Write id for code block to label attr in latex when listing is used

The code:

    ~~~{#test}
    asdf
    ~~~

gets compiled to html:

    <pre id="test">
    asdf
    </pre>

So it is possible to link to the identifier `test`

But this doesn't happen on latex

When using the listings package (`--listings`) it is possible to set the
identifier using the `label=test` property:

    \begin{lstlisting}[label=id]
    hi
    \end{lstlisting}

And this is exactly what this patch is doing.

Modified LaTeX Reader/Writer and added tests for this.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/Text/Pandoc/Writers/LaTeX.hs b/src/Text/Pandoc/Writers/LaTeX.hs
index ab579a326..bf056001f 100644
--- a/src/Text/Pandoc/Writers/LaTeX.hs
+++ b/src/Text/Pandoc/Writers/LaTeX.hs
@@ -313,7 +313,7 @@ blockToLaTeX (BlockQuote lst) = do
        _ -> do
          contents <- blockListToLaTeX lst
          return $ "\\begin{quote}" $$ contents $$ "\\end{quote}"
-blockToLaTeX (CodeBlock (_,classes,keyvalAttr) str) = do
+blockToLaTeX (CodeBlock (identifier,classes,keyvalAttr) str) = do
   opts <- gets stOptions
   case () of
      _ | isEnabled Ext_literate_haskell opts && "haskell" `elem` classes &&
@@ -344,7 +344,11 @@ blockToLaTeX (CodeBlock (_,classes,keyvalAttr) str) = do
                              [ (if key == "startFrom"
                                    then "firstnumber"
                                    else key) ++ "=" ++ attr |
-                                   (key,attr) <- keyvalAttr ]
+                                   (key,attr) <- keyvalAttr ] ++
+                             (if identifier == ""
+                                   then []
+                                   else [ "label=" ++ identifier ])
+
                         else []
                printParams
                    | null params = empty