make programPath return FilePath not Maybe FilePath

Looking at the few current callers, it's ok to have programPath throw an
exception, in the unusual case where it cannot find git-annex.

3 files changed, 11 insertions, 8 deletions

diff --git a/Annex/Path.hs b/Annex/Path.hs
index 6186a887b..ac4e77645 100644
--- a/Annex/Path.hs
+++ b/Annex/Path.hs
@@ -17,9 +17,10 @@ import System.Environment
  - 
  - getExecutablePath is available since ghc 7.4.2. On OSs it supports
  - well, it returns the complete path to the program. But, on other OSs,
- - it might return just the basename.
+ - it might return just the basename. Fall back to reading the programFile,
+ - or searching for the command name in PATH.
  -}
-programPath :: IO (Maybe FilePath)
+programPath :: IO FilePath
 programPath = do
 #if MIN_VERSION_base(4,6,0)
 	exe <- getExecutablePath
@@ -29,6 +30,4 @@ programPath = do
 #else
 	p <- readProgramFile
 #endif
-	-- In case readProgramFile returned just the command name,
-	-- fall back to finding it in PATH.
-	searchPath p
+	maybe cannotFindProgram return =<< searchPath p
diff --git a/Assistant/Threads/UpgradeWatcher.hs b/Assistant/Threads/UpgradeWatcher.hs
index e779c8e54..952db1f13 100644
--- a/Assistant/Threads/UpgradeWatcher.hs
+++ b/Assistant/Threads/UpgradeWatcher.hs
@@ -36,8 +36,7 @@ upgradeWatcherThread urlrenderer = namedThread "UpgradeWatcher" $ do
 		showSuccessfulUpgrade urlrenderer
 	go =<< liftIO upgradeFlagFile
   where
-	go Nothing = debug [ "cannot determine program path" ]
-	go (Just flagfile) = do
+	go flagfile = do
 		mvar <- liftIO $ newMVar InStartupScan
 		changed <- Just <$> asIO2 (changedFile urlrenderer mvar flagfile)
 		let hooks = mkWatchHooks
diff --git a/Config/Files.hs b/Config/Files.hs
index b503a5443..d2b2f6a51 100644
--- a/Config/Files.hs
+++ b/Config/Files.hs
@@ -62,8 +62,13 @@ readProgramFile = do
 		( return p
 		, ifM (inPath cmd)
 			( return cmd
-			, error $ "cannot find git-annex program in PATH or in the location listed in " ++ programfile
+			, cannotFindProgram
 			)
 		)
   where
 	cmd = "git-annex"
+
+cannotFindProgram :: IO a
+cannotFindProgram = do
+	f <- programFile
+	error $ "cannot find git-annex program in PATH or in the location listed in " ++ f