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

$ go version 1.12.4

Does this issue reproduce with the latest release?

Yes

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

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/CC/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/CC/go/"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/CC/go/src/project/go.mod"
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build911813928=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Given the following situation:

project
├── lib1
│   └── lib1.go
├── app1
│   └── main.go
└── go.mod

• project is in the gopath under /home/CC/go/src/project/
• app1 imports lib1 with "project/lib1"
• Only the project root has a go.mod file, which contains 3rd party imports

When go build is executed in app1, lib1 is fetched locally, while 3rd party imports such as "github.com/BurntSushi/toml" are fetched remotely with the latest revision. If a "github.com/BurntSushi/toml" version is specified in the go.mod file in the project root, go build in app1 will fetch that specific version.

What did you expect to see?

go build in app1 builds without go modules, or always fetches latest revision of all dependencies. I expected the go.mod file in the project root to be ignored.

Is it intended that go module works if there is only a go mod file in the parent project directory?