Shared: Improve makeSections.

Previously it would sometimes create doubled section divs.
By leaving the inner heading's id on the heading itself, and
then consolidating the inner and outer section divs, we can
avoid this undesirable result.

Closes #11745.

src/Text/Pandoc/Shared.hs

@@ -569,16 +569,25 @@ makeSectionsWithOffsets numoffsets numbering mbBaseLevel bs =
       | all (\case
                Header level' _ _ -> level' > level
                _                 -> True) ys
-      , "column" `notElem` dclasses
-      , "columns" `notElem` dclasses
-      , "fragment" `notElem` dclasses = do
+      , "section" `elem` dclasses
+        || ("column" `notElem` dclasses &&
+            "columns" `notElem` dclasses &&
+            "fragment" `notElem` dclasses &&
+            "cell" `notElem` dclasses) = do
     inner <- go (Header level hattr title':ys)
     rest <- go xs
     return $
       case inner of
-            [Div divattr'@(dident',_,_) zs]
-              | T.null dident || T.null dident' || dident == dident'
-              -> Div (combineAttr divattr' divattr) zs : rest
+            [Div divattr'@(dident',_,_) zs@(Header level' hattr' title'' : zs')]
+              | dident == dident'
+                -> Div (combineAttr divattr' divattr) zs : rest
+              | (_,dclasses',dkvs) <- combineAttr divattr' divattr
+              , ("",hclasses,hkvs) <- hattr'
+                -> if T.null dident
+                      then Div (dident',dclasses',dkvs) zs : rest
+                      else Div (dident,dclasses',dkvs)
+                             (Header level' (dident',hclasses,hkvs) title''
+                               : zs') : rest
             _ -> Div divattr inner : rest
   go (Div attr xs : rest) = do
     xs' <- go xs

test/command/11745.md

@@ -0,0 +1,26 @@
+```
+% pandoc --section-divs
+# Book Title
+
+::: {#ch1 .section}
+## Chapter 1
+Hello world.
+:::
+
+::: {#ch2 .section}
+## Chapter 2
+Goodbye world.
+:::
+^D
+<section id="book-title" class="level1">
+<h1>Book Title</h1>
+<section id="ch1" class="level2">
+<h2 id="chapter-1">Chapter 1</h2>
+<p>Hello world.</p>
+</section>
+<section id="ch2" class="level2">
+<h2 id="chapter-2">Chapter 2</h2>
+<p>Goodbye world.</p>
+</section>
+</section>
+```