From 5a71632d11f86cb6ed700fe3a4d717a56bad1b9e Mon Sep 17 00:00:00 2001
From: Herwig Stuetz <herwig@herwigstuetz.com>
Date: Tue, 23 May 2017 23:21:51 +0200
Subject: Parsing: `many1Till`: Check for the end condition before parsing

By not checking for the end condition before the first parse, the
parser was applied too often, consuming too much of the input.

This fixes the behaviour of

  `testStringWith (many1Till (oneOf "ab") (string "aa")) "aaa"`

which before incorrectly returned `Right "a"`. With this change, it
instead correctly fails with `Left (PandocParsecError ...)` because it
is not able to parse at least one occurence of `oneOf "ab"` that is
not `"aa"`.

Note that this only affects `many1Till p end` where `p` matches on a
prefix of `end`.
---
 src/Text/Pandoc/Parsing.hs             | 5 +++--
 src/Text/Pandoc/Readers/Org/Inlines.hs | 4 ++--
 src/Text/Pandoc/Readers/TWiki.hs       | 4 ++--
 src/Text/Pandoc/Readers/Textile.hs     | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)

(limited to 'src')

diff --git a/src/Text/Pandoc/Parsing.hs b/src/Text/Pandoc/Parsing.hs
index 225796272..cd51bff69 100644
--- a/src/Text/Pandoc/Parsing.hs
+++ b/src/Text/Pandoc/Parsing.hs
@@ -274,11 +274,12 @@ indentWith num = do
                  , try (char '\t' >> indentWith (num - tabStop)) ]
 
 -- | Like @manyTill@, but reads at least one item.
-many1Till :: Stream s m t
+many1Till :: (Show end, Stream s m t)
           => ParserT s st m a
           -> ParserT s st m end
           -> ParserT s st m [a]
 many1Till p end = do
+         notFollowedBy' end
          first <- p
          rest <- manyTill p end
          return (first:rest)
@@ -343,7 +344,7 @@ blanklines :: Stream s m Char => ParserT s st m [Char]
 blanklines = many1 blankline
 
 -- | Parses material enclosed between start and end parsers.
-enclosed :: Stream s  m Char => ParserT s st m t   -- ^ start parser
+enclosed :: (Show end, Stream s  m Char) => ParserT s st m t   -- ^ start parser
          -> ParserT s st m end  -- ^ end parser
          -> ParserT s st m a    -- ^ content parser (to be used repeatedly)
          -> ParserT s st m [a]
diff --git a/src/Text/Pandoc/Readers/Org/Inlines.hs b/src/Text/Pandoc/Readers/Org/Inlines.hs
index aa376fe25..6946e8379 100644
--- a/src/Text/Pandoc/Readers/Org/Inlines.hs
+++ b/src/Text/Pandoc/Readers/Org/Inlines.hs
@@ -687,13 +687,13 @@ mathEnd c = try $ do
   return res
 
 
-enclosedInlines :: PandocMonad m => OrgParser m a
+enclosedInlines :: (PandocMonad m, Show b) => OrgParser m a
                 -> OrgParser m b
                 -> OrgParser m (F Inlines)
 enclosedInlines start end = try $
   trimInlinesF . mconcat <$> enclosed start end inline
 
-enclosedRaw :: PandocMonad m => OrgParser m a
+enclosedRaw :: (PandocMonad m, Show b) => OrgParser m a
             -> OrgParser m b
             -> OrgParser m String
 enclosedRaw start end = try $
diff --git a/src/Text/Pandoc/Readers/TWiki.hs b/src/Text/Pandoc/Readers/TWiki.hs
index aea55b7a9..fcb95fc35 100644
--- a/src/Text/Pandoc/Readers/TWiki.hs
+++ b/src/Text/Pandoc/Readers/TWiki.hs
@@ -349,13 +349,13 @@ linebreak = newline >> notFollowedBy newline >> (lastNewline <|> innerNewline)
   where lastNewline  = eof >> return mempty
         innerNewline = return B.space
 
-between :: (Monoid c, PandocMonad m)
+between :: (Monoid c, PandocMonad m, Show b)
         => TWParser m a -> TWParser m b -> (TWParser m b -> TWParser m c)
         -> TWParser m c
 between start end p =
   mconcat <$> try (start >> notFollowedBy whitespace >> many1Till (p end) end)
 
-enclosed :: (Monoid b, PandocMonad m)
+enclosed :: (Monoid b, PandocMonad m, Show a)
          => TWParser m a -> (TWParser m a -> TWParser m b) -> TWParser m b
 enclosed sep p = between sep (try $ sep <* endMarker) p
   where
diff --git a/src/Text/Pandoc/Readers/Textile.hs b/src/Text/Pandoc/Readers/Textile.hs
index 52f4f2493..0b964dd63 100644
--- a/src/Text/Pandoc/Readers/Textile.hs
+++ b/src/Text/Pandoc/Readers/Textile.hs
@@ -692,7 +692,7 @@ langAttr = do
   return $ \(id',classes,keyvals) -> (id',classes,("lang",lang):keyvals)
 
 -- | Parses material surrounded by a parser.
-surrounded :: PandocMonad m
+surrounded :: (PandocMonad m, Show t)
            => ParserT [Char] st m t   -- ^ surrounding parser
            -> ParserT [Char] st m a   -- ^ content parser (to be used repeatedly)
            -> ParserT [Char] st m [a]
-- 
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