x/tools/go/packages: cgo error in one package causes entire Load to fail

[dominikh]

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

$ go version
go version go1.12.3 linux/amd64
go version devel +a01d108e30 Sun Apr 14 16:19:31 2019 +0000 linux/amd64

Trying to load multiple packages with packages.Load fails if any of the packages have cgo errors:

desktop 1? ~ $ cat $GOPATH/src/sandbox/foo/*.go
package main

import (
	"fmt"
)

func main() {
	x := 42
	fmt.Printf("%w\n", x)
}
desktop ~ $ cat $GOPATH/src/sandbox/bar/*.go
package bar

import "C"

func fn() {
	C.doesnotexist()
}
desktop ~ $ cat /tmp/foo.go 
package main

import (
	"log"

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

func main() {
	cfg := &packages.Config{
		Mode: packages.LoadAllSyntax,
	}
	_, err := packages.Load(cfg, "sandbox/foo", "sandbox/bar")
	if err != nil {
		log.Fatal(err)
	}
}
desktop ~ $ go run /tmp/foo.go 
2019/04/15 01:13:57 go [list -e -json -compiled=true -test=false -export=false -deps=true -find=false -- sandbox/foo sandbox/bar]: exit status 2: # sandbox/bar
prj/src/sandbox/bar/bar.go:6:2: could not determine kind of name for C.doesnotexist
exit status 1
desktop 1? ~ $ 

I expected packages.Load to return no error, to get two packages for sandbox/foo and sandbox/bar, and sandbox/bar to have a non-empty Errors.

/cc @ianthehat @matloob

[sauyon]

After discussion with @dominikh on IRC, we've worked out the source of the bug:

cgo preprocessing always happens, and the tool doesn't expect there to be build output/failures unless the function usesExportData(cfg) evaluates to true. This causes Load function to think the driver has failed, and therefore error out before doing any analysis. Interestingly, the error code seems to only get set if -compiled=true is passed.

This bug will therefore only trigger if packages.NeedExportsFile is not set and either packages.NeedTypes is not set or packages.NeedTypesInfo is set.

Relevant code:
usesExportData: https://github.com/golang/tools/blob/212fb13d595e5faf79425c78ae101012873a81a1/go/packages/packages.go#L1073
Relevant exception: https://github.com/golang/tools/blob/212fb13d595e5faf79425c78ae101012873a81a1/go/packages/golist.go#L818

EDIT: Easy workaround for now it set packages.NeedExportsFile

[gopherbot]

Change https://golang.org/cl/185077 mentions this issue: Ignore more errors in go list

[matloob]

This is fixed by golang.org/cl/192330.

[matloob]

This is fixed by golang.org/cl/192330