syntax_data: {"ast_node_type":"other","tokens":[{"end":78,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:             // MIR building then picks the right MIR casts based on the types.
context_before:             // Default to `ExprKind::Cast` for all explicit casts.
context_after:             ExprKind::Cast { source: self.mirror_expr(source) }