x/tools/go/packages: NeedImports doesn't populate Imports field when NeedDeps not set

[dmitshur]

Environment

$ go version
go version go1.12.4 darwin/amd64

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/dmitshur/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/dmitshur/go"
GOPROXY="https://proxy.golang.org"
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/var/folders/3m/rg2zm24d1jg40wb48wr0hdjw00jwcj/T/tmp.JaaD6nLe/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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/3m/rg2zm24d1jg40wb48wr0hdjw00jwcj/T/go-build560539665=/tmp/go-build -gno-record-gcc-switches -fno-common"

Issue

packages.NeedImports is documented as:

// NeedImports adds Imports. If NeedDeps is not set, the Imports field will contain
// "placeholder" Packages with only the ID set.
NeedImports

I ran the following command at the root of a module, inside that directory:

package main

import (
	"fmt"
	"log"

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

func main() {
	cfg := &packages.Config{
		//Mode: packages.NeedImports | packages.NeedDeps, // works
		Mode: packages.NeedImports, // doesn't work
	}
	pkgs, err := packages.Load(cfg, ".")
	if err != nil {
		log.Fatalln("packages.Load:", err)
	}
	if len(pkgs) != 1 {
		log.Fatalln("got something other than 1 package")
	}
	p := pkgs[0]
	if len(p.Errors) > 0 {
		log.Fatalln("p.Errors:", p.Errors)
	}
	fmt.Println("Imports:")
	for _, i := range p.Imports {
		fmt.Printf("  • %s\n", i.ID)
	}
	if len(p.Imports) == 0 {
		fmt.Println("  (none)")
	}
}

With this go.mod file:

module m

go 1.12

require golang.org/x/tools v0.0.0-20190429184909-35c670923e21

With packages.Config.Mode set to just packages.NeedImports, the Imports field is not populated at all:

Imports:
  (none)

With it set to packages.NeedImports | packages.NeedDeps, it works as expected:

Imports:
  • golang.org/x/tools/go/packages
  • log
  • fmt

/cc @ianthehat @matloob

[gopherbot]

Change https://golang.org/cl/186337 mentions this issue: go/packages: allow types loading without NeedDeps