HTML reader: retain attribute prefixes and avoid duplicates.

Previously we stripped attribute prefixes, reading
`xml:lang` as `lang` for example. This resulted in
two duplicate `lang` attributes when `xml:lang` and
`lang` were both used.  This commit causes the prefixes
to be retained, and also avoids invald duplicate
attributes.

Closes #6938.

2 files changed, 24 insertions, 24 deletions

diff --git a/src/Text/Pandoc/Readers/HTML.hs b/src/Text/Pandoc/Readers/HTML.hs
index eb78979a3..f870a241d 100644
--- a/src/Text/Pandoc/Readers/HTML.hs
+++ b/src/Text/Pandoc/Readers/HTML.hs
@@ -74,7 +74,7 @@ readHtml :: PandocMonad m
          -> Text        -- ^ String to parse (assumes @'\n'@ line endings)
          -> m Pandoc
 readHtml opts inp = do
-  let tags = stripPrefixes . canonicalizeTags $
+  let tags = stripPrefixes $ canonicalizeTags $
              parseTagsOptions parseOptions{ optTagPosition = True }
              (crFilter inp)
       parseDoc = do
@@ -95,6 +95,15 @@ readHtml opts inp = do
     Right doc -> return doc
     Left  err -> throwError $ PandocParseError $ T.pack $ getError err
 
+-- Strip namespace prefixes on tags (not attributes)
+stripPrefixes :: [Tag Text] -> [Tag Text]
+stripPrefixes = map stripPrefix
+
+stripPrefix :: Tag Text -> Tag Text
+stripPrefix (TagOpen s as) = TagOpen (T.takeWhileEnd (/=':') s) as
+stripPrefix (TagClose s)   = TagClose (T.takeWhileEnd (/=':') s)
+stripPrefix x = x
+
 replaceNotes :: PandocMonad m => [Block] -> TagParser m [Block]
 replaceNotes bs = do
   st <- getState
@@ -114,7 +123,7 @@ setInPlain = local (\s -> s {inPlain = True})
 pHtml :: PandocMonad m => TagParser m Blocks
 pHtml = try $ do
   (TagOpen "html" attr) <- lookAhead pAny
-  for_ (lookup "lang" attr) $
+  for_ (lookup "lang" attr <|> lookup "xml:lang" attr) $
     updateState . B.setMeta "lang" . B.text
   pInTags "html" block
 
@@ -1024,21 +1033,6 @@ htmlTag f = try $ do
          handleTag tagname
        _ -> mzero
 
--- Strip namespace prefixes
-stripPrefixes :: [Tag Text] -> [Tag Text]
-stripPrefixes = map stripPrefix
-
-stripPrefix :: Tag Text -> Tag Text
-stripPrefix (TagOpen s as) =
-    TagOpen (stripPrefix' s) (map (first stripPrefix') as)
-stripPrefix (TagClose s) = TagClose (stripPrefix' s)
-stripPrefix x = x
-
-stripPrefix' :: Text -> Text
-stripPrefix' s =
-  if T.null t then s else T.drop 1 t
-  where (_, t) = T.span (/= ':') s
-
 -- Utilities
 
 -- | Adjusts a url according to the document's base URL.
diff --git a/src/Text/Pandoc/Readers/HTML/Parsing.hs b/src/Text/Pandoc/Readers/HTML/Parsing.hs
index 2d58319da..e28ebe77b 100644
--- a/src/Text/Pandoc/Readers/HTML/Parsing.hs
+++ b/src/Text/Pandoc/Readers/HTML/Parsing.hs
@@ -193,14 +193,20 @@ t1 `closes` t2 |
 _ `closes` _ = False
 
 toStringAttr :: [(Text, Text)] -> [(Text, Text)]
-toStringAttr = map go
+toStringAttr = foldr go []
   where
-   go (x,y) =
-     case T.stripPrefix "data-" x of
-       Just x' | x' `Set.notMember` (html5Attributes <>
-                                     html4Attributes <> rdfaAttributes)
-         -> (x',y)
-       _ -> (x,y)
+   go :: (Text, Text) -> [(Text, Text)] -> [(Text, Text)]
+   -- treat xml:lang as lang
+   go ("xml:lang",y) ats = go ("lang",y) ats
+   -- prevent duplicate attributes
+   go (x,y) ats
+     | any (\(x',_) -> x == x') ats = ats
+     | otherwise      =
+        case T.stripPrefix "data-" x of
+          Just x' | x' `Set.notMember` (html5Attributes <>
+                                        html4Attributes <> rdfaAttributes)
+            -> go (x',y) ats
+          _ -> (x,y):ats
 
 -- Unlike fromAttrib from tagsoup, this distinguishes
 -- between a missing attribute and an attribute with empty content.