Add comment that keeping fields is intentional

- Preserving the Type and Metas fields on merge overlay operations is
  intentional in the anticipation that we may need them later for type
checking
- We did not change logic to preserve fields on overlay replace
  operations, but anticipate we may need to preserve some fields later
on.
Signed-off-by: John Ryan <[email protected]>

pkg/yttlibrary/overlay/array.go

@@ -42,6 +42,7 @@ func (o Op) mergeArrayItem(
 			}
 		}
 		if replace {
+			// left side type and metas are preserved
 			err := leftArray.Items[leftIdx].SetValue(newItem.Value)
 			if err != nil {
 				return err
@@ -116,6 +117,8 @@ func (o Op) replaceArrayItem(
 			return err
 		}
 
+		// left side fields are not preserved.
+		// probably need to rethink how to merge left and right once those fields are needed
 		leftArray.Items[leftIdx] = newItem.DeepCopy()
 		err = leftArray.Items[leftIdx].SetValue(newVal)
 		if err != nil {

pkg/yttlibrary/overlay/map.go

@@ -43,6 +43,7 @@ func (o Op) mergeMapItem(leftMap *yamlmeta.Map, newItem *yamlmeta.MapItem,
 			}
 		}
 		if replace {
+			// left side type and metas are preserved
 			err := leftMap.Items[leftIdx].SetValue(newItem.Value)
 			if err != nil {
 				return err
@@ -115,6 +116,8 @@ func (o Op) replaceMapItem(leftMap *yamlmeta.Map, newItem *yamlmeta.MapItem,
 			return err
 		}
 
+		// left side fields are not preserved.
+		// probably need to rethink how to merge left and right once those fields are needed
 		leftMap.Items[leftIdx] = newItem.DeepCopy()
 		err = leftMap.Items[leftIdx].SetValue(newVal)
 		if err != nil {