RST writer: Fixes bug with links with duplicate text.

We now (a) use anonymous links for links with inline URLs, and
(b) use an inline link instead of a reference link if the
reference link would require a label that has already been
used for a different link.

Closes #511.

2 files changed, 38 insertions, 34 deletions

diff --git a/src/Text/Pandoc/Writers/RST.hs b/src/Text/Pandoc/Writers/RST.hs
index 2ec2ef127..f3815011f 100644
--- a/src/Text/Pandoc/Writers/RST.hs
+++ b/src/Text/Pandoc/Writers/RST.hs
@@ -367,12 +367,16 @@ inlineToRST (Link txt (src, tit)) = do
   linktext <- inlineListToRST $ normalizeSpaces txt
   if useReferenceLinks
     then do refs <- get >>= return . stLinks
-            let refs' = if (txt, (src, tit)) `elem` refs
-                           then refs
-                           else (txt, (src, tit)):refs
-            modify $ \st -> st { stLinks = refs' }
-            return $ "`" <> linktext <> "`_"
-    else return $ "`" <> linktext <> " <" <> text src <> ">`_"
+            case lookup txt refs of
+                 Just (src',tit') ->
+                   if src == src' && tit == tit'
+                      then return $ "`" <> linktext <> "`_"
+                      else do -- duplicate label, use non-reference link
+                        return $ "`" <> linktext <> " <" <> text src <> ">`__"
+                 Nothing -> do
+                   modify $ \st -> st { stLinks = (txt,(src,tit)):refs }
+                   return $ "`" <> linktext <> "`_"
+    else return $ "`" <> linktext <> " <" <> text src <> ">`__"
 inlineToRST (Image alternate (source, tit)) = do
   label <- registerImage alternate (source,tit) Nothing
   return $ "|" <> label <> "|"
diff --git a/tests/writer.rst b/tests/writer.rst
index 399600ac0..41da5bc73 100644
--- a/tests/writer.rst
+++ b/tests/writer.rst
@@ -18,8 +18,8 @@ markdown test suite.
 Headers
 =======
 
-Level 2 with an `embedded link </url>`_
----------------------------------------
+Level 2 with an `embedded link </url>`__
+----------------------------------------
 
 Level 3 with *emphasis*
 ~~~~~~~~~~~~~~~~~~~~~~~
@@ -549,7 +549,7 @@ This is *emphasized*, and so *is this*.
 
 This is **strong**, and so **is this**.
 
-An *`emphasized link </url>`_*.
+An *`emphasized link </url>`__*.
 
 ***This is strong and em.***
 
@@ -584,7 +584,7 @@ Smart quotes, ellipses, dashes
 ‘He said, “I want to go.”’ Were you alive in the 70’s?
 
 Here is some quoted ‘``code``’ and a “`quoted
-link <http://example.com/?foo=1&bar=2>`_”.
+link <http://example.com/?foo=1&bar=2>`__”.
 
 Some dashes: one—two — three—four — five.
 
@@ -690,42 +690,42 @@ Links
 Explicit
 --------
 
-Just a `URL </url/>`_.
+Just a `URL </url/>`__.
 
-`URL and title </url/>`_.
+`URL and title </url/>`__.
 
-`URL and title </url/>`_.
+`URL and title </url/>`__.
 
-`URL and title </url/>`_.
+`URL and title </url/>`__.
 
-`URL and title </url/>`_
+`URL and title </url/>`__
 
-`URL and title </url/>`_
+`URL and title </url/>`__
 
-`with\_underscore </url/with_underscore>`_
+`with\_underscore </url/with_underscore>`__
 
-`Email link <mailto:nobody@nowhere.net>`_
+`Email link <mailto:nobody@nowhere.net>`__
 
-`Empty <>`_.
+`Empty <>`__.
 
 Reference
 ---------
 
-Foo `bar </url/>`_.
+Foo `bar </url/>`__.
 
-Foo `bar </url/>`_.
+Foo `bar </url/>`__.
 
-Foo `bar </url/>`_.
+Foo `bar </url/>`__.
 
-With `embedded [brackets] </url/>`_.
+With `embedded [brackets] </url/>`__.
 
-`b </url/>`_ by itself should be a link.
+`b </url/>`__ by itself should be a link.
 
-Indented `once </url>`_.
+Indented `once </url>`__.
 
-Indented `twice </url>`_.
+Indented `twice </url>`__.
 
-Indented `thrice </url>`_.
+Indented `thrice </url>`__.
 
 This should [not][] be a link.
 
@@ -733,21 +733,21 @@ This should [not][] be a link.
 
     [not]: /url
 
-Foo `bar </url/>`_.
+Foo `bar </url/>`__.
 
-Foo `biz </url/>`_.
+Foo `biz </url/>`__.
 
 With ampersands
 ---------------
 
 Here’s a `link with an ampersand in the
-URL <http://example.com/?foo=1&bar=2>`_.
+URL <http://example.com/?foo=1&bar=2>`__.
 
-Here’s a link with an amersand in the link text: `AT&T <http://att.com/>`_.
+Here’s a link with an amersand in the link text: `AT&T <http://att.com/>`__.
 
-Here’s an `inline link </script?foo=1&bar=2>`_.
+Here’s an `inline link </script?foo=1&bar=2>`__.
 
-Here’s an `inline link in pointy braces </script?foo=1&bar=2>`_.
+Here’s an `inline link in pointy braces </script?foo=1&bar=2>`__.
 
 Autolinks
 ---------
@@ -815,7 +815,7 @@ This paragraph should not be part of the note, as it is not indented.
 
 .. [3]
    This is *easier* to type. Inline notes may contain
-   `links <http://google.com>`_ and ``]`` verbatim characters, as well as
+   `links <http://google.com>`__ and ``]`` verbatim characters, as well as
    [bracketed text].
 
 .. [4]