Fix the rollback mechanism for tags during a release (magefile#392)

* this fixes the rollback mechanism for tags during a release * check for goreleaser before we do anything else

Author: natefinch

magefile.go

@@ -1,4 +1,5 @@
-//+build mage
+//go:build mage
+// +build mage
 
 // This is the build script for Mage. The install target is all you really need.
 // The release target is for generating official releases and is really only
@@ -9,6 +10,7 @@ import (
 "errors"
 "fmt"
 "os"
+"os/exec"
 "path/filepath"
 "regexp"
 "runtime"
@@ -69,6 +71,9 @@ var releaseTag = regexp.MustCompile(`^v1\.[0-9]+\.[0-9]+$`)
 
 // Generates a new release. Expects a version tag in v1.x.x format.
 func Release(tag string) (err error) {
+if _, err := exec.LookPath("goreleaser"); err != nil {
+return fmt.Errorf("can't find goreleaser: %w", err)
+}
 if !releaseTag.MatchString(tag) {
 return errors.New("TAG environment variable must be in semver v1.x.x format, but was " + tag)
 }
@@ -81,8 +86,8 @@ func Release(tag string) (err error) {
 }
 defer func() {
 if err != nil {
-sh.RunV("git", "tag", "--delete", "$TAG")
-sh.RunV("git", "push", "--delete", "origin", "$TAG")
+sh.RunV("git", "tag", "--delete", tag)
+sh.RunV("git", "push", "--delete", "origin", tag)
 }
 }()
 return sh.RunV("goreleaser")