go/packages: can't resolve golang_org vendored packages

[dave]

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

$ go version
go version go1.11 darwin/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
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/dave/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/dave"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
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/qx/ypfpz5jd4jqc9r2r1z_mzpwm0000gn/T/go-build540247940=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

The golang.org/x/tools/go/packages package is not able to resolve the golang_org vendored packages in src/vendor - e.g. this import. Is this expected? Is there a work-around?

package main

import (
	"go/build"
	"path/filepath"
	"testing"

	"golang.org/x/tools/go/packages"
)

func TestVendor(t *testing.T) {

	importPath := "golang_org/x/crypto/chacha20poly1305"
	fromDir := filepath.Join(build.Default.GOROOT, "src", "crypto/tls")

	cfg := &packages.Config{
		Dir:   fromDir,
		Mode:  packages.LoadTypes,
		Tests: false,
	}

	pkgs, err := packages.Load(cfg, "pattern="+importPath)
	if err != nil {
		t.Fatal(err)
	}

	if len(pkgs) != 1 {
		t.Fatalf("expected 1 package, found %d", len(pkgs))
	}

	p := pkgs[0]

	if len(p.Errors) > 0 {
		for _, err := range p.Errors {
			t.Error(err)
		}
	}

	if p.Name != "chacha20poly1305" {
		t.Fatalf("expected chacha20poly1305, found %s", p.Name)
	}
}

Output:

=== RUN   TestVendor
--- FAIL: TestVendor (0.03s)
    vendor_test.go:35: -: cannot find package "golang_org/x/crypto/chacha20poly1305" in any of:
        	/usr/local/go/src/golang_org/x/crypto/chacha20poly1305 (from $GOROOT)
        	/Users/dave/src/golang_org/x/crypto/chacha20poly1305 (from $GOPATH)
    vendor_test.go:40: expected chacha20poly1305, found 
FAIL

[heschi]

Dupe of #28375, which was duped to #26924. I just stopped looking at anything in $GOROOT/.../vendor, but I haven't thought about how good a general solution that is.