LaTeX reader: tighten up reading of beamer overlay specifications.

Ideally we'd turn these on only when reading beamer, but currently
beamer is not distinguished from latex as an input format.

This commit also activates parsing of overlay specifications
after commands in general (e.g. `\item`), since they can occur
in many contexts in beamer.

Closes #4669.

1 files changed, 20 insertions, 9 deletions

diff --git a/src/Text/Pandoc/Readers/LaTeX.hs b/src/Text/Pandoc/Readers/LaTeX.hs
index 35c85d023..2fdb3d43c 100644
--- a/src/Text/Pandoc/Readers/LaTeX.hs
+++ b/src/Text/Pandoc/Readers/LaTeX.hs
@@ -1204,16 +1204,28 @@ rawopt = do
   return $ "[" <> inner <> "]"
 
 skipopts :: PandocMonad m => LP m ()
-skipopts = skipMany rawopt
+skipopts = skipMany (overlaySpecification <|> void rawopt)
 
 -- opts in angle brackets are used in beamer
-rawangle :: PandocMonad m => LP m ()
-rawangle = try $ do
+overlaySpecification :: PandocMonad m => LP m ()
+overlaySpecification = try $ do
   symbol '<'
-  () <$ manyTill anyTok (symbol '>')
-
-skipangles :: PandocMonad m => LP m ()
-skipangles = skipMany rawangle
+  ts <- manyTill overlayTok (symbol '>')
+  guard $ case ts of
+               -- see issue #3368
+               [Tok _ Word s] | T.all isLetter s -> s `elem`
+                                ["beamer","presentation", "trans",
+                                 "handout","article", "second"]
+               _ -> True
+
+overlayTok :: PandocMonad m => LP m Tok
+overlayTok =
+  satisfyTok (\t ->
+                  case t of
+                    Tok _ Word _       -> True
+                    Tok _ Spaces _     -> True
+                    Tok _ Symbol c     -> c `elem` ["-","+","@","|",":",","]
+                    _                  -> False)
 
 ignore :: (Monoid a, PandocMonad m) => String -> ParserT s u m a
 ignore raw = do
@@ -1289,7 +1301,7 @@ inlineCommands = M.union inlineLanguageCommands $ M.fromList
   , ("textup", extractSpaces (spanWith ("",["upright"],[])) <$> tok)
   , ("texttt", ttfamily)
   , ("sout", extractSpaces strikeout <$> tok)
-  , ("alert", skipangles >> spanWith ("",["alert"],[]) <$> tok) -- beamer
+  , ("alert", skipopts >> spanWith ("",["alert"],[]) <$> tok) -- beamer
   , ("lq", return (str "‘"))
   , ("rq", return (str "’"))
   , ("textquoteleft", return (str "‘"))
@@ -1765,7 +1777,6 @@ getRawCommand name txt = do
            "def" ->
              void $ manyTill anyTok braced
            _ -> do
-             skipangles
              skipopts
              option "" (try (optional sp *> dimenarg))
              void $ many braced