Fix dashboard migration discrepancies between backend and frontend implementations (use toEqual) (#110268)

**Highlights**

* **Single-version migrations**: add `targetVersion` to migrator & model, separate outputs, enforce exact version.
* **Datasource fixes**: include `apiVersion` in tests, empty-string → `{}`, preserve `{}` refs, drop unwanted defaults.
* **Panel defaults & nesting**: only top-level panels get defaults; preserve empty `transformations` context-aware; filter repeated panels.

* **Migration parity**

  * V16: collapsed rows, grid height parsing (`px`).
  * V17: omit `maxPerRow` when `minSpan=1`.
  * V19–V20: cleanup defaults (`targetBlank`, style).
  * V23–V24: template vars + table panel consistency.
  * V28: full singlestat/stat parity, mappings & color.
  * V30–V36: threshold logic, empty refs, nested targets.
* **Save-model cleanup**: replicate frontend defaults/filtering, drop null IDs, metadata, unused props.
* **Testing**: unified suites, dev dashboards (v42), full unit coverage for major migrations.

Co-authored-by: Ivan Ortega [ivanortegaalba@gmail.com](mailto:ivanortegaalba@gmail.com)
Co-authored-by: Dominik Prokop [dominik.prokop@grafana.com](mailto:dominik.prokop@grafana.com)

apps/dashboard/pkg/migration/migrate.go

@@ -13,6 +13,15 @@ func Initialize(dsInfoProvider schemaversion.DataSourceInfoProvider) {
 	migratorInstance.init(dsInfoProvider)
 }
 
+// ResetForTesting resets the migrator singleton for testing purposes.
+func ResetForTesting() {
+	migratorInstance = &migrator{
+		migrations: map[int]schemaversion.SchemaVersionMigrationFunc{},
+		ready:      make(chan struct{}),
+	}
+	initOnce = sync.Once{}
+}
+
 // Migrate migrates the given dashboard to the target version.
 // This will block until the migrator is initialized.
 func Migrate(ctx context.Context, dash map[string]interface{}, targetVersion int) error {
@@ -47,6 +56,51 @@ func (m *migrator) migrate(ctx context.Context, dash map[string]interface{}, tar
 	// wait for the migrator to be initialized
 	<-m.ready
 
+	// 0. Clean up dashboard properties that frontend never includes in save model
+	// These properties are added by backend but frontend filters them out
+	delete(dash, "__elements")
+	delete(dash, "__inputs")
+	delete(dash, "__requires")
+
+	// 1. Track which panels had transformations in original input (before any defaults applied)
+	// This is needed to match frontend hasOwnProperty behavior
+	trackOriginalTransformations(dash)
+
+	// 2. Apply ALL frontend defaults FIRST (DashboardModel + PanelModel defaults)
+	// This replicates the behavior of the frontend DashboardModel and PanelModel constructors
+	applyFrontendDefaults(dash)
+
+	// 2. Apply panel defaults to ALL panels (both top-level and nested in rows)
+	// The frontend creates PanelModel instances for all panels, including those in rows
+	if dashboardPanels, ok := dash["panels"].([]interface{}); ok {
+		for _, panelInterface := range dashboardPanels {
+			if panel, ok := panelInterface.(map[string]interface{}); ok {
+				applyPanelDefaults(panel)
+			}
+		}
+	}
+
+	// Apply defaults to panels inside rows (for pre-v16 dashboards)
+	// Match frontend upgradeToGridLayout: only panels NOT in collapsed rows get new PanelModel() constructor
+	if rows, ok := dash["rows"].([]interface{}); ok {
+		showRows := shouldShowRows(rows)
+
+		for _, rowInterface := range rows {
+			row, ok := rowInterface.(map[string]interface{})
+			if !ok {
+				continue
+			}
+
+			applyRowPanelDefaults(row, showRows)
+		}
+	}
+
+	// 3. Ensure panel IDs are unique for ALL panels (including nested ones)
+	// This matches the frontend ensurePanelsHaveUniqueIds() behavior
+	ensurePanelsHaveUniqueIds(dash)
+
+	// TODO: Probably we can check if we can migrate at the beginning of the function
+	// 4. Ensure schema version is set and if not default to 0
 	inputVersion := schemaversion.GetSchemaVersion(dash)
 	dash["schemaVersion"] = inputVersion
 
@@ -56,6 +110,8 @@ func (m *migrator) migrate(ctx context.Context, dash map[string]interface{}, tar
 		return schemaversion.NewMinimumVersionError(inputVersion)
 	}
 
+	// 5. Run existing migration pipeline UNCHANGED
+	// (All the existing v28, v29, etc. migrators run exactly as before)
 	for nextVersion := inputVersion + 1; nextVersion <= targetVersion; nextVersion++ {
 		if migration, ok := m.migrations[nextVersion]; ok {
 			if err := migration(ctx, dash); err != nil {
@@ -66,9 +122,58 @@ func (m *migrator) migrate(ctx context.Context, dash map[string]interface{}, tar
 		}
 	}
 
+	// 6. Clean up the dashboard to match frontend getSaveModel behavior
+	// This removes properties that shouldn't be persisted and filters out default values
+	cleanupDashboardForSave(dash)
+
 	if schemaversion.GetSchemaVersion(dash) != targetVersion {
 		return schemaversion.NewMigrationError("schema version not migrated to target version", inputVersion, targetVersion, "")
 	}
 
 	return nil
 }
+
+// shouldShowRows determines if row panels will be created (showRows logic)
+func shouldShowRows(rows []interface{}) bool {
+	for _, rowInterface := range rows {
+		row, ok := rowInterface.(map[string]interface{})
+		if !ok {
+			continue
+		}
+
+		collapse := schemaversion.GetBoolValue(row, "collapse")
+		showTitle := schemaversion.GetBoolValue(row, "showTitle")
+		repeat := schemaversion.GetStringValue(row, "repeat")
+
+		if collapse || showTitle || repeat != "" {
+			return true
+		}
+	}
+	return false
+}
+
+// applyRowPanelDefaults applies panel defaults to panels within a row based on frontend logic
+func applyRowPanelDefaults(row map[string]interface{}, showRows bool) {
+	rowPanels, ok := row["panels"].([]interface{})
+	if !ok {
+		return
+	}
+
+	collapse := schemaversion.GetBoolValue(row, "collapse")
+
+	// Frontend: if (rowPanelModel && rowPanel.collapsed) { push(panel) } else { push(new PanelModel(panel)) }
+	// Only non-collapsed panels get PanelModel defaults (refId: "A", overrides: [], etc.)
+	applyDefaults := !showRows || !collapse
+
+	if !applyDefaults {
+		return
+	}
+
+	for _, panelInterface := range rowPanels {
+		panel, ok := panelInterface.(map[string]interface{})
+		if !ok {
+			continue
+		}
+		applyPanelDefaults(panel)
+	}
+}