pushed checkPresent exception handling out of Remote implementations

I tend to prefer moving toward explicit exception handling, not away from
it, but in this case, I think there are good reasons to let checkPresent
throw exceptions:

1. They can all be caught in one place (Remote.hasKey), and we know
   every possible exception is caught there now, which we didn't before.
2. It simplified the code of the Remotes. I think it makes sense for
   Remotes to be able to be implemented without needing to worry about
   catching exceptions inside them. (Mostly.)
3. Types.StoreRetrieve.Preparer can only work on things that return a
   Bool, which all the other relevant remote methods already did.
   I do not see a good way to generalize that type; my previous attempts
   failed miserably.

2 files changed, 13 insertions, 5 deletions

diff --git a/Types/Remote.hs b/Types/Remote.hs
index 805b98474..b657cfcdc 100644
--- a/Types/Remote.hs
+++ b/Types/Remote.hs
@@ -68,12 +68,12 @@ data RemoteA a = Remote {
 	retrieveKeyFileCheap :: Key -> FilePath -> a Bool,
 	-- removes a key's contents (succeeds if the contents are not present)
 	removeKey :: Key -> a Bool,
-	-- Checks if a key is present in the remote; if the remote
-	-- cannot be accessed returns a Left error message.
-	hasKey :: Key -> a (Either String Bool),
-	-- Some remotes can check hasKey without an expensive network
+	-- Checks if a key is present in the remote.
+	-- Throws an exception if the remote cannot be accessed.
+	checkPresent :: Key -> a Bool,
+	-- Some remotes can checkPresent without an expensive network
 	-- operation.
-	hasKeyCheap :: Bool,
+	checkPresentCheap :: Bool,
 	-- Some remotes can provide additional details for whereis.
 	whereisKey :: Maybe (Key -> a [String]),
 	-- Some remotes can run a fsck operation on the remote,
diff --git a/Types/StoreRetrieve.hs b/Types/StoreRetrieve.hs
index 9fc0634c4..a21fa7866 100644
--- a/Types/StoreRetrieve.hs
+++ b/Types/StoreRetrieve.hs
@@ -33,3 +33,11 @@ type Storer = Key -> ContentSource -> MeterUpdate -> Annex Bool
 -- callback, which will fully consume the content before returning.
 -- Throws exception if key is not present, or remote is not accessible.
 type Retriever = Key -> MeterUpdate -> (ContentSource -> Annex Bool) -> Annex Bool
+
+-- Action that removes a Key's content from a remote.
+-- Succeeds if key is already not present; never throws exceptions.
+type Remover = Key -> Annex Bool
+
+-- Checks if a Key's content is present on a remote.
+-- Throws an exception if the remote is not accessible.
+type CheckPresent = Key -> Annex Bool