Fixed RST links with no explicit link text.

The link

    `<foo>`_

should have `foo` as both its link text and its URL.

See RST spec at
<http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#embedded-uris-and-aliases>

"The reference text may also be omitted, in which case the URI will be
duplicated for use as the reference text. This is useful for relative
URIs where the address or file name is also the desired reference text:

See `<a_named_relative_link>`_ or `<an_anonymous_relative_link>`__
for details."

Closes Debian #828167 -- reported by Christian Heller.

src/Text/Pandoc/Readers/RST.hs

@@ -1126,7 +1126,10 @@ explicitLink = try $ do
   skipSpaces
   string "`_"
   optional $ char '_' -- anonymous form
-  return $ B.link (escapeURI $ trim src) "" label'
+  let label'' = if label' == mempty
+                   then B.str src
+                   else label'
+  return $ B.link (escapeURI $ trim src) "" label''
 
 referenceLink :: RSTParser Inlines
 referenceLink = try $ do

tests/rst-reader.native

@@ -211,6 +211,7 @@ Pandoc (Meta {unMeta = fromList [("author",MetaList [MetaInlines [Str "John",Spa
 ,Para [Str "Minus:",Space,Str "-"]
 ,Header 1 ("links",[],[]) [Str "Links"]
 ,Para [Str "Explicit:",Space,Str "a",Space,Link ("",[],[]) [Str "URL"] ("/url/",""),Str "."]
+,Para [Str "Explicit",Space,Str "with",Space,Str "no",Space,Str "label:",Space,Link ("",[],[]) [Str "foo"] ("foo",""),Str "."]
 ,Para [Str "Two",Space,Str "anonymous",Space,Str "links:",Space,Link ("",[],[]) [Str "the",Space,Str "first"] ("/url1/",""),Space,Str "and",Space,Link ("",[],[]) [Str "the",Space,Str "second"] ("/url2/","")]
 ,Para [Str "Reference",Space,Str "links:",Space,Link ("",[],[]) [Str "link1"] ("/url1/",""),Space,Str "and",Space,Link ("",[],[]) [Str "link2"] ("/url2/",""),Space,Str "and",Space,Link ("",[],[]) [Str "link1"] ("/url1/",""),Space,Str "again."]
 ,Para [Str "Here\8217s",Space,Str "a",Space,Link ("",[],[]) [Str "link",Space,Str "with",Space,Str "an",Space,Str "ampersand",Space,Str "in",Space,Str "the",Space,Str "URL"] ("http://example.com/?foo=1&bar=2",""),Str "."]

tests/rst-reader.rst

@@ -378,6 +378,8 @@ Links
 
 Explicit:  a `URL </url/>`_.
 
+Explicit with no label:  `<foo>`_.
+
 Two anonymous links:  `the first`__ and `the second`__
 
 __ /url1/