Docx writer: handle table header using styles.

Instead of hard-coding the border and header cell vertical alignment,
we now let this be determined by the Table style, making use of
Word's "conditional formatting" for the table's first row.
For headerless tables, we use the tblLook element to tell Word
not to apply conditional first-row formatting.

Closes #7008.

data/docx/word/styles.xml

@@ -350,6 +350,21 @@
         <w:right w:w="108" w:type="dxa" />
       </w:tblCellMar>
     </w:tblPr>
+    <w:tblStylePr w:type="firstRow">
+      <w:tblPr>
+        <w:jc w:val="left"/>
+        <w:tblInd w:w="0" w:type="dxa"/>
+      </w:tblPr>
+      <w:trPr>
+        <w:jc w:val="left"/>
+      </w:trPr>
+      <w:tcPr>
+        <w:vAlign w:val="bottom"/>
+        <w:tcBorders>
+          <w:bottom w:val="single"/>
+        </w:tcBorders>
+      </w:tcPr>
+    </w:tblStylePr>
   </w:style>
   <w:style w:type="paragraph" w:customStyle="1" w:styleId="DefinitionTerm">
     <w:name w:val="Definition Term" />

src/Text/Pandoc/Writers/Docx.hs

@@ -1023,23 +1023,15 @@ blockToOpenXML' opts (Table _ blkCapt specs thead tbody tfoot) = do
             _ -> es ++ [Elem $ mknode "w:p" [] ()]
   headers' <- mapM cellToOpenXML $ zip aligns headers
   rows' <- mapM (mapM cellToOpenXML . zip aligns) rows
-  let borderProps = Elem $ mknode "w:tcPr" []
-                    [ mknode "w:tcBorders" []
-                      $ mknode "w:bottom" [("w:val","single")] ()
-                    , mknode "w:vAlign" [("w:val","bottom")] () ]
   compactStyle <- pStyleM "Compact"
   let emptyCell' = [Elem $ mknode "w:p" [] [mknode "w:pPr" [] [compactStyle]]]
-  let mkcell border contents = mknode "w:tc" []
-                            $ [ borderProps | border ] ++
-                            if null contents
-                               then emptyCell'
-                               else contents
-  let mkrow border cells =
+  let mkcell contents = mknode "w:tc" []
+                            $ if null contents
+                                 then emptyCell'
+                                 else contents
+  let mkrow cells =
          mknode "w:tr" [] $
-         [ mknode "w:trPr" []
-           [ mknode "w:cnfStyle" [("w:firstRow","1")] ()]
-         | border]
-         ++ map (mkcell border) cells
+           map mkcell cells
   let textwidth = 7920  -- 5.5 in in twips, 1/20 pt
   let fullrow = 5000 -- 100% specified in pct
   let rowwidth = fullrow * sum widths
@@ -1047,6 +1039,15 @@ blockToOpenXML' opts (Table _ blkCapt specs thead tbody tfoot) = do
                        [("w:w", show (floor (textwidth * w) :: Integer))] ()
   let hasHeader = not $ all null headers
   modify $ \s -> s { stInTable = False }
+  -- for compatibility with Word <= 2007, we include a val with a bitmask
+  -- 0×0020  Apply first row conditional formatting
+  -- 0×0040  Apply last row conditional formatting
+  -- 0×0080  Apply first column conditional formatting
+  -- 0×0100  Apply last column conditional formatting
+  -- 0×0200  Do not apply row banding conditional formatting
+  -- 0×0400  Do not apply column banding conditional formattin
+  let tblLookVal :: Int
+      tblLookVal = if hasHeader then 0x20 else 0
   return $
     caption' ++
     [Elem $
@@ -1059,15 +1060,17 @@ blockToOpenXML' opts (Table _ blkCapt specs thead tbody tfoot) = do
                                ,("w:firstColumn","0")
                                ,("w:lastColumn","0")
                                ,("w:noHBand","0")
-                               ,("w:noVBand","0")] () :
+                               ,("w:noVBand","0")
+                               ,("w:val", printf "%04x" tblLookVal)
+                               ] () :
           [ mknode "w:tblCaption" [("w:val", T.unpack captionStr)] ()
           | not (null caption) ] )
       : mknode "w:tblGrid" []
         (if all (==0) widths
             then []
             else map mkgridcol widths)
-      : [ mkrow True headers' | hasHeader ] ++
-      map (mkrow False) rows'
+      : [ mkrow headers' | hasHeader ] ++
+      map mkrow rows'
       )]
 blockToOpenXML' opts el
   | BulletList lst <- el = addOpenXMLList BulletMarker lst