Pipe tables: use full text width for tables with wrapping cells.

Previously we computed the column sizes based on the ratio
between the header lines and the text width (as set by `--columns`).
This meant that tables with very short header lines would be
very narrow. With this change, pipe tables with wrapping cells will
always take up the whole text width. The relative column widths
will still be determined by the ratio of header lines, but they
will be normalized to add up to 1.0.

MANUAL.txt

@@ -2637,7 +2637,10 @@ and lists, and cannot span multiple lines.  If a pipe table contains a
 row whose printable content is wider than the column width (see
 `--columns`), then the cell contents will wrap, with the
 relative cell widths determined by the widths of the separator
-lines.
+lines.  (In this case, the table will take up the full text
+width.)  If no lines are wider than column width, then
+cell contents will not be wrapped, and the cells will be sized
+to their contents.
 
 Note:  pandoc also recognizes pipe tables of the following
 form, as can be produced by Emacs' orgtbl-mode:

src/Text/Pandoc/Readers/Markdown.hs

@@ -1353,8 +1353,8 @@ pipeTable = try $ do
   numColumns <- getOption readerColumns
   let widths = if maxlength > numColumns
                   then map (\len ->
-                           fromIntegral (len + 1) / fromIntegral numColumns)
-                             seplengths
+                         fromIntegral (len + 1) / fromIntegral (sum seplengths))
+                         seplengths
                   else replicate (length aligns) 0.0
   return (aligns, widths, heads', sequence lines'')
 

test/pipe-tables.native

@@ -85,7 +85,7 @@
  ,[[Plain [Str "4"]]
   ,[Plain [Str "44"]]]]
 ,Para [Str "Long",Space,Str "pipe",Space,Str "table",Space,Str "with",Space,Str "relative",Space,Str "widths:"]
-,Table [] [AlignDefault,AlignDefault,AlignDefault] [0.125,0.1375,0.5]
+,Table [] [AlignDefault,AlignDefault,AlignDefault] [0.1639344262295082,0.18032786885245902,0.6557377049180328]
  [[Plain [Str "Default1"]]
  ,[Plain [Str "Default2"]]
  ,[Plain [Str "Default3"]]]