syntax_data: {"ast_node_type":"other","tokens":[{"end":10,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         //
context_before:         // relying on projections in the impl-trait-ref.
context_after:         // e.g., `impl<U: Tr, V: Iterator<Item=U>> Foo<<U as Tr>::T> for V`