proposal: Update go.mod to indicate mod=mod and ignore vendor dir

[DavidGamba]

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

$ go version
go version go1.14.3 linux/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/david/.cache/go-build"
GOENV="/home/david/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY="github.com/DavidGamba"
GONOSUMDB="github.com/DavidGamba"
GOOS="linux"
GOPATH="/home/david/go"
GOPRIVATE="github.com/DavidGamba"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/david/opt/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/david/opt/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/david/my-repo/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-build183891728=/tmp/go-build -gno-record-gcc-switches"

What did you do?

1. Create a new monorepo dir:

mkdir mod-mod && cd mod-mod
go mod init github.com/DavidGamba/mod-mod

2. Create a vendor directory that is a third party vendor dir, not Go code vendor.

mkdir vendor && touch vendor/hello

3. Create a main.go file with an external import, and try build it:

$ go build
main.go:9:2: cannot find package "." in:
        /home/david/test/mod-mod/vendor/github.com/DavidGamba/go-getoptions

$ go build -mod=mod
go: finding module for package github.com/DavidGamba/go-getoptions
go: found github.com/DavidGamba/go-getoptions in github.com/DavidGamba/go-getoptions v0.19.0

Common workarounds don't work.

$ cd vendor
$ go mod init github.com/DavidGamba/mod-mod/vendor
go: creating new go.mod: module github.com/DavidGamba/mod-mod/vendor
$ cd ..
$ go build
go: inconsistent vendoring in /home/david/test/mod-mod:
        github.com/DavidGamba/go-getoptions@v0.19.0: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt

run 'go mod vendor' to sync, or use -mod=mod or -mod=readonly to ignore the vendor directory

What did you expect to see?

An option to tell go to always run in mod mode so it ignores the vendor directory used by other code in the monorepo. The option should be persisted in the go.mod file so there is no need to pass it to the command line every time and so other tools like gopls know about it.

What did you see instead?

vendor mode is assumed wrongly due to the presence of a vendor/ directory.

[seankhliao]

have you considered setting GOFLAGS="-mod=mod"?

[DavidGamba]

The problem with GOFLAGS is that only applies for my environment and each executable in our project can be built with plain go build unless we do a release build were we insert the metadata with -ldflags in our build system.

It is a workaround every developer will be forced to apply which I suppose it is OK but it would be better if the go.mod file had that information.