Fix duplicated channel's name error (#24080)

* Fix duplicated channel's name error

* Test the SQL store layer instead of the API layer

* Remove unused variable and query

server/channels/store/sqlstore/channel_store.go

@@ -778,12 +778,7 @@ func (s SqlChannelStore) updateChannelT(transaction *sqlxTxWrapper, channel *mod
 		WHERE Id=:Id`, channel)
 	if err != nil {
 		if IsUniqueConstraintError(err, []string{"Name", "channels_name_teamid_key"}) {
-			dupChannel := model.Channel{}
-			s.GetReplicaX().Get(&dupChannel, "SELECT * FROM Channels WHERE TeamId = :TeamId AND Name= :Name AND DeleteAt > 0", map[string]any{"TeamId": channel.TeamId, "Name": channel.Name})
-			if dupChannel.DeleteAt > 0 {
-				return nil, store.NewErrInvalidInput("Channel", "Id", channel.Id)
-			}
-			return nil, store.NewErrInvalidInput("Channel", "Id", channel.Id)
+			return nil, store.NewErrInvalidInput("Channel", "Name", channel.Name)
 		}
 		return nil, errors.Wrapf(err, "failed to update channel with id=%s", channel.Id)
 	}

server/channels/store/storetest/channel_store.go

@@ -351,6 +351,13 @@ func testChannelStoreUpdate(t *testing.T, ss store.Store) {
 	o2.Name = o1.Name
 	_, err = ss.Channel().Update(&o2)
 	require.Error(t, err, "update should have failed because of existing name")
+
+	// Make sure that the error correctly reports the wrong field to be Name
+	// See https://mattermost.atlassian.net/browse/MM-53756
+	var invalidInputErr *store.ErrInvalidInput
+	require.ErrorAs(t, err, &invalidInputErr)
+	require.Equal(t, invalidInputErr.Entity, "Channel")
+	require.Equal(t, invalidInputErr.Field, "Name")
 }
 
 func testGetChannelUnread(t *testing.T, ss store.Store) {