x/tools/cmd/goimports: does not find import with package in vendor/, GOFLAGS="-mod=vendor" and empty $GOPATH/pkg directory

[fho]

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

$ go version
go version go1.12.4

goimports from from https://github.com/golang/tools, commit d1a3278ee74994e9aa609e9e711c616bba677d5d

Does this issue reproduce with the latest release?

Yes, reproducible with go 1.12.5

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/fho/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/fho/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/tmp/testproject/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-build188015067=/tmp/go-build -gno-record-gcc-switches"

What did you do?

1. Create a new golang project using go.mod.
   The project has a a main.go file that imports the external dependency github.com/lib/pq.
   The external modules are downloaded into vendor/ via go mod vendor.

mkdir -p /tmp/testproject
cd /tmp/testproject
go mod init "testproject"
echo 'package main

import (
	"fmt"
	"github.com/lib/pq"
)

func main() {
	var test pq.StringArray

	fmt.Println(test)
}' > main.go
go mod vendor

2. Remove the "github.com/lib/pq" import from main.go:

sed -i '/"github.com\/lib\/pq"/D' main.go

3. Remove $GOPATH/pkg, run goimports with GOFLAGS=-mod=vendor:

sudo rm -rf $(go env GOPATH)/pkg
GOFLAGS="-mod=vendor" goimports -d main.go

What did you expect to see?

goimports detects the missing github.com/lib/pq import and shows it in the diff.

What did you see instead?

goimports does not find the missing github.com/lib/pg import and prints no diff.

[heschi]

Thanks for the excellent repro. The immediate problem is that there's no structured way for goimports to tell if vendoring is enabled. From https://github.com/golang/tools/blob/d1a3278ee74994e9aa609e9e711c616bba677d5d/imports/mod.go#L241-L248:

		if strings.HasPrefix(importPath, "vendor/") {
			// Ignore vendor dirs. If -mod=vendor is on, then things
			// should mostly just work, but when it's not vendor/
			// is a mess. There's no easy way to tell if it's on.
			// We can still find things in the mod cache and
			// map them into /vendor when -mod=vendor is on.
			return
		}

Possibly we should just attempt to parse $GOFLAGS. I think everything will work after that.

[heschi]

I fixed this in https://golang.org/cl/203017.

[fho]

thanks a lot @heschik

[alexshkatov]

The issue still persists on go1.13.1 (exactly the same scenario) . It seems like the latest goimports tool ignores GOFLAGS completely.

[heschi]

You're right. Sorry about that; the unit test coverage was good but I missed that GOFLAGS wasn't hooked up in the actual binary.