syntax_data: {"ast_node_type":"other","tokens":[{"end":79,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // The "retagging" transformation (for Stacked Borrows) relies on this.
context_before:         // the index changing later: Nothing will ever change this temporary.
context_after:         let idx = unpack!(block = self.as_temp(block, temp_lifetime, index, Mutability::Not));