gapi: Add a prefix variable in case we want to namespace on disk

This could get passed through to use as a module download path.

gapi/gapi.go

@@ -50,6 +50,7 @@ type Data struct {
 	Noop          bool
 	NoConfigWatch bool
 	NoStreamWatch bool
+	Prefix        string
 	Debug         bool
 	Logf          func(format string, v ...interface{})
 	// NOTE: we can add more fields here if needed by GAPI endpoints

lang/interpolate.go

@@ -38,6 +38,9 @@ type Pos struct {
 // InterpolateInfo contains some information passed around during interpolation.
 // TODO: rename to Info if this is moved to its own package.
 type InterpolateInfo struct {
+	// Prefix used for path namespacing if required.
+	Prefix string
+
 	// Debug represents if we're running in debug mode or not.
 	Debug bool
 
@@ -73,7 +76,8 @@ func InterpolateStr(str string, pos *Pos, info *InterpolateInfo) (interfaces.Exp
 	}
 
 	transformInfo := &InterpolateInfo{
-		Debug: info.Debug,
+		Prefix: info.Prefix,
+		Debug:  info.Debug,
 		Logf: func(format string, v ...interface{}) {
 			info.Logf("transform: "+format, v...)
 		},

lang/lang.go

@@ -47,6 +47,7 @@ type Lang struct {
 	Input    io.Reader // os.Stdin or anything that satisfies this interface
 	Hostname string
 	World    engine.World
+	Prefix   string
 	Debug    bool
 	Logf     func(format string, v ...interface{})
 

lib/main.go

@@ -481,6 +481,7 @@ func (obj *Main) Run() error {
 					//NoWatch:  obj.NoWatch,
 					NoConfigWatch: obj.NoConfigWatch,
 					NoStreamWatch: obj.NoStreamWatch,
+					Prefix:        fmt.Sprintf("%s/", path.Join(prefix, "gapi")),
 					Debug:         obj.Flags.Debug,
 					Logf: func(format string, v ...interface{}) {
 						log.Printf("gapi: "+format, v...)