make shell-local post-processor return copy of previous artifact

builder/docker/artifact_import.go

@@ -34,12 +34,10 @@ func (a *ImportArtifact) String() string {
 	if tags == nil {
 		return fmt.Sprintf("Imported Docker image: %s", a.Id())
 	}
-	cast := tags.([]interface{})
+	cast := tags.([]string)
 	names := []string{}
 	for _, name := range cast {
-		if n, ok := name.(string); ok {
-			names = append(names, n)
-		}
+		names = append(names, name)
 	}
 	return fmt.Sprintf("Imported Docker image: %s with tags %s",
 		a.Id(), strings.Join(names, " "))

post-processor/docker-push/post-processor.go

@@ -106,11 +106,9 @@ func (p *PostProcessor) PostProcess(ctx context.Context, ui packer.Ui, artifact
 	names := []string{artifact.Id()}
 	tags := artifact.State("docker_tags")
 	if tags != nil {
-		cast := tags.([]interface{})
+		cast := tags.([]string)
 		for _, name := range cast {
-			if n, ok := name.(string); ok {
-				names = append(names, n)
-			}
+			names = append(names, name)
 		}
 	}
 

post-processor/shell-local/artifact.go

@@ -0,0 +1,34 @@
+package shell_local
+
+type Artifact struct {
+	builderId string
+	stringVal string
+	destroy   func() error
+	files     []string
+	id        string
+	state     func(name string) interface{}
+}
+
+func (a *Artifact) BuilderId() string {
+	return a.builderId
+}
+
+func (a *Artifact) Files() []string {
+	return a.files
+}
+
+func (a *Artifact) Id() string {
+	return a.id
+}
+
+func (a *Artifact) String() string {
+	return a.stringVal
+}
+
+func (a *Artifact) State(name string) interface{} {
+	return a.state(name)
+}
+
+func (a *Artifact) Destroy() error {
+	return a.destroy()
+}

post-processor/shell-local/post-processor.go

@@ -54,6 +54,18 @@ func (p *PostProcessor) PostProcess(ctx context.Context, ui packer.Ui, artifact
 		return nil, false, false, retErr
 	}
 
+	// Return a "copy" of the artifact to keep the previous artifact data
+	// If we don't this, the data will be lost in packer/rpc/post_processor.go
+	// when a new artifact is created from the client.
+	artifact = &Artifact{
+		builderId: artifact.BuilderId(),
+		stringVal: artifact.String(),
+		destroy:   artifact.Destroy,
+		files:     artifact.Files(),
+		id:        artifact.Id(),
+		state:     artifact.State,
+	}
+
 	// Force shell-local pp to keep the input artifact, because otherwise we'll
 	// lose it instead of being able to pass it through. If you want to delete
 	// the input artifact for a shell local pp, use the artifice pp to create a