Simplified slide creation in HTML writer.

A horizontal rule now gets transformed into an empty H1 header
before 'hierarchicalize' is called.

If the document that does not begin with an H1 header, an
empty one is provided.

This avoids the need for kludgy raw HTML.

Also, the 'titleslide' class is added to any section containing
just a title:

----

----

1 files changed, 18 insertions, 26 deletions

diff --git a/src/Text/Pandoc/Writers/HTML.hs b/src/Text/Pandoc/Writers/HTML.hs
index 25904e93f..6bc911fbd 100644
--- a/src/Text/Pandoc/Writers/HTML.hs
+++ b/src/Text/Pandoc/Writers/HTML.hs
@@ -106,18 +106,17 @@ pandocToHtml opts (Pandoc (Meta title' authors' date') blocks) = do
   date <- if standalone
              then inlineListToHtml opts date'
              else return noHtml
+  let splitHrule (HorizontalRule : Header 1 xs : ys)
+                                       = Header 1 xs : splitHrule ys
+      splitHrule (HorizontalRule : xs) = Header 1 [] : splitHrule xs
+      splitHrule (x : xs)              = x : splitHrule xs
+      splitHrule []                    = []
+  let ensureStartWithH1 bs@(Header 1 _:_) = bs
+      ensureStartWithH1 bs                = Header 1 [] : bs
   let sects = hierarchicalize $
               if writerSlideVariant opts == NoSlides
                  then blocks
-                 else case blocks of
-                           (Header 1 _ : _) -> blocks
-                           _                ->
-                                let isL1 (Header 1 _) = True
-                                    isL1 _            = False
-                                    (preBlocks, rest) = break isL1 blocks
-                                in  (RawBlock "html" "<div class=\"slide\">" :
-                                    preBlocks) ++ (RawBlock "html" "</div>" :
-                                    rest)
+                 else ensureStartWithH1 $ splitHrule blocks
   toc <- if writerTableOfContents opts
             then tableOfContents opts sects
             else return Nothing
@@ -226,13 +225,6 @@ elementToListItem opts (Sec _ num id' headerText subsecs) = do
 
 -- | Convert an Element to Html.
 elementToHtml :: WriterOptions -> Element -> State WriterState Html
-elementToHtml opts (Blk HorizontalRule)
-  | writerSlideVariant opts == S5Slides ||
-    writerSlideVariant opts == SlidySlides =
-  return $ primHtml "</div>" +++ nl opts +++ primHtml "<div class=\"slide\">"
-elementToHtml opts (Blk HorizontalRule)
-  | writerSlideVariant opts == DZSlides =
-  return $ primHtml "</section>" +++ nl opts +++ primHtml "<section>"
 elementToHtml opts (Blk block) = blockToHtml opts block
 elementToHtml opts (Sec level num id' title' elements) = do
   modify $ \st -> st{stSecNum = num}  -- update section number
@@ -244,17 +236,17 @@ elementToHtml opts (Sec level num id' title' elements) = do
                                   writerSlideVariant opts == S5Slides)]
   let stuff = header'' : innerContents
   let slide = writerSlideVariant opts /= NoSlides && level == 1
-  let stuff' =  if (writerSlideVariant opts == S5Slides ||
-                    writerSlideVariant opts == SlidySlides) && level == 1
-                   then [thediv ! [theclass "slide"] <<
-                          (nl opts : intersperse (nl opts) stuff ++ [nl opts])]
-                   else intersperse (nl opts) stuff
-  let inNl x = nl opts : x ++ [nl opts]
-  return $ if writerSectionDivs opts || writerSlideVariant opts == DZSlides
+  let titleSlide = slide && null elements
+  let classes = [theclass "titleslide" | titleSlide] ++
+                [theclass "slide" | slide]
+  let inNl x = nl opts : intersperse (nl opts) x ++ [nl opts]
+  return $ if writerSectionDivs opts || slide
               then if writerHtml5 opts
-                      then tag "section" ! [prefixedId opts id'] << inNl stuff'
-                      else thediv ! [prefixedId opts id'] << inNl stuff'
-              else toHtmlFromList stuff'
+                      then tag "section" ! (prefixedId opts id' : classes)
+                                << inNl stuff
+                      else thediv ! (prefixedId opts id' : classes)
+                                << inNl stuff
+              else toHtmlFromList $ intersperse (nl opts) stuff
 
 -- | Convert list of Note blocks to a footnote <div>.
 -- Assumes notes are sorted.