syntax_data: {"ast_node_type":"variable","tokens":[{"end":18,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let mut i = 0;
context_before: fn cast_target(cls: &[Option<Class>], size: Size) -> CastTarget {
context_after:     let lo = reg_component(cls, &mut i, size).unwrap();