Shared.hierarchicalize: improve handling of div and section structure.

Previously Divs were opaque to hierarchicalize, so headings
inside divs didn't get into the table of contents, for
example (#3057).

Now hierarchicalize treats Divs as sections when appropriate.
For example, these structures both yield a section and a
subsection:

``` html
<div>
<h1>one</h1>
<div>
<h2>two</h2>
</div>
</div>
```
``` html
<div>
<h1>one</h1>
<div>
<h1>two</h1>
</div>
</div>
```

Note that

``` html
<h1>one</h1>
<div>
<h2>two</h2>
</div>
<h1>three</h1>
```

gets parsed as the structure

    one
      two
    three

which may not always be desirable.

Closes #3057.

src/Text/Pandoc/Shared.hs

@@ -523,10 +523,21 @@ hierarchicalizeWithIds (Header level attr@(_,classes,_) title':xs) = do
   sectionContents' <- hierarchicalizeWithIds sectionContents
   rest' <- hierarchicalizeWithIds rest
   return $ Sec level newnum attr title' sectionContents' : rest'
-hierarchicalizeWithIds (Div ("refs",classes',kvs')
-                         (Header level (ident,classes,kvs) title' : xs):ys) =
-  hierarchicalizeWithIds (Header level (ident,"references":classes,kvs)
-                           title' : Div ("refs",classes',kvs') xs : ys)
+hierarchicalizeWithIds (Div attr@(_,classes',_)
+                         (Header level (_,classes,_) title' : xs):ys)
+  | not ("columns" `elem` classes')
+  , not ("column" `elem` classes') = do
+  lastnum <- S.get
+  let lastnum' = take level lastnum
+  let newnum = case length lastnum' of
+                    x | "unnumbered" `elem` classes -> []
+                      | x >= level -> init lastnum' ++ [last lastnum' + 1]
+                      | otherwise -> lastnum ++
+                           replicate (level - length lastnum - 1) 0 ++ [1]
+  unless (null newnum) $ S.put newnum
+  sectionContents' <- hierarchicalizeWithIds xs
+  rest' <- hierarchicalizeWithIds ys
+  return $ Sec level newnum attr title' sectionContents' : rest'
 hierarchicalizeWithIds (x:rest) = do
   rest' <- hierarchicalizeWithIds rest
   return $ Blk x : rest'

test/command/3057.md

@@ -0,0 +1,54 @@
+```
+% pandoc -f markdown -t docbook
+<div>
+# one
+<div>
+## two
+</div>
+</div>
+^D
+<section>
+  <title>one</title>
+  <section>
+    <title>two</title>
+    <para>
+    </para>
+  </section>
+</section>
+```
+
+```
+% pandoc -f markdown -t docbook
+<div>
+# one
+<div>
+# two
+</div>
+</div>
+^D
+<section>
+  <title>one</title>
+  <section>
+    <title>two</title>
+    <para>
+    </para>
+  </section>
+</section>
+```
+
+```
+% pandoc -f markdown -t docbook
+# one
+<div>
+# two
+</div>
+^D
+<section xml:id="one">
+  <title>one</title>
+  <section>
+    <title>two</title>
+    <para>
+    </para>
+  </section>
+</section>
+```