syntax_data: {"ast_node_type":"variable","tokens":[{"end":66,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let let_source = match ex.span.desugaring_kind() {
context_before:                 // Give a specific `let_source` for the condition.
context_after:                     Some(DesugaringKind::WhileLoop) => LetSource::WhileLet,