syntax_data: {"ast_node_type":"other","tokens":[{"end":39,"kind":"keyword","start":0,"text":"Pair(ArgAttributes,"}]}
source_snippet:     Pair(ArgAttributes, ArgAttributes),
context_before:     /// The argument has a layout abi of `ScalarPair`.
context_after:     /// Pass the argument after casting it. See the `CastTarget` docs for details.