syntax_data: {"ast_node_type":"variable","tokens":[{"end":28,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// let ty: Ty<I> = ...;
context_before:     /// let a: Canonical<I, T> = ...;
context_after:     /// let b: Canonical<I, (T, Ty<I>)> = a.unchecked_map(|v| (v, ty));