also avoid crashing in most circumstances if unable to determine the username

Mostly the username is only used for the git committer or other display
purposes, and we can just fall back to a dummy value in these cases.

The only remaining place where an error is thrown is when starting local
pairing, which needs the username to be known.

Utility/UserInfo.hs

@@ -15,7 +15,7 @@ module Utility.UserInfo (
 ) where
 
 import Utility.Env
-import Utility.Exception
+import Utility.Data
 
 import System.PosixCompat
 import Control.Applicative
@@ -25,7 +25,7 @@ import Prelude
  -
  - getpwent will fail on LDAP or NIS, so use HOME if set. -}
 myHomeDir :: IO FilePath
-myHomeDir = myVal env homeDirectory
+myHomeDir = either error return =<< myVal env homeDirectory
   where
 #ifndef mingw32_HOST_OS
 	env = ["HOME"]
@@ -34,7 +34,7 @@ myHomeDir = myVal env homeDirectory
 #endif
 
 {- Current user's user name. -}
-myUserName :: IO String
+myUserName :: IO (Either String String)
 myUserName = myVal env userName
   where
 #ifndef mingw32_HOST_OS
@@ -48,15 +48,15 @@ myUserGecos :: IO (Maybe String)
 #if defined(__ANDROID__) || defined(mingw32_HOST_OS)
 myUserGecos = return Nothing
 #else
-myUserGecos = catchMaybeIO $ myVal [] userGecos
+myUserGecos = eitherToMaybe <$> myVal [] userGecos
 #endif
 
-myVal :: [String] -> (UserEntry -> String) -> IO String
+myVal :: [String] -> (UserEntry -> String) -> IO (Either String String)
 myVal envvars extract = go envvars
   where
 #ifndef mingw32_HOST_OS
-	go [] = extract <$> (getUserEntryForID =<< getEffectiveUserID)
+	go [] = Right . extract <$> (getUserEntryForID =<< getEffectiveUserID)
 #else
-	go [] = extract <$> error ("environment not set: " ++ show envvars)
+	go [] = return $ Left ("environment not set: " ++ show envvars)
 #endif
-	go (v:vs) = maybe (go vs) return =<< getEnv v
+	go (v:vs) = maybe (go vs) (return . Right) =<< getEnv v