syntax_data: {"ast_node_type":"other","tokens":[{"end":42,"kind":"keyword","start":0,"text":"($user_value:ident){$($pout:tt)*};"}]}
source_snippet:         ($user_value:ident){$($pout:tt)*};
context_before:         {$($variant:tt($substruct_enum:tt))*},
context_after:     ) => {