`vndr init` produces wrong `vendor.conf` for versioned packages

[AkihiroSuda]

$ cat foo.go
package foo

import (
        "github.com/containerd/cgroups/v2"
)

func Foo(a, b string) (*v2.Manager, error) {
        return v2.LoadManager(a, b)
}
$ vndr init

Result:

github.com/containerd/cgroups/v2 3f83850c48d225466698517ad34f4848d2ddaeeb
github.com/containerd/cgroups/stats/v1 3f83850c48d225466698517ad34f4848d2ddaeeb
github.com/coreos/go-systemd d657f9650837651364841f00795b417b1ca43c1f
github.com/docker/go-units 519db1ee28dcc9fd2474ae59fca29a810482bfb1
github.com/godbus/dbus/v5 43c7e6d0673024b2dcdf97cb4d766efec9da7e9b
github.com/opencontainers/runtime-spec e09c7c488e298f2147734e657eba72fc9fa10ca9
github.com/pkg/errors 49f8f617296114c890ae0b7ac18c5953d2b1ca0f
golang.org/x/sys 548cf772de5052aa878ccb47cdeb7d262b75c8ec
github.com/coreos/go-systemd d657f9650837651364841f00795b417b1ca43c1f

Expected result:

github.com/containerd/cgroups 3f83850c48d225466698517ad34f4848d2ddaeeb
github.com/coreos/go-systemd/v22 d657f9650837651364841f00795b417b1ca43c1f
...

Note:

• github.com/containerd/cgroups in vendor.conf MUST NOT contain /v2 suffix because v2 is a git subdirectory, not a version string in go.mod
• github.com/coreos/go-systemd/v22 MUST contain /v22 suffix because v22 is a version string in go.mod, not a git subdirectory

I'm not sure how we can support this without parsing go.mod.

vndr version 0.1.0

[thaJeztah]

~Looks like the package for parsing gomod is "internal" 😞 https://golang.org/pkg/cmd/go/internal/modfile/~

~Looking at other projects, there are valid use-cases to use that package though, for example; I found this project to run a go proxy, which looks to copy those files in order to use them; https://github.com/sirkon/goproxy/blob/bac7c5e34d4e2ec415275c4f2ddc5c1c86e74fd6/internal/modfile/read.go. Haven't looked yet, but perhaps we should propose that package to not be marked "internal"~

nevermind: looks like it moved to golang.org/x/mod: https://github.com/golang/mod/blob/c90efee705eefc6efa975842f5e85f455b0b4639/modfile/read.go

[LK4D4]

@AkihiroSuda that's a bummer. I wonder if it's easy to detect and produce warnings. Thanks for taking a look.