Merge pull request #1989 from zudov/shortcut_ref_link_pr

Support shortcut reference links in markdown writer

5 files changed, 158 insertions, 31 deletions

diff --git a/README b/README
index 8c8e8c957..f13e378ce 100644
--- a/README
+++ b/README
@@ -2790,6 +2790,11 @@ in several respects:
     we must either disallow lazy wrapping or require a blank line between
     list items.
 
+#### Extension: `shortcut_reference_links` ####
+
+Allows to use shortcut reference links: `[foo]` instead of `[foo][]`. Writer
+would shortcut links unless doing so might cause problems.
+
 Markdown variants
 -----------------
 
diff --git a/src/Text/Pandoc/Options.hs b/src/Text/Pandoc/Options.hs
index 29989f8c5..a5dcbfd0b 100644
--- a/src/Text/Pandoc/Options.hs
+++ b/src/Text/Pandoc/Options.hs
@@ -109,6 +109,7 @@ data Extension =
     | Ext_implicit_header_references -- ^ Implicit reference links for headers
     | Ext_line_blocks         -- ^ RST style line blocks
     | Ext_epub_html_exts      -- ^ Recognise the EPUB extended version of HTML
+    | Ext_shortcut_reference_links -- ^ Shortcut reference links
     deriving (Show, Read, Enum, Eq, Ord, Bounded)
 
 pandocExtensions :: Set Extension
@@ -151,6 +152,7 @@ pandocExtensions = Set.fromList
   , Ext_header_attributes
   , Ext_implicit_header_references
   , Ext_line_blocks
+  , Ext_shortcut_reference_links
   ]
 
 phpMarkdownExtraExtensions :: Set Extension
@@ -164,6 +166,7 @@ phpMarkdownExtraExtensions = Set.fromList
   , Ext_intraword_underscores
   , Ext_header_attributes
   , Ext_abbreviations
+  , Ext_shortcut_reference_links
   ]
 
 githubMarkdownExtensions :: Set Extension
@@ -180,6 +183,7 @@ githubMarkdownExtensions = Set.fromList
   , Ext_strikeout
   , Ext_hard_line_breaks
   , Ext_lists_without_preceding_blankline
+  , Ext_shortcut_reference_links
   ]
 
 multimarkdownExtensions :: Set Extension
@@ -202,7 +206,9 @@ multimarkdownExtensions = Set.fromList
 
 strictExtensions :: Set Extension
 strictExtensions = Set.fromList
-  [ Ext_raw_html ]
+  [ Ext_raw_html
+  , Ext_shortcut_reference_links
+  ]
 
 data ReaderOptions = ReaderOptions{
          readerExtensions      :: Set Extension  -- ^ Syntax extensions
diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index fcd18fdc0..a36c2acde 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -1677,6 +1677,7 @@ referenceLink constructor (lab, raw) = do
       lookAhead (try (spnl >> normalCite >> return (mempty, "")))
       <|>
       try (spnl >> reference)
+  when (raw' == "") $ guardEnabled Ext_shortcut_reference_links
   let labIsRef = raw' == "" || raw' == "[]"
   let key = toKey $ if labIsRef then raw else raw'
   parsedRaw <- parseFromString (mconcat <$> many inline) raw'
diff --git a/src/Text/Pandoc/Writers/Markdown.hs b/src/Text/Pandoc/Writers/Markdown.hs
index 4ffdb2b36..ebf7e20e2 100644
--- a/src/Text/Pandoc/Writers/Markdown.hs
+++ b/src/Text/Pandoc/Writers/Markdown.hs
@@ -57,14 +57,15 @@ import qualified Data.Text as T
 
 type Notes = [[Block]]
 type Refs = [([Inline], Target)]
-data WriterState = WriterState { stNotes  :: Notes
-                               , stRefs   :: Refs
-                               , stInList :: Bool
-                               , stIds    :: [String]
-                               , stPlain  :: Bool }
+data WriterState = WriterState { stNotes           :: Notes
+                               , stRefs            :: Refs
+                               , stRefShortcutable :: Bool
+                               , stInList          :: Bool
+                               , stIds             :: [String]
+                               , stPlain           :: Bool }
 instance Default WriterState
-  where def = WriterState{ stNotes = [], stRefs = [], stInList = False,
-                           stIds = [], stPlain = False }
+  where def = WriterState{ stNotes = [], stRefs = [], stRefShortcutable = True,
+                           stInList = False, stIds = [], stPlain = False }
 
 -- | Convert Pandoc to Markdown.
 writeMarkdown :: WriterOptions -> Pandoc -> String
@@ -695,27 +696,47 @@ getReference label (src, tit) = do
 inlineListToMarkdown :: WriterOptions -> [Inline] -> State WriterState Doc
 inlineListToMarkdown opts lst = do
   inlist <- gets stInList
-  mapM (inlineToMarkdown opts)
-     (if inlist then avoidBadWraps lst else lst) >>= return . cat
-  where avoidBadWraps [] = []
-        avoidBadWraps (Space:Str ('>':cs):xs) =
-          Str (' ':'>':cs) : avoidBadWraps xs
-        avoidBadWraps (Space:Str [c]:[])
-          | c `elem` "-*+" = Str [' ', c] : []
-        avoidBadWraps (Space:Str [c]:Space:xs)
-          | c `elem` "-*+" = Str [' ', c] : Space : avoidBadWraps xs
-        avoidBadWraps (Space:Str cs:Space:xs)
-          | isOrderedListMarker cs = Str (' ':cs) : Space : avoidBadWraps xs
-        avoidBadWraps (Space:Str cs:[])
-          | isOrderedListMarker cs = Str (' ':cs) : []
-        avoidBadWraps (x:xs) = x : avoidBadWraps xs
-        isOrderedListMarker xs = endsWithListPunct xs &&
-                      isRight (runParserT (anyOrderedListMarker >> eof)
-                               defaultParserState "" xs)
-        endsWithListPunct xs = case reverse xs of
-                                     '.':_ -> True
-                                     ')':_ -> True
-                                     _     -> False
+  go (if inlist then avoidBadWrapsInList lst else lst)
+  where go [] = return empty
+        go (i:is) = case i of
+            (Link _ _) -> case is of
+                -- If a link is followed by another link or '[' we don't shortcut
+                (Link _ _):_                  -> unshortcutable
+                Space:(Link _ _):_            -> unshortcutable
+                Space:(Str('[':_)):_          -> unshortcutable
+                Space:(RawInline _ ('[':_)):_ -> unshortcutable
+                Space:(Cite _ _):_            -> unshortcutable
+                (Cite _ _):_                  -> unshortcutable
+                Str ('[':_):_                 -> unshortcutable
+                (RawInline _ ('[':_)):_       -> unshortcutable
+                (RawInline _ (' ':'[':_)):_   -> unshortcutable
+                _                             -> shortcutable
+            _ -> shortcutable
+          where shortcutable = liftM2 (<>) (inlineToMarkdown opts i) (go is)
+                unshortcutable = do
+                    iMark <- withState (\s -> s { stRefShortcutable = False })
+                                       (inlineToMarkdown opts i)
+                    modify (\s -> s {stRefShortcutable = True })
+                    fmap (iMark <>) (go is)
+
+avoidBadWrapsInList :: [Inline] -> [Inline]
+avoidBadWrapsInList [] = []
+avoidBadWrapsInList (Space:Str ('>':cs):xs) =
+  Str (' ':'>':cs) : avoidBadWrapsInList xs
+avoidBadWrapsInList (Space:Str [c]:[])
+  | c `elem` "-*+" = Str [' ', c] : []
+avoidBadWrapsInList (Space:Str [c]:Space:xs)
+  | c `elem` "-*+" = Str [' ', c] : Space : avoidBadWrapsInList xs
+avoidBadWrapsInList (Space:Str cs:Space:xs)
+  | isOrderedListMarker cs = Str (' ':cs) : Space : avoidBadWrapsInList xs
+avoidBadWrapsInList (Space:Str cs:[])
+  | isOrderedListMarker cs = Str (' ':cs) : []
+avoidBadWrapsInList (x:xs) = x : avoidBadWrapsInList xs
+
+isOrderedListMarker :: String -> Bool
+isOrderedListMarker xs = (last xs `elem` ".)") &&
+              isRight (runParserT (anyOrderedListMarker >> eof)
+                       defaultParserState "" xs)
 
 isRight :: Either a b -> Bool
 isRight (Right _) = True
@@ -878,6 +899,9 @@ inlineToMarkdown opts (Link txt (src, tit)) = do
                       [Str s] | escapeURI s == srcSuffix -> True
                       _                                  -> False
   let useRefLinks = writerReferenceLinks opts && not useAuto
+  shortcutable <- gets stRefShortcutable
+  let useShortcutRefLinks = shortcutable &&
+                            isEnabled Ext_shortcut_reference_links opts
   ref <- if useRefLinks then getReference txt (src, tit) else return []
   reftext <- inlineListToMarkdown opts ref
   return $ if useAuto
@@ -887,7 +911,9 @@ inlineToMarkdown opts (Link txt (src, tit)) = do
               else if useRefLinks
                       then let first  = "[" <> linktext <> "]"
                                second = if txt == ref
-                                           then "[]"
+                                           then if useShortcutRefLinks
+                                                   then ""
+                                                   else "[]"
                                            else "[" <> reftext <> "]"
                            in  first <> second
                       else if plain
diff --git a/tests/Tests/Writers/Markdown.hs b/tests/Tests/Writers/Markdown.hs
index c2a8f5903..dce40ddcb 100644
--- a/tests/Tests/Writers/Markdown.hs
+++ b/tests/Tests/Writers/Markdown.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_GHC -fno-warn-name-shadowing #-}
 module Tests.Writers.Markdown (tests) where
 
 import Test.Framework
@@ -35,4 +36,92 @@ tests = [ "indented code after list"
              =: bulletList [ plain "foo" <> bulletList [ plain "bar" ],
                              plain "baz" ]
              =?> "-   foo\n    -   bar\n-   baz\n"
-        ]
+        ] ++ [shortcutLinkRefsTests]
+
+shortcutLinkRefsTests :: Test
+shortcutLinkRefsTests =
+  let infix 4 =:
+      (=:) :: (ToString a, ToPandoc a)
+           => String -> (a, String) -> Test
+      (=:) = test (writeMarkdown (def {writerReferenceLinks = True}) . toPandoc)
+  in testGroup "Shortcut reference links"
+     [ "Simple link (shortcutable)"
+           =: (para (link "/url" "title" "foo"))
+           =?> "[foo]\n\n  [foo]: /url \"title\""
+     , "Followed by another link (unshortcutable)"
+           =: (para ((link "/url1" "title1" "first")
+                  <> (link "/url2" "title2" "second")))
+           =?> unlines [ "[first][][second]"
+                       , ""
+                       , "  [first]: /url1 \"title1\""
+                       , "  [second]: /url2 \"title2\""
+                       ]
+     , "Followed by space and another link (unshortcutable)"
+           =: (para ((link "/url1" "title1" "first") <> " "
+                  <> (link "/url2" "title2" "second")))
+           =?> unlines [ "[first][] [second]"
+                       , ""
+                       , "  [first]: /url1 \"title1\""
+                       , "  [second]: /url2 \"title2\""
+                       ]
+     , "Reference link is used multiple times (unshortcutable)"
+           =: (para ((link "/url1" "" "foo") <> (link "/url2" "" "foo")
+                                             <> (link "/url3" "" "foo")))
+           =?> unlines [ "[foo][][foo][1][foo][2]"
+                       , ""
+                       , "  [foo]: /url1"
+                       , "  [1]: /url2"
+                       , "  [2]: /url3"
+                       ]
+     , "Reference link is used multiple times (unshortcutable)"
+           =: (para ((link "/url1" "" "foo") <> " " <> (link "/url2" "" "foo")
+                                             <> " " <> (link "/url3" "" "foo")))
+           =?> unlines [ "[foo][] [foo][1] [foo][2]"
+                       , ""
+                       , "  [foo]: /url1"
+                       , "  [1]: /url2"
+                       , "  [2]: /url3"
+                       ]
+     , "Reference link is followed by text in brackets"
+          =:  (para ((link "/url" "" "link") <> "[text in brackets]"))
+          =?> unlines [ "[link][][text in brackets]"
+                      , ""
+                      , "  [link]: /url"
+                      ]
+     , "Reference link is followed by space and text in brackets"
+          =:  (para ((link "/url" "" "link") <> " [text in brackets]"))
+          =?> unlines [ "[link][] [text in brackets]"
+                      , ""
+                      , "  [link]: /url"
+                      ]
+     , "Reference link is followed by RawInline"
+          =: (para ((link "/url" "" "link") <> rawInline "markdown" "[rawText]"))
+          =?> unlines [ "[link][][rawText]"
+                      , ""
+                      , "  [link]: /url"
+                      ]
+     , "Reference link is followed by space and RawInline"
+          =: (para ((link "/url" "" "link") <> space <> rawInline "markdown" "[rawText]"))
+          =?> unlines [ "[link][] [rawText]"
+                      , ""
+                      , "  [link]: /url"
+                      ]
+     , "Reference link is followed by RawInline with space"
+          =: (para ((link "/url" "" "link") <> rawInline "markdown" " [rawText]"))
+          =?> unlines [ "[link][] [rawText]"
+                      , ""
+                      , "  [link]: /url"
+                      ]
+     , "Reference link is followed by citation"
+          =: (para ((link "/url" "" "link") <> cite [Citation "author" [] [] NormalCitation 0 0] (str "[@author]")))
+          =?> unlines [ "[link][][@author]"
+                      , ""
+                      , "  [link]: /url"
+                      ]
+     , "Reference link is followed by space and citation"
+          =: (para ((link "/url" "" "link") <> space <> cite [Citation "author" [] [] NormalCitation 0 0] (str "[@author]")))
+          =?> unlines [ "[link][] [@author]"
+                      , ""
+                      , "  [link]: /url"
+                      ]
+     ]