syntax_data: {"ast_node_type":"other","tokens":[{"end":79,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:             // Subtype(&'a u8, &'b u8) => Outlives('a: 'b) => SubRegion('b, 'a)
context_before:         match self.ambient_variance {
context_after:             ty::Covariant => self.infcx.sub_regions(b, a, self.span),