syntax_data: {"ast_node_type":"other","tokens":[{"end":72,"kind":"keyword","start":0,"text":"Some(\"thunk-extern\")"}]}
source_snippet:             Some("thunk-extern") => *slot = FunctionReturn::ThunkExtern,
context_before:             Some("keep") => *slot = FunctionReturn::Keep,
context_after:             _ => return false,