LaTeX writer: only use hyperdef on section if there's a link to it.

src/Text/Pandoc/Writers/LaTeX.hs

@@ -64,6 +64,7 @@ data WriterState =
               , stHighlighting  :: Bool          -- true if document has highlighted code
               , stFirstFrame    :: Bool          -- true til we've written first beamer frame
               , stIncremental   :: Bool          -- true if beamer lists should be displayed bit by bit
+              , stInternalLinks :: [String]      -- list of internal link targets
               }
 
 -- | Convert Pandoc to LaTeX.
@@ -77,10 +78,15 @@ writeLaTeX options document =
                 stUrl = False, stGraphics = False,
                 stLHS = False, stBook = writerChapters options,
                 stCsquotes = False, stHighlighting = False,
-                stFirstFrame = True, stIncremental = writerIncremental options }
+                stFirstFrame = True, stIncremental = writerIncremental options,
+                stInternalLinks = [] }
 
 pandocToLaTeX :: WriterOptions -> Pandoc -> State WriterState String
 pandocToLaTeX options (Pandoc (Meta title authors date) blocks) = do
+  -- see if there are internal links
+  let isInternalLink (Link _ ('#':xs,_))  = [xs]
+      isInternalLink _                    = []
+  modify $ \s -> s{ stInternalLinks = queryWith isInternalLink blocks }
   let template = writerTemplate options
   -- set stBook depending on documentclass
   let bookClasses = ["memoir","book","report","scrreprt","scrbook"]
@@ -430,7 +436,8 @@ sectionHeader ref level lst = do
   let stuffing = optional <> char '{' <> txt <> char '}'
   book <- liftM stBook get
   let level' = if book then level - 1 else level
-  let refLabel lab = (if (not . null) ref
+  internalLinks <- gets stInternalLinks
+  let refLabel lab = (if ref `elem` internalLinks
                          then text "\\hyperdef"
                                 <> braces empty
                                 <> braces (text ref)