Reveal.js writer: restore old behavior for 2D nesting.

The fix to #6030 actually changed behavior, so that the
2D nesting occurred at slide level N-1 and N, instead of
at the top-level section.  This commit restores the 2.7.3 behavior.
If there are more than 2 levels, the top level is horizontal
and the rest are collapsed to vertical.

Closes #6032.

2 files changed, 36 insertions, 12 deletions

diff --git a/src/Text/Pandoc/Writers/HTML.hs b/src/Text/Pandoc/Writers/HTML.hs
index 095d55c0e..b739e2b2d 100644
--- a/src/Text/Pandoc/Writers/HTML.hs
+++ b/src/Text/Pandoc/Writers/HTML.hs
@@ -80,6 +80,7 @@ data WriterState = WriterState
     , stEPUBVersion  :: Maybe EPUBVersion -- ^ EPUB version if for epub
     , stSlideVariant :: HTMLSlideVariant
     , stSlideLevel   :: Int     -- ^ Slide level
+    , stInSection    :: Bool    -- ^ Content is in a section (revealjs)
     , stCodeBlockNum :: Int     -- ^ Number of code block
     }
 
@@ -90,6 +91,7 @@ defaultWriterState = WriterState {stNotes= [], stMath = False, stQuotes = False,
                                   stEPUBVersion = Nothing,
                                   stSlideVariant = NoSlides,
                                   stSlideLevel = 1,
+                                  stInSection = False,
                                   stCodeBlockNum = 0}
 
 -- Helpers to render HTML with the appropriate function.
@@ -662,8 +664,6 @@ blockToHtml opts (Div (ident, "section":dclasses, dkvs)
            else case splitBy isPause xs of
                      []     -> ([],[])
                      (z:zs) -> ([],z ++ concatMap inDiv zs)
-  titleContents <- blockListToHtml opts titleBlocks
-  innerContents <- blockListToHtml opts innerSecs
   let classes' = ordNub $
                   ["title-slide" | titleSlide] ++ ["slide" | slide] ++
                   ["section" | (slide || writerSectionDivs opts) &&
@@ -674,20 +674,26 @@ blockToHtml opts (Div (ident, "section":dclasses, dkvs)
                     then H5.section
                     else H.div
   let attr = (ident, classes', dkvs)
+  titleContents <- blockListToHtml opts titleBlocks
+  inSection <- gets stInSection
+  innerContents <- do
+    modify $ \st -> st{ stInSection = True }
+    res <- blockListToHtml opts innerSecs
+    modify $ \st -> st{ stInSection = inSection }
+    return res
   if titleSlide
      then do
        t <- addAttrs opts attr $
              secttag $ nl opts <> header' <> nl opts <> titleContents <> nl opts
+       -- ensure 2D nesting for revealjs, but only for one level;
+       -- revealjs doesn't like more than one level of nesting
        return $
-         -- ensure 2D nesting for revealjs, but only for one level;
-         -- revealjs doesn't like more than one level of nseting
-         (if slideVariant == RevealJsSlides && not (null innerSecs) &&
-             level == slideLevel - 1
-                then \z -> H5.section (nl opts <> z)
-                else id) $ t <> nl opts <>
-                           if null innerSecs
-                              then mempty
-                              else innerContents <> nl opts
+         if slideVariant == RevealJsSlides && not inSection &&
+              not (null innerSecs)
+            then H5.section (nl opts <> t <> nl opts <> innerContents)
+            else t <> nl opts <> if null innerSecs
+                                    then mempty
+                                    else innerContents <> nl opts
      else if writerSectionDivs opts || slide ||
               (hident /= ident && not (T.null hident || T.null ident)) ||
               (hclasses /= dclasses) || (hkvs /= dkvs)
diff --git a/test/command/6030.md b/test/command/6030.md
index 44a934a6a..e05bf6e7f 100644
--- a/test/command/6030.md
+++ b/test/command/6030.md
@@ -15,12 +15,20 @@ Three
 #### Four
 
 Four
+
+# New sec
+
+New sec
+
+## New sub
+
+New sub
 ^D
+<section>
 <section id="one" class="title-slide slide level1">
 <h1>One</h1>
 <p>One</p>
 </section>
-<section>
 <section id="two" class="title-slide slide level2">
 <h2>Two</h2>
 <p>Two</p>
@@ -32,6 +40,16 @@ Four
 <p>Four</p>
 </section>
 </section>
+<section>
+<section id="new-sec" class="title-slide slide level1">
+<h1>New sec</h1>
+<p>New sec</p>
+</section>
+<section id="new-sub" class="title-slide slide level2">
+<h2>New sub</h2>
+<p>New sub</p>
+</section>
+</section>
 ```
 
 ```