smarter BranchState cache invalidation

Only invalidate a just-written file in the cache, not the whole cache.

This will avoid the possibly performance impact of cache invalidation
mentioned in commit 770aac97a7

Annex/Branch.hs

@@ -262,7 +262,7 @@ updateTo' pairs = do
 					else commitIndex jl branchref merge_desc commitrefs
 			)
 		addMergedRefs tomerge
-		invalidateCache
+		invalidateCacheAll
 	
 	stagejournalwhen dirty jl a
 		| dirty = stageJournal jl a
@@ -487,7 +487,7 @@ set jl ru f c = do
 	-- evaluating a Journalable Builder twice, which is not very
 	-- efficient. Instead, assume that it's not common to need to read
 	-- a log file immediately after writing it.
-	invalidateCache
+	invalidateCache f
 
 {- Appends content to the journal file. -}
 append :: Journalable content => JournalLocked -> RawFilePath -> AppendableJournalFile -> content -> Annex ()
@@ -495,7 +495,7 @@ append jl f appendable toappend = do
 	journalChanged
 	appendJournalFile jl appendable toappend
 	fastDebug "Annex.Branch" ("append " ++ fromRawFilePath f)
-	invalidateCache
+	invalidateCache f
 
 {- Commit message used when making a commit of whatever data has changed
  - to the git-annex branch. -}

Annex/BranchState.hs

@@ -134,5 +134,11 @@ getCache file state = go (cachedFileContents state)
 		| f == file && not (needInteractiveAccess state) = Just c
 		| otherwise = go rest
 
-invalidateCache :: Annex ()
-invalidateCache = changeState $ \s -> s { cachedFileContents = [] }
+invalidateCache :: RawFilePath -> Annex ()
+invalidateCache f = changeState $ \s -> s
+	{ cachedFileContents = filter (\(f', _) -> f' /= f) 
+		(cachedFileContents s)
+	}
+
+invalidateCacheAll :: Annex ()
+invalidateCacheAll = changeState $ \s -> s { cachedFileContents = [] }