Fix panic when changing archetype files when servere is running

Fixes gohugoio#12195

Author: bep

hugolib/hugo_sites_build.go

@@ -792,6 +792,8 @@ func (h *HugoSites) processPartial(ctx context.Context, l logg.LevelLogger, conf
 			// It's hard to determine the exact change set of this,
 			// so be very coarse grained for now.
 			changes = append(changes, identity.GenghisKhan)
+		case files.ComponentFolderArchetypes:
+			// Ignore for now.
 		default:
 			panic(fmt.Sprintf("unknown component: %q", pathInfo.Component()))
 		}

hugolib/rebuild_test.go

@@ -1472,3 +1472,21 @@ all: {{ $ab.RelPermalink }}
 	b.AddFiles("assets/common/c3.css", "c3").Build()
 	b.AssertFileContent("public/ab.css", "abc1c2 editedc3")
 }
+
+func TestRebuildEditArchetypeFile(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+baseURL = "https://example.com"
+disableLiveReload = true
+-- archetypes/default.md --
+---
+title: "Default"
+---
+`
+
+	b := TestRunning(t, files)
+	// Just make sure that it doesn't panic.
+	b.EditFileReplaceAll("archetypes/default.md", "Default", "Default Edited").Build()
+}