implement fastDebug

Most of the changes here involve global option parsing: GlobalSetter
changed so it can both run an Annex action to set state, but can also
change the AnnexRead value, which is immutable once the Annex monad is
running.

That allowed a debugselector value to be added to AnnexRead, seeded
from the git config. The --debugfilter option's GlobalSetter then updates
the AnnexRead.

This improved GlobalSetter can later be used to move more stuff to
AnnexRead. Things that don't involve a git config will be easier to
move, and probably a *lot* of things can be moved eventually.

fastDebug, while implemented, is not used anywhere yet. But it should be
fast..

CmdLine/GlobalSetter.hs

@@ -7,19 +7,30 @@
   
 module CmdLine.GlobalSetter where
 
-import Types.DeferredParse
 import Common
 import Annex
+import Types.DeferredParse
 
 import Options.Applicative
 
-globalFlag :: Annex () -> Mod FlagFields GlobalSetter -> GlobalOption
-globalFlag setter = flag' (DeferredParse setter) 
+setAnnexState :: Annex () -> GlobalSetter
+setAnnexState a = GlobalSetter a id
 
-globalSetter :: (v -> Annex ()) -> Parser v -> GlobalOption
-globalSetter setter parser = DeferredParse . setter <$> parser
+setAnnexRead :: (AnnexRead -> AnnexRead) -> GlobalSetter
+setAnnexRead f = GlobalSetter (return ()) f
 
+globalFlag :: GlobalSetter -> Mod FlagFields GlobalSetter -> GlobalOption
+globalFlag = flag'
+
+globalOption :: (v -> GlobalSetter) -> Parser v -> GlobalOption
+globalOption mk parser = mk <$> parser
+
+-- | Combines a bunch of GlobalOptions together into a Parser
+-- that returns a GlobalSetter that can be used to set all the options that
+-- are enabled.
 parserGlobalOptions :: [GlobalOption] -> Parser GlobalSetter
-parserGlobalOptions [] = DeferredParse <$> pure noop
-parserGlobalOptions l = DeferredParse . mapM_ getParsed
-	<$> many (foldl1 (<|>) l)
+parserGlobalOptions [] = pure mempty
+parserGlobalOptions l = mconcat <$> many (foldl1 (<|>) l)
+
+applyAnnexReadSetter :: GlobalSetter -> (AnnexState, AnnexRead) -> (AnnexState, AnnexRead)
+applyAnnexReadSetter gs (st, rd) = (st, annexReadSetter gs rd)