Docx writer: properly handle display math in spans.

Closes #4826.  This isn't a complete solution, since other
nestings of display math may still cause problems, but it should
work for what is by far the most common case.

Note that this also involves an API change: `isDisplayMath`
is now exported from Text.Pandoc.Writers.Shared.

src/Text/Pandoc/Writers/Docx.hs

@@ -66,7 +66,8 @@ import Text.Pandoc.Readers.Docx.StyleMap
 import Text.Pandoc.Shared hiding (Element)
 import Text.Pandoc.Walk
 import Text.Pandoc.Writers.Math
-import Text.Pandoc.Writers.Shared (fixDisplayMath, metaValueToInlines)
+import Text.Pandoc.Writers.Shared (isDisplayMath, fixDisplayMath,
+                                   metaValueToInlines)
 import Text.Printf (printf)
 import Text.TeXMath
 import Text.XML.Light as XML
@@ -915,9 +916,10 @@ blockToOpenXML' opts (Para lst)
   | null lst && not (isEnabled Ext_empty_paragraphs opts) = return []
   | otherwise = do
       isFirstPara <- gets stFirstPara
-      paraProps <- getParaProps $ case lst of
-                                   [Math DisplayMath _] -> True
-                                   _                    -> False
+      let displayMathPara = case lst of
+                                 [x] -> isDisplayMath x
+                                 _   -> False
+      paraProps <- getParaProps displayMathPara
       bodyTextStyle <- pStyleM "Body Text"
       let paraProps' = case paraProps of
             [] | isFirstPara -> [mknode "w:pPr" []

src/Text/Pandoc/Writers/Shared.hs

@@ -38,6 +38,7 @@ module Text.Pandoc.Writers.Shared (
                      , resetField
                      , defField
                      , tagWithAttrs
+                     , isDisplayMath
                      , fixDisplayMath
                      , unsmartify
                      , gridTable
@@ -187,8 +188,9 @@ tagWithAttrs tag (ident,classes,kvs) = hsep
   ] <> ">"
 
 isDisplayMath :: Inline -> Bool
-isDisplayMath (Math DisplayMath _) = True
-isDisplayMath _                    = False
+isDisplayMath (Math DisplayMath _)          = True
+isDisplayMath (Span _ [Math DisplayMath _]) = True
+isDisplayMath _                             = False
 
 stripLeadingTrailingSpace :: [Inline] -> [Inline]
 stripLeadingTrailingSpace = go . reverse . go . reverse