syntax_data: {"ast_node_type":"other","tokens":[{"end":83,"kind":"keyword","start":0,"text":"add_feature_diagnostics_for_issue(&mut"}]}
source_snippet:     add_feature_diagnostics_for_issue(&mut err, sess, feature, issue, false, None);
context_before:     let mut err = sess.dcx().struct_span_warn(span, explain);