syntax_data: {"ast_node_type":"impl","tokens":[{"end":86,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // Unused generic types or consts on an impl get replaced with inference vars,
context_before:     if impl_source.has_non_region_infer() {
context_after:         // but never resolved, causing the return value of a query to contain inference