{"ast_node_type":"other","tokens":[{"end":82,"kind":"keyword","start":0,"text":"//"}]}
        // E.g. "{0} {0:x} {0} {1}" -> [(0, Display), (0, LowerHex), (1, Display)]
        // Create a list of all _unique_ (argument, format trait) combinations.
        let mut argmap = FxIndexSet::default();