Temporarily replacing a module

log.txt

~ % mkdir /tmp/apt
~ % cd /tmp/apt
/tmp/apt % cat > apt.go <<'EOT'
package main

import (
	"bytes"
	"log"

	"github.com/stapelberg/godebiancontrol"
)

const ctrlfile = `
Package: quake
`

func main() {
	paragraph, err := godebiancontrol.Parse(bytes.NewReader([]byte(ctrlfile)))
	if err != nil {
		log.Fatalf("apt: %v", err)
	}
	log.Printf("paragraph: %+v", paragraph)
}
EOT

/tmp/apt % go build
go: finding github.com/stapelberg/godebiancontrol v0.0.0-20180408134423-8c93e189186a
go: downloading github.com/stapelberg/godebiancontrol v0.0.0-20180408134423-8c93e189186a
go: extracting github.com/stapelberg/godebiancontrol v0.0.0-20180408134423-8c93e189186a

# Let’s do a change which we want to evaluate. In this case, a re-implementation of godebiancontrol:

/tmp/apt % mkdir /tmp/debctrl
/tmp/apt % cd /tmp/debctrl
/tmp/debctrl % go mod init github.com/stapelberg/godebiancontrol
/tmp/debctrl % cat > ctrl.go <<'EOT'
package godebiancontrol

import (
	"fmt"
	"io"
)

type Paragraph map[string]string

func Parse(input io.Reader) (paragraphs []Paragraph, err error) {
	return nil, fmt.Errorf("my custom change is broken!")
}
EOT

# Let’s evaluate this change:
/tmp/debctrl % cd /tmp/apt
/tmp/apt % go mod edit -replace=github.com/stapelberg/godebiancontrol=/tmp/debctrl
/tmp/apt % go build && ./apt
2018/12/24 13:24:56 apt: my custom change is broken!
/tmp/apt % go mod edit -dropreplace=github.com/stapelberg/godebiancontrol

# Just to verify that our build is not broken by the temporary module replacement:

/tmp/apt % go build
/tmp/apt % ./apt
2018/12/24 13:25:46 paragraph: [map[Package:quake]]