add cache for getNumMinCopiesAttr

Optimises balanced=groupname:lackingcopies at the expense of a tiny
slowdown to lackingcopies=number and git-annex fsck and import.

Sponsored-by: k0ld

Annex.hs

@@ -197,6 +197,7 @@ data AnnexState = AnnexState
 	, checkignorehandle :: Maybe (ResourcePool CheckIgnoreHandle)
 	, globalnumcopies :: Maybe (Maybe NumCopies)
 	, globalmincopies :: Maybe (Maybe MinCopies)
+	, nummincopiesattrcache :: Maybe (OsPath, (Maybe NumCopies, Maybe MinCopies))
 	, limit :: ExpandableMatcher Annex
 	, timelimit :: Maybe (Duration, POSIXTime)
 	, sizelimit :: Maybe (TVar Integer)
@@ -253,6 +254,7 @@ newAnnexState c r = do
 		, checkignorehandle = Nothing
 		, globalnumcopies = Nothing
 		, globalmincopies = Nothing
+		, nummincopiesattrcache = Nothing
 		, limit = BuildingMatcher []
 		, timelimit = Nothing
 		, sizelimit = Nothing

Annex/NumCopies.hs

@@ -1,6 +1,6 @@
 {- git-annex numcopies configuration and checking
  -
- - Copyright 2014-2024 Joey Hess <id@joeyh.name>
+ - Copyright 2014-2025 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -181,12 +181,18 @@ getGlobalFileNumCopies f = fromSourcesOr defaultNumCopies
 	]
 
 getNumMinCopiesAttr :: OsPath  -> Annex (Maybe NumCopies, Maybe MinCopies)
-getNumMinCopiesAttr file =
+getNumMinCopiesAttr file = Annex.getState Annex.nummincopiesattrcache >>= \case
-	checkAttrs ["annex.numcopies", "annex.mincopies"] file >>= \case
+	Just (cfile, v) | cfile == file -> return v
-		(n:m:[]) -> return
+	_ -> checkAttrs ["annex.numcopies", "annex.mincopies"] file >>= \case
+		(n:m:[]) -> do
+			let v =
 				( configuredNumCopies <$> readish n
 				, configuredMinCopies <$> readish m
 				)
+			Annex.changeState $ \s -> s 
+				{ Annex.nummincopiesattrcache = Just (file, v)
+				}
+			return v
 		_ -> error "internal"
 
 {- Checks if numcopies are satisfied for a file by running a comparison