document redirects

packer/plugin.go

@@ -25,6 +25,15 @@ type PluginConfig struct {
 	PostProcessors     PostProcessorSet
 	DataSources        DatasourceSet
 
+	// Redirects are only set when a plugin was completely moved out; they allow
+	// telling where a plugin has moved by checking if a known component of this
+	// plugin is used. For example implicitly require the
+	// github.com/hashicorp/amazon plugin if it was moved out and the
+	// "amazon-ebs" plugin is used, but not found.
+	//
+	// Redirects will be bypassed if the redirected components are already found
+	// in their corresponding sets (Builders, Provisioners, PostProcessors,
+	// DataSources)
 	BuilderRedirects       map[string]string
 	DatasourceRedirects    map[string]string
 	ProvisionerRedirects   map[string]string