{"ast_node_type":"impl","tokens":[{"end":100,"kind":"keyword","start":0,"text":"//"}]}
        // since return-position impl trait in trait squashes all of the generics from its source fn
        // We use `generics.count() - lifetimes.len()` here instead of `generics.parent_count`
        // into its own generics, so the opaque's "own" params isn't always just lifetimes.