cmd/app: multiple template uppers

Having multiple environments is useful, and this was trivial to implement.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/app/app.go

@@ -35,6 +35,10 @@ func parse(id string, base *check.Absolute, r io.Reader) (*hst.Config, error) {
 	shell := fhs.AbsRoot.Append("bin", "zsh")
 	home := hst.AbsPrivateTmp.Append("home")
 
+	root := hst.FSOverlay{
+		Target: fhs.AbsRoot,
+		Lower:  []*check.Absolute{base.Append("initial")},
+	}
 	c := hst.Config{
 		ID:          id,
 		Enablements: new(hst.Enablements),
@@ -51,13 +55,7 @@ func parse(id string, base *check.Absolute, r io.Reader) (*hst.Config, error) {
 		Container: &hst.ContainerConfig{
 			Env: make(map[string]string),
 			Filesystem: []hst.FilesystemConfigJSON{
-				{FilesystemConfig: &hst.FSOverlay{
-					Target: fhs.AbsRoot,
-					Lower: []*check.Absolute{
-						base.Append("template", "initial"),
-					},
-					Upper: base.Append("template", "upper"),
-				}},
+				{FilesystemConfig: &root},
 				{FilesystemConfig: &hst.FSBind{
 					Target: home,
 					Source: base.Append("state", id),
@@ -102,10 +100,13 @@ func parse(id string, base *check.Absolute, r io.Reader) (*hst.Config, error) {
 	if err := scanOnce(); err != nil {
 		return nil, err
 	}
-	if v, err := strconv.Atoi(s.Text()); err != nil {
+	if template, identity, ok := strings.Cut(s.Text(), ":"); !ok {
+		return nil, io.ErrUnexpectedEOF
+	} else if v, err := strconv.Atoi(identity); err != nil {
 		return nil, err
 	} else {
 		c.Identity = v
+		root.Upper = base.Append("template", template, "upper")
 	}
 
 	if err := scanOnce(); err != nil {