MM-11725: Add specific autocomplete endpoint for search autocomplete (#9337)

store/sqlstore/channel_store.go

@@ -1589,6 +1589,53 @@ func (s SqlChannelStore) AutocompleteInTeam(teamId string, term string, includeD
 	})
 }
 
+func (s SqlChannelStore) AutocompleteInTeamForSearch(teamId string, userId string, term string, includeDeleted bool) store.StoreChannel {
+	return store.Do(func(result *store.StoreResult) {
+		deleteFilter := "AND DeleteAt = 0"
+		if includeDeleted {
+			deleteFilter = ""
+		}
+
+		queryFormat := `
+			SELECT
+				C.*
+			FROM
+				Channels AS C
+			JOIN
+				ChannelMembers AS CM ON CM.ChannelId = C.Id
+			WHERE
+			    C.TeamId = :TeamId
+				AND CM.UserId = :UserId
+				` + deleteFilter + `
+				%v
+			LIMIT 50`
+
+		var channels model.ChannelList
+
+		if likeClause, likeTerm := s.buildLIKEClause(term); likeClause == "" {
+			if _, err := s.GetReplica().Select(&channels, fmt.Sprintf(queryFormat, ""), map[string]interface{}{"TeamId": teamId, "UserId": userId}); err != nil {
+				result.Err = model.NewAppError("SqlChannelStore.AutocompleteInTeamForSearch", "store.sql_channel.search.app_error", nil, "term="+term+", "+", "+err.Error(), http.StatusInternalServerError)
+			}
+		} else {
+			// Using a UNION results in index_merge and fulltext queries and is much faster than the ref
+			// query you would get using an OR of the LIKE and full-text clauses.
+			fulltextClause, fulltextTerm := s.buildFulltextClause(term)
+			likeQuery := fmt.Sprintf(queryFormat, "AND "+likeClause)
+			fulltextQuery := fmt.Sprintf(queryFormat, "AND "+fulltextClause)
+			query := fmt.Sprintf("(%v) UNION (%v) LIMIT 50", likeQuery, fulltextQuery)
+
+			if _, err := s.GetReplica().Select(&channels, query, map[string]interface{}{"TeamId": teamId, "UserId": userId, "LikeTerm": likeTerm, "FulltextTerm": fulltextTerm}); err != nil {
+				result.Err = model.NewAppError("SqlChannelStore.AutocompleteInTeamForSearch", "store.sql_channel.search.app_error", nil, "term="+term+", "+", "+err.Error(), http.StatusInternalServerError)
+			}
+		}
+
+		sort.Slice(channels, func(a, b int) bool {
+			return strings.ToLower(channels[a].DisplayName) < strings.ToLower(channels[b].DisplayName)
+		})
+		result.Data = &channels
+	})
+}
+
 func (s SqlChannelStore) SearchInTeam(teamId string, term string, includeDeleted bool) store.StoreChannel {
 	return store.Do(func(result *store.StoreResult) {
 		deleteFilter := "AND DeleteAt = 0"