syntax_data: {"ast_node_type":"other","tokens":[{"end":76,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // When we instantiate, say, `V => IntoIter<u32>, U => $0`, the last
context_before:         //    <U as Iterator>::Item: Copy
context_after:         // obligation will normalize to `<$0 as Iterator>::Item = $1` and