syntax_data: {"ast_node_type":"other","tokens":[{"end":69,"kind":"keyword","start":0,"text":"ty::Covariant"}]}
source_snippet:             ty::Covariant => self.infcx.sub_regions(b, a, self.span),
context_before:             // Subtype(&'a u8, &'b u8) => Outlives('a: 'b) => SubRegion('b, 'a)
context_after:             // Suptype(&'a u8, &'b u8) => Outlives('b: 'a) => SubRegion('a, 'b)