Highlighting: highlighting now returns an Either rather than Maybe.

This allows us to display error information returned by the
skylighting library.

Display a warning if the highlighting library throws an error.

3 files changed, 29 insertions, 15 deletions

diff --git a/src/Text/Pandoc/Writers/Docx.hs b/src/Text/Pandoc/Writers/Docx.hs
index c182d42a3..04daf3b4b 100644
--- a/src/Text/Pandoc/Writers/Docx.hs
+++ b/src/Text/Pandoc/Writers/Docx.hs
@@ -1156,9 +1156,13 @@ inlineToOpenXML' opts (Code attrs str) = do
                                  [ rCustomStyle (show toktype) ]
                                , mknode "w:t" [("xml:space","preserve")] (T.unpack tok) ]
   withTextProp (rCustomStyle "VerbatimChar")
-    $ case writerHighlightStyle opts >> highlight formatOpenXML attrs str of
-           Just h  -> return h
-           Nothing -> unhighlighted
+    $ if isNothing (writerHighlightStyle opts)
+          then unhighlighted
+          else case highlight formatOpenXML attrs str of
+                    Right h  -> return h
+                    Left msg -> do
+                      unless (null msg) $ report $ CouldNotHighlight msg
+                      unhighlighted
 inlineToOpenXML' opts (Note bs) = do
   notes <- gets stFootnotes
   notenum <- (lift . lift) getUniqueId
diff --git a/src/Text/Pandoc/Writers/HTML.hs b/src/Text/Pandoc/Writers/HTML.hs
index fdf62dd56..10b782de7 100644
--- a/src/Text/Pandoc/Writers/HTML.hs
+++ b/src/Text/Pandoc/Writers/HTML.hs
@@ -644,11 +644,14 @@ blockToHtml opts (CodeBlock (id',classes,keyvals) rawCode) = do
       hlCode   = if isJust (writerHighlightStyle opts)
                     then highlight formatHtmlBlock
                             (id',classes',keyvals) adjCode
-                    else Nothing
+                    else Left ""
   case hlCode of
-         Nothing -> return $ addAttrs opts (id',classes,keyvals)
+         Left msg -> do
+           unless (null msg) $
+             report $ CouldNotHighlight msg
+           return $ addAttrs opts (id',classes,keyvals)
                            $ H.pre $ H.code $ toHtml adjCode
-         Just  h -> modify (\st -> st{ stHighlighting = True }) >>
+         Right h -> modify (\st -> st{ stHighlighting = True }) >>
                     return (addAttrs opts (id',[],keyvals) h)
 blockToHtml opts (BlockQuote blocks) = do
   -- in S5, treat list in blockquote specially
@@ -872,17 +875,19 @@ inlineToHtml opts inline = do
     (Emph lst)       -> inlineListToHtml opts lst >>= return . H.em
     (Strong lst)     -> inlineListToHtml opts lst >>= return . H.strong
     (Code attr str)  -> case hlCode of
-                             Nothing -> return
-                                        $ addAttrs opts attr
-                                        $ H.code $ strToHtml str
-                             Just  h -> do
+                             Left msg -> do
+                               unless (null msg) $
+                                 report $ CouldNotHighlight msg
+                               return $ addAttrs opts attr
+                                      $ H.code $ strToHtml str
+                             Right h -> do
                                modify $ \st -> st{ stHighlighting = True }
                                return $ addAttrs opts (id',[],keyvals) h
                         where (id',_,keyvals) = attr
                               hlCode = if isJust (writerHighlightStyle opts)
                                           then highlight formatHtmlInline
                                                    attr str
-                                          else Nothing
+                                          else Left ""
     (Strikeout lst)  -> inlineListToHtml opts lst >>=
                         return . H.del
     (SmallCaps lst)   -> inlineListToHtml opts lst >>=
diff --git a/src/Text/Pandoc/Writers/LaTeX.hs b/src/Text/Pandoc/Writers/LaTeX.hs
index 578c7017f..7e1970d01 100644
--- a/src/Text/Pandoc/Writers/LaTeX.hs
+++ b/src/Text/Pandoc/Writers/LaTeX.hs
@@ -540,8 +540,11 @@ blockToLaTeX (CodeBlock (identifier,classes,keyvalAttr) str) = do
                  "\\end{lstlisting}") $$ cr
   let highlightedCodeBlock =
         case highlight formatLaTeXBlock ("",classes,keyvalAttr) str of
-               Nothing -> rawCodeBlock
-               Just  h -> modify (\st -> st{ stHighlighting = True }) >>
+               Left msg -> do
+                 unless (null msg) $
+                   report $ CouldNotHighlight msg
+                 rawCodeBlock
+               Right h -> modify (\st -> st{ stHighlighting = True }) >>
                           return (flush $ linkAnchor $$ text (T.unpack h))
   case () of
      _ | isEnabled Ext_literate_haskell opts && "haskell" `elem` classes &&
@@ -958,8 +961,10 @@ inlineToLaTeX (Code (_,classes,_) str) = do
            return $ text $ "\\lstinline" ++ listingsopt ++ [chr] ++ str ++ [chr]
          highlightCode = do
            case highlight formatLaTeXInline ("",classes,[]) str of
-                  Nothing -> rawCode
-                  Just  h -> modify (\st -> st{ stHighlighting = True }) >>
+                  Left msg -> do
+                    unless (null msg) $ report $ CouldNotHighlight msg
+                    rawCode
+                  Right h -> modify (\st -> st{ stHighlighting = True }) >>
                              return (text (T.unpack h))
          rawCode = liftM (text . (\s -> "\\texttt{" ++ escapeSpaces s ++ "}"))
                           $ stringToLaTeX CodeString str