added InvertedIndexReader::doc_freq_async and SnippetGenerator::new methods

src/core/inverted_index_reader.rs

@@ -230,4 +230,13 @@ impl InvertedIndexReader {
         }
         Ok(())
     }
+
+    /// Returns the number of documents containing the term asynchronously.
+    pub async fn doc_freq_async(&self, term: &Term) -> crate::AsyncIoResult<u32> {
+        Ok(self
+            .get_term_info_async(term)
+            .await?
+            .map(|term_info| term_info.doc_freq)
+            .unwrap_or(0u32))
+    }
 }

src/core/searcher.rs

@@ -134,6 +134,19 @@ impl Searcher {
         Ok(total_doc_freq)
     }
 
+    /// Return the overall number of documents containing
+    /// the given term in an asynchronous manner.
+    #[cfg(feature = "quickwit")]
+    pub async fn doc_freq_async(&self, term: &Term) -> crate::Result<u64> {
+        let mut total_doc_freq = 0;
+        for segment_reader in &self.inner.segment_readers {
+            let inverted_index = segment_reader.inverted_index(term.field())?;
+            let doc_freq = inverted_index.doc_freq_async(term).await?;
+            total_doc_freq += u64::from(doc_freq);
+        }
+        Ok(total_doc_freq)
+    }
+
     /// Return the list of segment readers
     pub fn segment_readers(&self) -> &[SegmentReader] {
         &self.inner.segment_readers