Log instead of error for term diff bug (#27424)

GitOrigin-RevId: 32543f38e09af04528d9e3a6730e2b532017840d

Author: emmaling27

crates/search/src/memory_index/mod.rs

@@ -481,10 +481,16 @@ impl MemorySearchIndex {
                             );
                             0
                         });
-                } else if field == &Field::from_field_id(SEARCH_FIELD_ID) {
-                    stats
-                        .num_terms_by_field
-                        .insert(*field, (*total_term_diff as i64).try_into()?);
+                } else {
+                    let total_term_diff =
+                        (*total_term_diff as i64).try_into().unwrap_or_else(|e| {
+                            tracing::warn!(
+                                "Inserting 0 for num_terms for field {field:?} with \
+                                 {total_term_diff} and error {e}"
+                            );
+                            0
+                        });
+                    stats.num_terms_by_field.insert(*field, total_term_diff);
                 }
             }
             for (term, term_id) in &term_ids {

crates/search/src/searcher/searcher.rs

@@ -958,7 +958,7 @@ impl<RT: Runtime> SearcherImpl<RT> {
                             // Tantivy's total_num_tokens count is only approximate, so we can't guarantee this won't underflow.
                             .unwrap_or_else(|| {
                                 tracing::warn!(
-                                    "num_terms underflowed for field {field:?}, subtracted num_terms_deleted: {num_terms_deleted} from \
+                                    "num_terms underflowed for field {field:?} in query_bm_25_stats_impl, subtracted num_terms_deleted: {num_terms_deleted} from \
                                     total_num_tokens: {total_num_tokens}"
                                 );
                                 0
@@ -971,6 +971,9 @@ impl<RT: Runtime> SearcherImpl<RT> {
                     num_documents,
                     doc_frequencies,
                 };
+                if stats.is_empty() {
+                    tracing::warn!("Empty BM25 stats");
+                }
                 Ok(stats)
             },
         }
@@ -1360,6 +1363,12 @@ impl Bm25Stats {
             doc_frequencies: BTreeMap::new(),
         }
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.num_terms_by_field.is_empty()
+            && self.num_documents == 0
+            && self.doc_frequencies.is_empty()
+    }
 }
 
 impl Add for Bm25Stats {