LaTeX reader: Simplify decision about unknown commands...

...at the start of a paragraph, taking them to be inline
only if they're followed by regular text.  This is simpler
than our previous test (checking to see that none of
the commands on the line are inline), but it is less fragile.
(The old test broke with some changes, soon to be committed,
that change tokenization of control sequences, including trailing
newlines.)

src/Text/Pandoc/Readers/LaTeX.hs

@@ -771,33 +771,18 @@ blockCommand :: PandocMonad m => LP m Blocks
 blockCommand = try $ do
   Tok _ (CtrlSeq name) txt <- anyControlSeq
   guard $ name /= "begin" && name /= "end" && name /= "and"
+  guard $ isBlockCommand name || not (isInlineCommand name)
+  unless (isBlockCommand name) $
+    -- if it could be either inline or block, take it to be inline
+    -- if regular text follows:
+    notFollowedBy $ try $ optional whitespace >> satisfyTok isWordTok
   star <- option "" ("*" <$ symbol '*' <* sp)
   let name' = name <> star
   let names = ordNub [name', name]
-  let rawDefiniteBlock = do
-        guard $ isBlockCommand name
+  let raw = do
         rawcontents <- getRawCommand name (txt <> star)
         (guardEnabled Ext_raw_tex >> return (rawBlock "latex" rawcontents))
           <|> ignore rawcontents
-  -- heuristic:  if it could be either block or inline, we
-  -- treat it if block if we have a sequence of block
-  -- commands followed by a newline.  But we stop if we
-  -- hit a \startXXX, since this might start a raw ConTeXt
-  -- environment (this is important because this parser is
-  -- used by the Markdown reader).
-  let startCommand = try $ do
-        Tok _ (CtrlSeq n) _ <- anyControlSeq
-        guard $ "start" `T.isPrefixOf` n
-  let rawMaybeBlock = try $ do
-        guard $ not $ isInlineCommand name
-        rawcontents <- getRawCommand name (txt <> star)
-        curr <- (guardEnabled Ext_raw_tex >>
-                    return (rawBlock "latex" rawcontents))
-                   <|> ignore rawcontents
-        rest <- many $ notFollowedBy startCommand *> blockCommand
-        lookAhead $ blankline <|> startCommand
-        return $ curr <> mconcat rest
-  let raw = rawDefiniteBlock <|> rawMaybeBlock
   lookupListDefault raw names blockCommands
 
 closing :: PandocMonad m => LP m Blocks