move/copy: option parsing for --from with --to

Allowing --from and --to as an alternative to --from or --to
is hard to do with optparse-applicative!

The obvious approach of (pfrom <|> pto <|> pfromandto) does not work
when pfromandto uses the same option names as pfrom and pto do.
It compiles but the generated parser does not work for all desired
combinations.

Instead, have to parse optionally from and optionally to. When neither
is provided, the parser succeeds, but it's a result that can't be
handled. So, have to giveup after option parsing. There does not seem to
be a way to make an optparse-applicative Parser give up internally
either.

Also, need seek' because I first tried making fto be a where binding,
but that resulted in a hang when git-annex move was run without --from
or --to. I think because startConcurrency was not expecting the stages
value to contain an exception and so ended up blocking.

Sponsored-by: Dartmouth College's DANDI project

Command/Copy.hs

@@ -1,6 +1,6 @@
 {- git-annex command
  -
- - Copyright 2010 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2023 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -21,7 +21,7 @@ cmd = withAnnexOptions [jobsOption, jsonOptions, jsonProgressOption, annexedMatc
 
 data CopyOptions = CopyOptions
 	{ copyFiles :: CmdParams
-	, fromToOptions :: FromToHereOptions
+	, fromToOptions :: Maybe FromToHereOptions
 	, keyOptions :: Maybe KeyOptions
 	, autoMode :: Bool
 	, batchOption :: BatchMode
@@ -38,13 +38,19 @@ optParser desc = CopyOptions
 instance DeferredParseClass CopyOptions where
 	finishParse v = CopyOptions
 		<$> pure (copyFiles v)
-		<*> finishParse (fromToOptions v)
+		<*> maybe (pure Nothing) (Just <$$> finishParse)
+			(fromToOptions v)
 		<*> pure (keyOptions v)
 		<*> pure (autoMode v)
 		<*> pure (batchOption v)
 
 seek :: CopyOptions -> CommandSeek
-seek o = startConcurrency commandStages $ do
+seek o = case fromToOptions o of
+	Just fto -> seek' o fto
+	Nothing -> giveup "Specify --from or --to"
+
+seek' :: CopyOptions -> FromToHereOptions -> CommandSeek
+seek' o fto = startConcurrency commandStages $ do
 	case batchOption o of
 		NoBatch -> withKeyOptions
 			(keyOptions o) (autoMode o) seeker
@@ -57,30 +63,33 @@ seek o = startConcurrency commandStages $ do
 	ww = WarnUnmatchLsFiles
 	
 	seeker = AnnexedFileSeeker
-		{ startAction = start o
-		, checkContentPresent = case fromToOptions o of
-			Right (FromRemote _) -> Just False
-			Right (ToRemote _) -> Just True
-			Left ToHere -> Just False
+		{ startAction = start o fto
+		, checkContentPresent = case fto of
+			FromOrToRemote (FromRemote _) -> Just False
+			FromOrToRemote (ToRemote _) -> Just True
+			ToHere -> Just False
+			FromRemoteToRemote _ _ -> Just False
 		, usesLocationLog = True
 		}
-	keyaction = Command.Move.startKey (fromToOptions o) Command.Move.RemoveNever
+	keyaction = Command.Move.startKey fto Command.Move.RemoveNever
 
 {- A copy is just a move that does not delete the source file.
  - However, auto mode avoids unnecessary copies, and avoids getting or
  - sending non-preferred content. -}
-start :: CopyOptions -> SeekInput -> RawFilePath -> Key -> CommandStart
-start o si file key = stopUnless shouldCopy $ 
-	Command.Move.start (fromToOptions o) Command.Move.RemoveNever si file key
+start :: CopyOptions -> FromToHereOptions -> SeekInput -> RawFilePath -> Key -> CommandStart
+start o fto si file key = stopUnless shouldCopy $ 
+	Command.Move.start fto Command.Move.RemoveNever si file key
   where
 	shouldCopy
 		| autoMode o = want <||> numCopiesCheck file key (<)
 		| otherwise = return True
-	want = case fromToOptions o of
-		Right (ToRemote dest) ->
+	want = case fto of
+		FromOrToRemote (ToRemote dest) ->
+			(Remote.uuid <$> getParsed dest) >>= checkwantsend
+		FromOrToRemote (FromRemote _) -> checkwantget
+		ToHere -> checkwantget
+		FromRemoteToRemote _ dest ->
 			(Remote.uuid <$> getParsed dest) >>= checkwantsend
-		Right (FromRemote _) -> checkwantget
-		Left ToHere -> checkwantget
 			
 	checkwantsend = wantGetBy False (Just key) (AssociatedFile (Just file))
 	checkwantget = wantGet False (Just key) (AssociatedFile (Just file))