git-annex adjust --lock-missing

Like --hide-missing the branch does not get updated when content
availability changes.

Seems to basically work, but sync does not update it yet.

Also, when a file is present and so unlocked, git mv followed by
git-annex sync results in the basis branch being updated to contain the
file with the new name, unlocked. This seems different than what
happens in an adjusted unlocked branch, where the commit propigates back
locked. Probably the reverse adjustment code needs to be improved to
handle this case.

Types/AdjustedBranch.hs

@@ -1,6 +1,6 @@
 {- adjusted branch types
  -
- - Copyright 2016-2018 Joey Hess <id@joeyh.name>
+ - Copyright 2016-2020 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -10,9 +10,9 @@ module Types.AdjustedBranch where
 data Adjustment
 	= LinkAdjustment LinkAdjustment
 	| PresenceAdjustment PresenceAdjustment (Maybe LinkAdjustment)
+	| LinkMissingAdjustment LinkMissingAdjustment
 	deriving (Show, Eq)
 
--- Doesn't make sense to combine unlock with fix.
 data LinkAdjustment
 	= UnlockAdjustment
 	| LockAdjustment
@@ -25,6 +25,11 @@ data PresenceAdjustment
 	| ShowMissingAdjustment
 	deriving (Show, Eq)
 
+data LinkMissingAdjustment
+	= LockMissingAdjustment
+	| UnlockMissingAdjustment
+	deriving (Show, Eq)
+
 -- Adjustments have to be able to be reversed, so that commits made to the
 -- adjusted branch can be reversed to the commit that would have been made
 -- without the adjustment and applied to the original branch.
@@ -36,6 +41,8 @@ instance ReversableAdjustment Adjustment where
 		LinkAdjustment (reverseAdjustment l)
 	reverseAdjustment (PresenceAdjustment p ml) =
 		PresenceAdjustment (reverseAdjustment p) (fmap reverseAdjustment ml)
+	reverseAdjustment (LinkMissingAdjustment l) =
+		LinkMissingAdjustment (reverseAdjustment l)
 
 instance ReversableAdjustment LinkAdjustment where
 	reverseAdjustment UnlockAdjustment = LockAdjustment
@@ -48,6 +55,10 @@ instance ReversableAdjustment PresenceAdjustment where
 	reverseAdjustment HideMissingAdjustment = ShowMissingAdjustment
 	reverseAdjustment ShowMissingAdjustment = HideMissingAdjustment
 
+instance ReversableAdjustment LinkMissingAdjustment where
+	reverseAdjustment LockMissingAdjustment = UnlockMissingAdjustment
+	reverseAdjustment UnlockMissingAdjustment = LockMissingAdjustment
+
 adjustmentHidesFiles :: Adjustment -> Bool
 adjustmentHidesFiles (PresenceAdjustment HideMissingAdjustment _) = True
 adjustmentHidesFiles _ = False