syntax_data: {"ast_node_type":"other","tokens":[{"end":76,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:                 // those expressions, so this case is currently unreachable.
context_before:                 // In both cases they are specifically handled by the lowerings of
context_after:                 span_bug!(expr_span, "unexpected let expression outside of if or match-guard");