whereused --historical

Does not check the reflog, but otherwise works.

It's possible for it to display something that is not an annexed file,
if a non-annexed file somehow ends up containing something that looks
like the key's name. This seems very unlikely to happen, and it would
add a lot of complexity to detect it and somehow skip over that file,
since the git log would need to either be run again, or not limited to 1
result and canceled once enough results have been read.

Also, it kind of seems ok, if a file refers to a key, to consider that
as a place the key was used, for some definition of used. So, I punted
on dealing with that. May revisit later.

Sponsored-by: Brock Spratlen on Patreon

Command/WhereUsed.hs

@@ -8,10 +8,21 @@
 module Command.WhereUsed where
 
 import Command
+import Git
+import Git.Sha
 import Git.FilePath
+import qualified Git.Ref
+import qualified Git.Command
+import qualified Git.DiffTree as DiffTree
+import qualified Annex
+import qualified Annex.Branch
 import Annex.CatFile
 import Database.Keys
 
+import Data.Char
+import qualified Data.ByteString as S
+import qualified Data.ByteString.Lazy as L
+
 cmd :: Command
 cmd = noCommit $ withGlobalOptions [annexedMatchingOptions] $
 	command "whereused" SectionQuery
@@ -60,9 +71,62 @@ start o (_, key, _) = startingCustomOutput key $ do
 		Just k | k == key -> return True
 		_ -> return False
 
-display :: Key -> FilePath -> IO ()
+display :: Key -> String -> IO ()
-display key f = putStrLn (serializeKey key ++ " " ++ f)
+display key loc = putStrLn (serializeKey key ++ " " ++ loc)
 
 findHistorical :: Key -> Annex ()
 findHistorical key = do
-	error "TODO"
+	Annex.inRepo $ \repo -> do
+		-- Find most recent change to the key, in all branches and
+		-- tags, except the git-annex branch.
+		(output, cleanup) <- Git.Command.pipeNullSplit 
+			[ Param "log"
+			, Param "-z"
+			-- Don't convert pointer files.
+			, Param "--no-textconv"
+			-- Only find the most recent commit, for speed.
+			, Param "-n1"
+			-- Find commits that contain the key.
+			, Param ("-S" ++ fromRawFilePath (keyFile key))
+			-- Skip commits where the file was deleted,
+			-- only find those where it was added or modified.
+			, Param "--diff-filter=ACMRTUX"
+			-- Search all local branches, except git-annex branch.
+			, Param ("--exclude=*/" ++ fromRef (Annex.Branch.name))
+			, Param "--glob=*"
+			-- Also search remote branches
+			, Param ("--exclude=" ++ fromRef (Annex.Branch.name))
+			, Param "--remotes=*"
+			-- And search tags.
+			, Param "--tags=*"
+			-- Output the commit hash
+			, Param "--pretty=%H"
+			-- And the raw diff.
+			, Param "--raw"
+			-- Don't abbreviate hashes.
+			, Param "--no-abbrev"
+			] repo
+		found <- case output of
+			(h:rest) -> do
+				commitsha <- getSha "log" (pure (L.toStrict h))
+				let diff = DiffTree.parseDiffRaw rest
+				forM_ (map (flip fromTopFilePath repo . DiffTree.file) diff) $ \f -> do
+					commitdesc <- S.takeWhile (/= fromIntegral (ord '\n'))
+						<$> Git.Command.pipeReadStrict
+							[ Param "describe"
+							, Param "--contains"
+							, Param "--all"
+							, Param (fromRef commitsha)
+							] repo
+					if S.null commitdesc
+						then return False
+						else do
+							rf <- relPathCwdToFile f
+							let fref = Git.Ref.branchFileRef (Ref commitdesc) rf
+							display key (fromRef fref)
+							return True
+			_ -> return False
+		void cleanup
+		
+		unless found $ do
+			error "todo reflog"

Git/DiffTree.hs

@@ -15,6 +15,7 @@ module Git.DiffTree (
 	diffFiles,
 	diffLog,
 	commitDiff,
+	parseDiffRaw,
 ) where
 
 import qualified Data.ByteString as B
@@ -116,9 +117,13 @@ parseDiffRaw l = go l
 	go (s:[]) = error $ "diff-tree parse error near \"" ++ decodeBL' s ++ "\""
 
 -- :<srcmode> SP <dstmode> SP <srcsha> SP <dstsha> SP <status>
+--
+-- May be prefixed with a newline, which git log --pretty=format
+-- adds to the first line of the diff, even with -z.
 parserDiffRaw :: RawFilePath -> A.Parser DiffTreeItem
 parserDiffRaw f = DiffTreeItem
-	<$ A8.char ':'
+	<$ A.option '\n' (A8.char '\n')
+	<* A8.char ':'
 	<*> octal
 	<* A8.char ' '
 	<*> octal