Avoid backtraces on expected failures when built with ghc 8; only use backtraces for unexpected errors.

ghc 8 added backtraces on uncaught errors. This is great, but git-annex was
using error in many places for a error message targeted at the user, in
some known problem case. A backtrace only confuses such a message, so omit it.

Notably, commands like git annex drop that failed due to eg, numcopies,
used to use error, so had a backtrace.

This commit was sponsored by Ethan Aubin.

1 files changed, 4 insertions, 4 deletions

diff --git a/Command/FromKey.hs b/Command/FromKey.hs
index 36cc1d31f..670e9e6a6 100644
--- a/Command/FromKey.hs
+++ b/Command/FromKey.hs
@@ -33,14 +33,14 @@ start force (keyname:file:[]) = do
 	let key = mkKey keyname
 	unless force $ do
 		inbackend <- inAnnex key
-		unless inbackend $ error $
+		unless inbackend $ giveup $
 			"key ("++ keyname ++") is not present in backend (use --force to override this sanity check)"
 	showStart "fromkey" file
 	next $ perform key file
 start _ [] = do
 	showStart "fromkey" "stdin"
 	next massAdd
-start _ _ = error "specify a key and a dest file"
+start _ _ = giveup "specify a key and a dest file"
 
 massAdd :: CommandPerform
 massAdd = go True =<< map (separate (== ' ')) . lines <$> liftIO getContents
@@ -51,7 +51,7 @@ massAdd = go True =<< map (separate (== ' ')) . lines <$> liftIO getContents
 		ok <- perform' key f
 		let !status' = status && ok
 		go status' rest
-	go _ _ = error "Expected pairs of key and file on stdin, but got something else."
+	go _ _ = giveup "Expected pairs of key and file on stdin, but got something else."
 
 -- From user input to a Key.
 -- User can input either a serialized key, or an url.
@@ -66,7 +66,7 @@ mkKey s = case parseURI s of
 		Backend.URL.fromUrl s Nothing
 	_ -> case file2key s of
 		Just k -> k
-		Nothing -> error $ "bad key/url " ++ s
+		Nothing -> giveup $ "bad key/url " ++ s
 
 perform :: Key -> FilePath -> CommandPerform
 perform key file = do