syntax_data: {"ast_node_type":"function","tokens":[{"end":51,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn as_constant(&self) -> Option<&Const<'tcx>> {
context_before: impl<'tcx> TestBranch<'tcx> {
context_after:         if let Self::Constant(v, _) = self { Some(v) } else { None }