cmd/go: emit an explicit error when packages in GOPATH/src/vendor overlap with GOROOT/src/vendor

[javasgl]

What version of Go are you using (go version)?

$ go version
go version go1.13 darwin/amd64

Does this issue reproduce with the latest release?

only in go1.13 happened, back to go1.12.9 can fix this

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/username/Library/Caches/go-build"
GOENV="/Users/username/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH=""
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/b1/bhf9j3q96m75223l3hh41ccw0000gn/T/go-build173249759=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

go install -v ./...

What did you expect to see?

no errrors

What did you see instead?

src/vendor/golang.org/x/net/http2/frame.go:17:2: use of vendored package not allowed
src/vendor/google.golang.org/grpc/internal/transport/controlbuf.go:28:2: use of vendored package not allowed
src/vendor/golang.org/x/net/http2/transport.go:35:2: use of vendored package not allowed

[mvdan]

Please provide full instructions to show that this worked on 1.12, and broke in 1.13. For example, using the official Docker images.

[bcmills]

@javasgl, to amplify what @mvdan said: go install -v ./... doesn't help us reproduce your problem unless you also include the contents of the module or repo that you were working in.

In particular, do the import statements in your code include the vendor/ prefix?

This change probably relates to CL 164619, but we did add a regression test in that CL to try to avoid any change in behavior for existing code using the correct import paths.

[psanford]

I think I ran into the same issue. I made an example repo here to demonstrate the issue: https://github.com/psanford/gobug34068

If you checkout that repo and set your GOPATH to the git working directory you can try building package example.com/foo from go 1.12 (works) vs 1.13 (errors). example.com/foo is a grpc client hello world example.

Grpc and its dependencies were vendored in src/vendor via gvt.

[javasgl]

@bcmills same project structure with @psanford