syntax_data: {"ast_node_type":"other","tokens":[{"end":74,"kind":"keyword","start":0,"text":"LetSource::None"}]}
source_snippet:         LetSource::None | LetSource::PlainLet | LetSource::Else => bug!(),
context_before:     match source {
context_after:         LetSource::IfLet | LetSource::ElseIfLet => emit_diag!(IrrefutableLetPatternsIfLet),