We need to document the new error will be raised during running "addShard" command if DWCF (default write concern formula) =w:1 and no CWWC (Clsuter wide write concern) is set
The config server could request the replica set's config as part of the validation in _validateHostAsShard to be able to see what the result of the DWCF would be.
This might be unnecessary depending on the implementation for SERVER-56844.
[BACKPORT] [v5.0] Fail addShard if DWCF=w:1 and no CWWC is set
Fail addShard if DWCF=w:1 and no CWWC is set
Investigate changes in SERVER-56844: Fassert shard server on startup if DWCF=w:1 and no CWWC set
[SERVER] Investigate changes in SERVER-56846: Fail reconfig for shard server if it would change DWCF and CWWC is not set