seed: return snap types as specified by the model for essential snaps

this information is available, no reason for code using seed to have
to find it again (typically having to open the snaps)

seed/helpers.go

@@ -100,3 +100,20 @@ func readInfo(snapPath string, si *snap.SideInfo) (*snap.Info, error) {
 	}
 	return snap.ReadInfoFromSnapFile(snapf, si)
 }
+
+func snapTypeFromModel(modSnap *asserts.ModelSnap) snap.Type {
+	switch modSnap.SnapType {
+	case "base":
+		return snap.TypeBase
+	case "core":
+		return snap.TypeOS
+	case "gadget":
+		return snap.TypeGadget
+	case "kernel":
+		return snap.TypeKernel
+	case "snapd":
+		return snap.TypeSnapd
+	default:
+		return snap.TypeApp
+	}
+}

seed/seed.go

@@ -40,6 +40,10 @@ type Snap struct {
 
 	SideInfo *snap.SideInfo
 
+	// EssentialType is the type of the snap as specified by the model.
+	// Provided only for essential snaps (Essential = true).
+	EssentialType snap.Type
+
 	Essential bool
 	Required  bool
 

seed/seed16.go

@@ -196,7 +196,7 @@ func (s *seed16) LoadMeta(tm timings.Measurer) error {
 	}
 
 	// add the essential snaps
-	addEssential := func(snapName string, pinnedTrack string) (*Snap, error) {
+	addEssential := func(snapName string, pinnedTrack string, essType snap.Type) (*Snap, error) {
 		// be idempotent
 		if added[snapName] {
 			return nil, nil
@@ -211,6 +211,11 @@ func (s *seed16) LoadMeta(tm timings.Measurer) error {
 			return nil, err
 		}
 
+		if essType == snap.TypeBase && snapName == "core" {
+			essType = snap.TypeOS
+		}
+
+		seedSnap.EssentialType = essType
 		seedSnap.Essential = true
 		seedSnap.Required = true
 		added[snapName] = true
@@ -222,25 +227,25 @@ func (s *seed16) LoadMeta(tm timings.Measurer) error {
 	if len(yamlSnaps) != 0 {
 		// ensure "snapd" snap is installed first
 		if model.Base() != "" || classicWithSnapd {
-			if _, err := addEssential("snapd", ""); err != nil {
+			if _, err := addEssential("snapd", "", snap.TypeSnapd); err != nil {
 				return err
 			}
 		}
 		if !classicWithSnapd {
-			if _, err := addEssential(baseSnap, ""); err != nil {
+			if _, err := addEssential(baseSnap, "", snap.TypeBase); err != nil {
 				return err
 			}
 		}
 	}
 
 	if kernelName := model.Kernel(); kernelName != "" {
-		if _, err := addEssential(kernelName, model.KernelTrack()); err != nil {
+		if _, err := addEssential(kernelName, model.KernelTrack(), snap.TypeKernel); err != nil {
 			return err
 		}
 	}
 
 	if gadgetName := model.Gadget(); gadgetName != "" {
-		gadget, err := addEssential(gadgetName, model.GadgetTrack())
+		gadget, err := addEssential(gadgetName, model.GadgetTrack(), snap.TypeGadget)
 		if err != nil {
 			return err
 		}
@@ -260,7 +265,7 @@ func (s *seed16) LoadMeta(tm timings.Measurer) error {
 		if baseSnap != "" && gadgetBase != baseSnap {
 			return fmt.Errorf("cannot use gadget snap because its base %q is different from model base %q", gadgetBase, model.Base())
 		}
-		if _, err = addEssential(gadgetBase, ""); err != nil {
+		if _, err = addEssential(gadgetBase, "", snap.TypeBase); err != nil {
 			return err
 		}
 	}