syntax_data: {"ast_node_type":"variable","tokens":[{"end":82,"kind":"keyword","start":0,"text":"if"}]}
source_snippet:             if let &mut PassMode::Indirect { ref mut attrs, .. } = &mut arg.mode {
context_before:             // value, so it's implicitly immutable.)
context_after:                 // The `deduced_param_attrs` list could be empty if this is a type of function