syntax_data: {"ast_node_type":"other","tokens":[{"end":61,"kind":"keyword","start":0,"text":"subpattern:"}]}
source_snippet:                 subpattern: Box::new(Pat { span, ty, kind }),
context_before:             kind = PatKind::AscribeUserType {
context_after:                 ascription: Ascription { annotation, variance: ty::Covariant },