syntax_data: {"ast_node_type":"other","tokens":[{"end":54,"kind":"keyword","start":0,"text":"expr:"}]}
source_snippet:                 expr: self.mirror_expr(let_expr.init),
context_before:             hir::ExprKind::Let(let_expr) => ExprKind::Let {
context_after:                 pat: self.pattern_from_hir(let_expr.pat),