syntax_data: {"ast_node_type":"other","tokens":[{"end":59,"kind":"keyword","start":0,"text":"if"}]}
source_snippet:             if caller_sig.output() != callee_sig.output() {
context_before:             // (we should probably just accept this by revealing opaques?)
context_after:                 span_bug!(expr.span, "hir typeck should have checked the return type already");