more command-specific options

Made --from and --to command-specific options.

Added generic storage for values of command-specific options,
which allows removing some of the special case fields in AnnexState.

(Also added generic storage for command-specific flags, although there are
not yet any.)

Note that this storage uses a Map, so repeatedly looking up the same value
is slightly more expensive than looking up an AnnexState field. But, the
value can be looked up once in the seek stage, transformed as necessary,
and passed in a closure to the start stage, and this avoids that overhead.

Still, I'm hesitant to use this for things like force or fast flags.
It's probably best to reserve it for flags that are only used by a few
commands, or options like --from and --to that it's important only be
allowed to be used with commands that implement them, to avoid user
confusion.

1 files changed, 9 insertions, 0 deletions

diff --git a/Seek.hs b/Seek.hs
index 80f31dd96..af074c7c5 100644
--- a/Seek.hs
+++ b/Seek.hs
@@ -87,6 +87,15 @@ withKeys a params = return $ map (a . parse) params
 	where
 		parse p = fromMaybe (error "bad key") $ readKey p
 
+{- Modifies a seek action using the value of a field, which is fed into
+ - a conversion function, and then is passed into the seek action.
+ - This ensures that the conversion function only runs once.
+ -}
+withField :: String -> (Maybe String -> a) -> (a -> CommandSeek) -> CommandSeek
+withField field converter a ps = do
+        f <- converter <$> Annex.getField field
+        a f ps
+
 withNothing :: CommandStart -> CommandSeek
 withNothing a [] = return [a]
 withNothing _ _ = error "This command takes no parameters."