gridTables: properly handle columns with all empty cells.

See #10848.

src/Text/Pandoc/Writers/Shared.hs

@@ -325,7 +325,7 @@ extractColWidths opts rows = (currentwidths, fullwidths, minwidths)
    getCellWidths calcOffset c = replicate (cellColSpan c)
                                  (calcOffset c `div` (cellColSpan c) +
                                   calcOffset c `rem` (cellColSpan c))
-   fullwidths = getWidths (offset . cellContents)
+   fullwidths = getWidths (max 1 . offset . cellContents)
    currentwidths = getWidths cellWidth
    minwidths =
      case writerWrapText opts of
@@ -430,9 +430,7 @@ gridRows (x:xs) =
     -- be interpreted as an indented code block...even though it
     -- would look better to right-align right-aligned cells...
     -- (TODO: change this on parsing side?)
-    lblock (case cellWidth c of
-                  0 -> 16 -- TODO arbitrary
-                  w -> w) (cellContents c)
+    lblock (cellWidth c) (cellContents c)
 
   formatRow cs = vfill "| " <>
    hcat (intersperse (vfill " | ") (map renderCellContents cs)) <> vfill " |"

test/command/10848.md

@@ -57,3 +57,26 @@
 |   | K             |
 +---+---------------+
 ```
+
+```
+% pandoc -f html -t markdown-simple_tables-multiline_tables-pipe_tables
+<table>
+  <tbody>
+    <tr>
+      <td>a</td>
+      <td></td>
+    </tr>
+    <tr>
+      <td></td>
+      <td></td>
+    </tr>
+  </tbody>
+</table>
+^D
++---+---+
+| a |   |
++---+---+
+|   |   |
++---+---+
+```
+