syntax_data: {"ast_node_type":"other","tokens":[{"end":42,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:             // FIXME(generic_const_exprs):
context_before:             ty::ConstKind::Placeholder(placeholder) => write!(self, "{placeholder:?}")?,
context_after:             // write out some legible representation of an abstract const?