SERVER-99545 introduced the initial definition of Operation FCV along with logic to parse it, validating that is one of the following values:

• GenericFCV::kLatest
• GenericFCV::kLastContinuous
• GenericFCV::kLastLTS
• GenericFCV::kUpgradingFromLastLTSToLatest
• GenericFCV::kDowngradingFromLatestToLastLTS
• GenericFCV::kUpgradingFromLastContinuousToLatest
• GenericFCV::kDowngradingFromLatestToLastContinuous
• GenericFCV::kUpgradingFromLastLTSToLastContinuous

However, this logic has a flaw: When LastLTS == LastContinuous, then GenericFCV::kUpgradingFromLastLTSToLastContinuous is an alias for FeatureCompatibilityVersion::kInvalid. This makes the parser accept the string "invalid" as a valid OFCV value.

Furthermore, kUpgradingFromLastLTSToLatest and kUpgradingFromLastContinuousToLatest may be aliases, which makes the returned message contain duplicate values:

{
	"ok" : 0,
	"errmsg" : "Invalid feature compatibility version value 'asdas'. Expected one of the following versions: ''8.1', '8.0', '8.0', 'upgrading from 8.0 to 8.1', 'downgrading from 8.1 to 8.0', 'upgrading from 8.0 to 8.1', 'downgrading from 8.1 to 8.0', 'invalid'",
	"code" : 2,
	"codeName" : "BadValue"
}