feat: Add support for using highlight without returning the field as the output field.

internal/proxy/highlighter.go

@@ -36,6 +36,7 @@ const (
 
 type Highlighter interface {
 	AsSearchPipelineOperator(t *searchTask) (operator, error)
+	FieldIDs() []int64
 }
 
 // highlight task for one field
@@ -114,18 +115,26 @@ func (h *LexicalHighlighter) addTaskWithQuery(fieldID int64, query *highlightQue
 	})
 }
 
-func (h *LexicalHighlighter) AsSearchPipelineOperator(t *searchTask) (operator, error) {
+func (h *LexicalHighlighter) initHighlightQueries(t *searchTask) error {
 	// add query to highlight tasks
 	for _, query := range h.queries {
 		fieldID, ok := t.schema.MapFieldID(query.fieldName)
 		if !ok {
-			return nil, merr.WrapErrParameterInvalidMsg("highlight field not found in schema: %s", query.fieldName)
+			return merr.WrapErrParameterInvalidMsg("highlight field not found in schema: %s", query.fieldName)
 		}
 		h.addTaskWithQuery(fieldID, query)
 	}
+	return nil
+}
+
+func (h *LexicalHighlighter) AsSearchPipelineOperator(t *searchTask) (operator, error) {
 	return newLexicalHighlightOperator(t, lo.Values(h.tasks))
 }
 
+func (h *LexicalHighlighter) FieldIDs() []int64 {
+	return lo.Keys(h.tasks)
+}
+
 func NewLexicalHighlighter(highlighter *commonpb.Highlighter) (*LexicalHighlighter, error) {
 	params := funcutil.KeyValuePair2Map(highlighter.GetParams())
 	h := &LexicalHighlighter{

internal/proxy/task_search.go

@@ -602,7 +602,12 @@ func (t *searchTask) createLexicalHighlighter(highlighter *commonpb.Highlighter,
 		if err != nil {
 			return err
 		}
-		return h.addTaskWithSearchText(fieldId, fieldName, analyzerName, texts)
+		err = h.addTaskWithSearchText(fieldId, fieldName, analyzerName, texts)
+		if err != nil {
+			return err
+		}
+
+		return h.initHighlightQueries(t)
 	}
 	return nil
 }
@@ -642,10 +647,24 @@ func (t *searchTask) initSearchRequest(ctx context.Context) error {
 		}
 	}
 
+	analyzer, err := funcutil.GetAttrByKeyFromRepeatedKV(AnalyzerKey, t.request.GetSearchParams())
+	if err == nil {
+		t.SearchRequest.AnalyzerName = analyzer
+	}
+
 	t.isIterator = isIterator
 	t.SearchRequest.Offset = offset
 	t.SearchRequest.FieldId = queryInfo.GetQueryFieldId()
 
+	if err := t.addHighlightTask(t.request.GetHighlighter(), queryInfo.GetMetricType(), queryInfo.GetQueryFieldId(), t.request.GetPlaceholderGroup(), t.SearchRequest.GetAnalyzerName()); err != nil {
+		return err
+	}
+
+	// add highlight field ids to output fields id
+	if t.highlighter != nil {
+		t.SearchRequest.OutputFieldsId = append(t.SearchRequest.OutputFieldsId, t.highlighter.FieldIDs()...)
+	}
+
 	if t.partitionKeyMode {
 		// isolation has tighter constraint, check first
 		mvErr := setQueryInfoIfMvEnable(queryInfo, t, plan)
@@ -696,16 +715,6 @@ func (t *searchTask) initSearchRequest(ctx context.Context) error {
 	t.SearchRequest.GroupByFieldId = queryInfo.GroupByFieldId
 	t.SearchRequest.GroupSize = queryInfo.GroupSize
 
-	if t.SearchRequest.MetricType == metric.BM25 {
-		analyzer, err := funcutil.GetAttrByKeyFromRepeatedKV(AnalyzerKey, t.request.GetSearchParams())
-		if err == nil {
-			t.SearchRequest.AnalyzerName = analyzer
-		}
-	}
-	if err := t.addHighlightTask(t.request.GetHighlighter(), t.SearchRequest.MetricType, t.SearchRequest.FieldId, t.request.GetPlaceholderGroup(), t.SearchRequest.GetAnalyzerName()); err != nil {
-		return err
-	}
-
 	if embedding.HasNonBM25Functions(t.schema.CollectionSchema.Functions, []int64{queryInfo.GetQueryFieldId()}) {
 		ctx, sp := otel.Tracer(typeutil.ProxyRole).Start(ctx, "Proxy-Search-call-function-udf")
 		defer sp.End()