp -d)
cd $(mktemp -d)
mkdir hello
cd hello
go mod init example.com/hello
go test vendor/golang_org/x/net/http/httpproxy

results in:

# vendor/golang_org/x/net/http/httpproxy_test [vendor/golang_org/x/net/http/httpproxy.test]
/home/myitcv/gos/src/vendor/golang_org/x/net/http/httpproxy/proxy_test.go:304:6: undefined: httpproxy.ExportUseProxy
/home/myitcv/gos/src/vendor/golang_org/x/net/http/httpproxy/proxy_test.go:314:8: undefined: httpproxy.ExportUseProxy
/home/myitcv/gos/src/vendor/golang_org/x/net/http/httpproxy/proxy_test.go:325:6: undefined: httpproxy.ExportUseProxy
FAIL    vendor/golang_org/x/net/http/httpproxy [build failed]

Or would you prefer this as a separate issue?

[rsc]

It's basically the same. It can be this issue too.

[bcmills]

Hmm, this might be the same underlying cause as the failure @cespare observed in #26996 (comment).