syntax_data: {"ast_node_type":"other","tokens":[{"end":71,"kind":"keyword","start":0,"text":"imported_src_file.external_src.borrow().get_source().is_none(),"}]}
source_snippet:         imported_src_file.external_src.borrow().get_source().is_none(),
context_before:     assert!(
context_after:         "imported source file should not have source yet"