syntax_data: {"ast_node_type":"variable","tokens":[{"end":67,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                     let field_ty = ty_field(cx, (ty, layout), idx);
context_before:                 |fields, (idx, _field_def)| {
context_after:                     let field_layout = layout_of(cx, field_ty)?;