purify exportActions

Purifying exportActions will allow introspecting and modifying it,
which is needed to add progress bar display to it.

Only S3 and WebDAV ran an Annex action while constructing ExportActions.
There was a small performance gain from them doing that, since a
resource was able to be prepared and reused for multiple actions by
Command.Export.

As seen in commit 809cfbbd8a and
5d394023eb S3 and WebDAV actually create a
new handle for each access in normal, non-export use. It doesn't seem
worth making export use of them marginally more efficient than normal
use. It would be better to do that work upfront when constructing the
remote. Or perhaps use a MVar to cache a handle.

This commit was sponsored by Nick Piper on Patreon.

Remote/Helper/Export.hs

@@ -31,8 +31,8 @@ class HasExportUnsupported a where
 instance HasExportUnsupported (RemoteConfig -> RemoteGitConfig -> Annex Bool) where
 	exportUnsupported = \_ _ -> return False
 
-instance HasExportUnsupported (Annex (ExportActions Annex)) where
-	exportUnsupported = return $ ExportActions
+instance HasExportUnsupported (ExportActions Annex) where
+	exportUnsupported = ExportActions
 		{ storeExport = \_ _ _ _ -> do
 			warning "store export is unsupported"
 			return False
@@ -182,10 +182,8 @@ adjustExportable r = case M.lookup "exporttree" (config r) of
 			-- non-export remote)
 			, checkPresent = if appendonly r
 				then checkPresent r
-				else \k -> do
-					ea <- exportActions r
-					anyM (checkPresentExport ea k)
-						=<< getexportlocs k
+				else \k -> anyM (checkPresentExport (exportActions r) k)
+					=<< getexportlocs k
 			-- checkPresent from an export is more expensive
 			-- than otherwise, so not cheap. Also, this
 			-- avoids things that look at checkPresentCheap and
@@ -211,9 +209,7 @@ adjustExportable r = case M.lookup "exporttree" (config r) of
 							, warning "unknown export location"
 							)
 						return False
-					(l:_) -> do
-						ea <- exportActions r
-						retrieveExport ea k l dest p
+					(l:_) -> retrieveExport (exportActions r) k l dest p
 			else do
 				warning $ "exported content cannot be verified due to using the " ++ decodeBS (formatKeyVariety (keyVariety k)) ++ " backend"
 				return False