Improve error message when --in @date is used and there is no reflog for the git-annex branch.

Annex/Branch.hs

@@ -38,6 +38,7 @@ import Annex.Index
 import qualified Git
 import qualified Git.Command
 import qualified Git.Ref
+import qualified Git.RefLog
 import qualified Git.Sha
 import qualified Git.Branch
 import qualified Git.UnionMerge
@@ -205,7 +206,13 @@ getRaw :: FilePath -> Annex String
 getRaw = getRef fullname
 
 getHistorical :: RefDate -> FilePath -> Annex String
-getHistorical date = getRef (Git.Ref.dateRef fullname date)
+getHistorical date file =
+	-- This check avoids some ugly error messages when the reflog
+	-- is empty.
+	ifM (null <$> inRepo (Git.RefLog.get' [Param "-n1"] fullname))
+		( error ("No reflog for " ++ fromRef fullname)
+		, getRef (Git.Ref.dateRef fullname date) file
+		)
 
 getRef :: Ref -> FilePath -> Annex String
 getRef ref file = withIndex $ decodeBS <$> catFile ref file

Git/RefLog.hs

@@ -14,9 +14,14 @@ import Git.Sha
 
 {- Gets the reflog for a given branch. -}
 get :: Branch -> Repo -> IO [Sha]
-get b = mapMaybe extractSha . lines <$$> pipeReadStrict
-	[ Param "log"
-	, Param "-g"
-	, Param "--format=%H"
-	, Param (fromRef b)
-	]
+get = get' []
+
+get' :: [CommandParam] -> Branch -> Repo -> IO [Sha]
+get' ps b = mapMaybe extractSha . lines <$$> pipeReadStrict ps'
+  where
+	ps' = 
+		[ Param "log"
+		, Param "-g"
+		, Param "--format=%H"
+		, Param (fromRef b)
+		] ++ ps

debian/changelog

@@ -12,6 +12,8 @@ git-annex (5.20150318) UNRELEASED; urgency=medium
   * --auto is no longer a global option; only get, drop, and copy
     accept it. (Not a behavior change unless you were passing it to a
     command that ignored it.)
+  * Improve error message when --in @date is used and there is no
+    reflog for the git-annex branch.
 
  -- Joey Hess <id@joeyh.name>  Thu, 19 Mar 2015 17:05:32 -0400
 

doc/bugs/Using_date_matching_options_gives_scary_error_messaes_on_empty_reflog.mdwn

@@ -31,3 +31,5 @@ git-annex: fd:9: hFlush: resource vanished (Broken pipe)
 
 # End of transcript or log.
 """]]
+
+> [[fixed|done]] --[[Joey]]