mincopies

This is conceptually very simple, just making a 1 that was hard coded be
exposed as a config option. The hard part was plumbing all that, and
dealing with complexities like reading it from git attributes at the
same time that numcopies is read.

Behavior change: When numcopies is set to 0, git-annex used to drop
content without requiring any copies. Now to get that (highly unsafe)
behavior, mincopies also needs to be set to 0. It seemed better to
remove that edge case, than complicate mincopies by ignoring it when
numcopies is 0.

This commit was sponsored by Denis Dzyubenko on Patreon.

Git/CheckAttr.hs

@@ -1,6 +1,6 @@
 {- git check-attr interface
  -
- - Copyright 2010-2020 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2021 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -20,8 +20,8 @@ type CheckAttrHandle = (CoProcess.CoProcessHandle, [Attr], RawFilePath)
 
 type Attr = String
 
-{- Starts git check-attr running to look up the specified gitattributes
- - values and returns a handle.  -}
+{- Starts git check-attr running to look up the specified attributes
+ - and returns a handle.  -}
 checkAttrStart :: [Attr] -> Repo -> IO CheckAttrHandle
 checkAttrStart attrs repo = do
 	currdir <- R.getCurrentDirectory
@@ -38,17 +38,24 @@ checkAttrStart attrs repo = do
 checkAttrStop :: CheckAttrHandle -> IO ()
 checkAttrStop (h, _, _) = CoProcess.stop h
 
-{- Gets an attribute of a file. When the attribute is not specified,
- - returns "" -}
 checkAttr :: CheckAttrHandle -> Attr -> RawFilePath -> IO String
-checkAttr (h, attrs, currdir) want file = do
-	pairs <- CoProcess.query h send (receive "")
-	let vals = map snd $ filter (\(attr, _) -> attr == want) pairs
-	case vals of
-		["unspecified"] -> return ""
-		[v] -> return v
-		_ -> error $ "unable to determine " ++ want ++ " attribute of " ++ fromRawFilePath file
+checkAttr h want file = checkAttrs h [want] file >>= return . \case
+	(v:_) -> v
+	[] -> ""
+
+{- Gets attributes of a file. When an attribute is not specified,
+ - returns "" for it. -}
+checkAttrs :: CheckAttrHandle -> [Attr] -> RawFilePath -> IO [String]
+checkAttrs (h, attrs, currdir) want file = do
+	l <- CoProcess.query h send (receive "")
+	return (getvals l want)
   where
+	getvals _ [] = []
+	getvals l (x:xs) = case map snd $ filter (\(attr, _) -> attr == x) l of
+			["unspecified"] -> "" : getvals l xs
+			[v] -> v : getvals l xs
+			_ -> error $ "unable to determine " ++ x ++ " attribute of " ++ fromRawFilePath file
+
 	send to = B.hPutStr to $ file' `B.snoc` 0
 	receive c from = do
 		s <- hGetSomeString from 1024