syntax_data: {"ast_node_type":"other","tokens":[{"end":48,"kind":"keyword","start":0,"text":"tcx.def_span(impl_.impl_def_id),"}]}
source_snippet:                 tcx.def_span(impl_.impl_def_id),
context_before:             ImplSource::UserDefined(impl_) => tcx.dcx().span_delayed_bug(
context_after:                 "this impl has unconstrained generic parameters",