fix(merge): ensure to have same data type while performing 3-way merge

dynamic/apply/apply.go

@@ -162,45 +162,73 @@ func merge(fieldPath string, observedAsDest, lastApplied, desired interface{}) (
 
 	switch observedDestVal := observedAsDest.(type) {
 	case map[string]interface{}:
+
+		var lastAppliedVal, desiredVal map[string]interface{}
+		var ok bool
 		// In this case, observed is a map.
 		// Make sure the others are maps too.
 		// Nil desired &/ nil last applied are OK.
-		lastAppliedVal, ok := lastApplied.(map[string]interface{})
-		if !ok && lastAppliedVal != nil {
-			return nil,
-				errors.Errorf(
-					"%s: Expecting last applied as map[string]interface{}, got %T",
-					fieldPath, lastApplied,
-				)
+
+		// NOTE: There are chances of having lastApplied field as nil
+		// if observedAsDest fields are autogenerated. If lastApplied is
+		// nil nothing we can do by type asserting.
+		if lastApplied != nil {
+			lastAppliedVal, ok = lastApplied.(map[string]interface{})
+			if !ok {
+				return nil,
+					errors.Errorf(
+						"%s: Expecting last applied as map[string]interface{}, got %T",
+						fieldPath, lastApplied,
+					)
+			}
 		}
-		desiredVal, ok := desired.(map[string]interface{})
-		if !ok && desiredVal != nil {
-			return nil,
-				errors.Errorf(
-					"%s: Expecting desired as map[string]interface{}, got %T",
-					fieldPath, desired,
-				)
+
+		// NOTE: There are chances of having desired field as nil if a caller
+		// doesn't need to update the fields in that path no need for any update
+		if desired != nil {
+			desiredVal, ok = desired.(map[string]interface{})
+			if !ok {
+				return nil,
+					errors.Errorf(
+						"%s: Expecting desired as map[string]interface{}, got %T",
+						fieldPath, desired,
+					)
+			}
 		}
 		return mergeMap(fieldPath, observedDestVal, lastAppliedVal, desiredVal)
 	case []interface{}:
+		var lastAppliedVal, desiredVal []interface{}
+		var ok bool
+
 		// In this case observed is an array.
 		// Make sure desired & last applied are arrays too.
 		// Nil desired &/ last applied are OK.
-		lastAppliedVal, ok := lastApplied.([]interface{})
-		if !ok && lastAppliedVal != nil {
-			return nil,
-				errors.Errorf(
-					"%s: Expecting last applied as []interface{}, got %T",
-					fieldPath, lastApplied,
-				)
+
+		// NOTE: There are chances of having lastApplied field as nil
+		// if observedAsDest fields are autogenerated. If lastApplied is
+		// nil nothing we can do by type asserting.
+		if lastApplied != nil {
+			lastAppliedVal, ok = lastApplied.([]interface{})
+			if !ok {
+				return nil,
+					errors.Errorf(
+						"%s: Expecting last applied as []interface{}, got %T",
+						fieldPath, lastApplied,
+					)
+			}
 		}
-		desiredVal, ok := desired.([]interface{})
-		if !ok && desiredVal != nil {
-			return nil,
-				fmt.Errorf(
-					"%s: Expecting desired as []interface{}, got %T",
-					fieldPath, desired,
-				)
+
+		// NOTE: There are chances of having desired field as nil if a caller
+		// doesn't need to update the fields in that path no need for any update
+		if desired != nil {
+			desiredVal, ok = desired.([]interface{})
+			if !ok {
+				return nil,
+					fmt.Errorf(
+						"%s: Expecting desired as []interface{}, got %T",
+						fieldPath, desired,
+					)
+			}
 		}
 		return mergeArray(fieldPath, observedDestVal, lastAppliedVal, desiredVal)
 	default: