metadata: Added --remove-all.

Motivation is to remove all metadata when it gets copied from a previous
version of the file, and that is not deisrable.

This commit was supported by the NSF-funded DataLad project.

CHANGELOG

@@ -2,6 +2,7 @@ git-annex (6.20170926) UNRELEASED; urgency=medium
 
   * webdav: Improve error message for failed request to include the request
     method and path.
+  * metadata: Added --remove-all.
 
  -- Joey Hess <id@joeyh.name>  Thu, 28 Sep 2017 12:01:39 -0400
 

Command/MetaData.hs

@@ -64,6 +64,10 @@ optParser desc = MetaDataOptions
 			( long "remove"  <> short 'r' <> metavar "FIELD"
 			<> help "remove all values of a field"
 			)
+		<|> flag' DelAllMeta
+			( long "remove-all"
+			<> help "remove all metadata"
+			)
 
 seek :: MetaDataOptions -> CommandSeek
 seek o = case batchOption o of

Types/MetaData.hs

@@ -244,12 +244,17 @@ removeEmptyFields (MetaData m) = MetaData $ M.filter (not . S.null) m
 metaDataValues :: MetaField -> MetaData -> S.Set MetaValue
 metaDataValues f (MetaData m) = fromMaybe S.empty (M.lookup f m)
 
+mapMetaData :: (S.Set MetaValue -> S.Set MetaValue) -> MetaData -> MetaData
+mapMetaData f (MetaData m) = MetaData (M.map f m)
+
 {- Ways that existing metadata can be modified -}
 data ModMeta
 	= AddMeta MetaField MetaValue
 	| DelMeta MetaField (Maybe MetaValue)
 	-- ^ delete value of a field. With Just, only that specific value
-	-- is deleted; with Nothing, all current values are deleted.
+	-- is deleted; with Nothing, all current values are deleted.a
+	| DelAllMeta
+	-- ^ delete all currently set metadata
 	| SetMeta MetaField (S.Set MetaValue)
 	-- ^ removes any existing values
 	| MaybeSetMeta MetaField MetaValue
@@ -265,6 +270,9 @@ modMeta _ (DelMeta f (Just oldv)) =
 	updateMetaData f (unsetMetaValue oldv) emptyMetaData
 modMeta m (DelMeta f Nothing) = MetaData $ M.singleton f $
 	S.fromList $ map unsetMetaValue $ S.toList $ currentMetaDataValues f m
+modMeta m DelAllMeta = mapMetaData
+	(S.fromList . map unsetMetaValue . S.toList)
+	(currentMetaData m)
 modMeta m (SetMeta f s) = updateMetaData' f s $
 	foldr (updateMetaData f) emptyMetaData $
 		map unsetMetaValue $ S.toList $ currentMetaDataValues f m

doc/git-annex-metadata.mdwn

@@ -60,6 +60,15 @@ automatically.
 
   Unset a tag.
 
+* `--remove-all`
+
+  Remove all metadata from the specified files.
+
+  When a file is modified and the new version added, git-annex will copy
+  over the metadata from the old version of the file. In situations where
+  you don't want that copied metadata, you can use this option to remove
+  it.
+
 * `--force`
 
   By default, `git annex metadata` refuses to recursively set metadata