syntax_data: {"ast_node_type":"other","tokens":[{"end":48,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// instead of `fn(ty) -> T with T = isize`.
context_before:     /// ask for the type of `id` in `id(3)`, it will return `fn(&isize) -> isize`
context_after:     pub fn expr_ty(&self, expr: &hir::Expr<'_>) -> Ty<'tcx> {