internal/rosa: handle nil source

Source is not always required. This improves flexibility.

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

internal/rosa/package/images/package.az

@@ -25,7 +25,6 @@ package system-image {
 	version = unversioned;
 	exclude = true;
 
-	source = earlyinit;
 	extra = [
 		musl,
 		mksh,

internal/rosa/rosa.go

@@ -476,9 +476,6 @@ func (t Toolchain) NewPackage(
 	if name == "" || version == "" {
 		panic("name must be non-empty")
 	}
-	if source == nil {
-		panic("source must be non-nil")
-	}
 	rn := name
 	if version != Unversioned {
 		rn = name + "-" + version
@@ -536,6 +533,17 @@ cd '/usr/src/` + name + `/'
 		panic("cannot remain in root")
 	}
 
+	paths := attr.Paths
+	if source != nil {
+		paths = slices.Concat(attr.Paths, []pkg.ExecPath{
+			pkg.Path(AbsUsrSrc.Append(
+				name+sourceSuffix,
+			), attr.Writable || wantsWrite, t.NewPatchedSource(
+				rn, source, !attr.Chmod && !wantsChmod, attr.Patches...,
+			)),
+		})
+	}
+
 	return t.New(
 		rn,
 		attr.Flag,
@@ -543,13 +551,7 @@ cd '/usr/src/` + name + `/'
 		attr.KnownChecksum,
 		attr.Env,
 		scriptEarly+helper.script(t, name),
-		slices.Concat(attr.Paths, []pkg.ExecPath{
-			pkg.Path(AbsUsrSrc.Append(
-				name+sourceSuffix,
-			), attr.Writable || wantsWrite, t.NewPatchedSource(
-				rn, source, !attr.Chmod && !wantsChmod, attr.Patches...,
-			)),
-		})...,
+		paths...,
 	)
 }
 

internal/rosa/state.go

@@ -1134,10 +1134,12 @@ func (ctx *evalContext) pf(
 		}
 
 	default:
-		panic(azalea.TypeError{
-			Concrete: reflect.TypeOf(sourceA),
-			Asserted: reflect.TypeFor[pkg.Artifact](),
-		})
+		if sourceA != nil {
+			panic(azalea.TypeError{
+				Concrete: reflect.TypeOf(sourceA),
+				Asserted: reflect.TypeFor[pkg.Artifact](),
+			})
+		}
 	}
 
 	v = cachedArtifact{&meta, ctx.t.NewPackage(