syntax_data: {"ast_node_type":"other","tokens":[{"end":55,"kind":"keyword","start":0,"text":"visit::walk_expr(&mut"}]}
source_snippet:     visit::walk_expr(&mut is_poly_vis, &body[body_id]);
context_before:     let mut is_poly_vis = IsThirPolymorphic { is_poly: false, thir: body };
context_after:     if !is_poly_vis.is_poly {