Given

Check that all positioned items in this tree satisfy the following conditions:

• Parent spans contain child spans
• If item is a non-empty tree, it has a position

Clone this node but assign it a fresh id which marks it as a node in file.

The union of startSpan and the spans of all positioned children that have the same source as this node, except that Inlined nodes only consider their call child.

Side effect: Any descendants without spans have but with the same source as this node have their span set to the end position of the envelope of all children to the left, or, if that one does not exist, to the start position of the envelope of all children to the right.

The span part of the item's position

This positioned item, widened to SrcPos. Used to make clear we only need the position, typically for error reporting.

A unique identifier in case -Yshow-tree-ids, or -Ydebug-tree-with-id is set, -1 otherwise.

A positioned item like this one with given span. If the positioned item is source-derived, a clone is returned. If the positioned item is synthetic, the position is updated destructively and the item itself is returned.