syntax_data: {"ast_node_type":"other","tokens":[{"end":65,"kind":"keyword","start":0,"text":"\"could"}]}
source_snippet:                 "could not resolve upvar: {var_hir_id:?} + {:?}",
context_before:                 cx.tcx.hir_span(var_hir_id.0),
context_after:                 self.projection