syntax_data: {"ast_node_type":"other","tokens":[{"end":81,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:                 // `pat` should be `Some(<pat_field>)` from a desugared for loop.
context_before:                 let pat = &self.thir[snd_arm].pattern;
context_after:                 debug_assert_eq!(pat.span.desugaring_kind(), Some(DesugaringKind::ForLoop));