syntax_data: {"ast_node_type":"other","tokens":[{"end":56,"kind":"keyword","start":0,"text":"existing_drops_map:"}]}
source_snippet:     existing_drops_map: FxHashMap<DropNodeKey, DropIdx>,
context_before:     /// Map for finding the index of an existing node, given its contents.
context_after:     /// Edges into the `DropTree` that need to be added once it's lowered.