LaTeX writer: Put `~` before header in item text.

Because of the built-in line skip, LaTeX can't handle a section header
as the first element in a list item. (To be precise, it can't handle it
if the list immediately follows a section header, but the instance is
rare enough that we can afford to be a bit more general). This puts a
non-breaking space before the header to solve this problem. We won't see
this space, since the header skips a line before printing anyway.

The output is ugly in LaTeX and this structure seems like it should
probably be avoided. But it is valid HTML and native pandoc, so we
should have some sort of typesettable representation in LaTeX.

1 files changed, 12 insertions, 2 deletions

diff --git a/src/Text/Pandoc/Writers/LaTeX.hs b/src/Text/Pandoc/Writers/LaTeX.hs
index acbe8a48d..8e3befe19 100644
--- a/src/Text/Pandoc/Writers/LaTeX.hs
+++ b/src/Text/Pandoc/Writers/LaTeX.hs
@@ -572,7 +572,13 @@ tableCellToLaTeX header (width, align, blocks) = do
                           $ reverse ns)
 
 listItemToLaTeX :: [Block] -> State WriterState Doc
-listItemToLaTeX lst = blockListToLaTeX lst >>= return .  (text "\\item" $$) .
+listItemToLaTeX lst
+  -- we need to put some text before a header if it's the first
+  -- element in an item. This will look ugly in LaTeX regardless, but
+  -- this will keep the typesetter from throwing an error.
+  | ((Header _ _ _) :_) <- lst =
+    blockListToLaTeX lst >>= return . (text "\\item ~" $$) . (nest 2)
+  | otherwise = blockListToLaTeX lst >>= return .  (text "\\item" $$) .
                       (nest 2)
 
 defListItemToLaTeX :: ([Inline], [[Block]]) -> State WriterState Doc
@@ -586,7 +592,11 @@ defListItemToLaTeX (term, defs) = do
                     then braces term'
                     else term'
     def'  <- liftM vsep $ mapM blockListToLaTeX defs
-    return $ "\\item" <> brackets term'' $$ def'
+    return $ case defs of
+     (((Header _ _ _) : _) : _) ->
+       "\\item" <> brackets term'' <> " ~ " $$ def'
+     _                          ->
+       "\\item" <> brackets term'' $$ def'
 
 -- | Craft the section header, inserting the secton reference, if supplied.
 sectionHeader :: Bool    -- True for unnumbered