LaTeX writer: Mark span contents with label if span has an ID

Prepend `\label{span-id}` to span contents iff `span-id` is defined.

src/Text/Pandoc/Writers/LaTeX.hs

@@ -655,16 +655,20 @@ isQuoted _ = False
 -- | Convert inline element to LaTeX
 inlineToLaTeX :: Inline    -- ^ Inline to convert
               -> State WriterState Doc
-inlineToLaTeX (Span (_,classes,_) ils) = do
+inlineToLaTeX (Span (id',classes,_) ils) = do
   let noEmph = "csl-no-emph" `elem` classes
   let noStrong = "csl-no-strong" `elem` classes
   let noSmallCaps = "csl-no-smallcaps" `elem` classes
-  ((if noEmph then inCmd "textup" else id) .
-   (if noStrong then inCmd "textnormal" else id) .
-   (if noSmallCaps then inCmd "textnormal" else id) .
-   (if not (noEmph || noStrong || noSmallCaps)
-       then braces
-       else id)) `fmap` inlineListToLaTeX ils
+  let label' = if (null id')
+               then empty
+               else text "\\label" <> braces (text $ toLabel id')
+  fmap (label' <>)
+    ((if noEmph then inCmd "textup" else id) .
+     (if noStrong then inCmd "textnormal" else id) .
+     (if noSmallCaps then inCmd "textnormal" else id) .
+     (if not (noEmph || noStrong || noSmallCaps)
+         then braces
+         else id)) `fmap` inlineListToLaTeX ils
 inlineToLaTeX (Emph lst) =
   inlineListToLaTeX lst >>= return . inCmd "emph"
 inlineToLaTeX (Strong lst) =