RST writer: Improve spacing for tables with no width information.

If a simple table would be too wide, we use a grid table.
The code for generating grid tables has been adjusted to
give more intelligent column widths when widths aren't
given. (This also affects the markdown writer.)

Closes #5899.

4 files changed, 94 insertions, 15 deletions

diff --git a/src/Text/Pandoc/Writers/RST.hs b/src/Text/Pandoc/Writers/RST.hs
index 4a3b1b066..dc732b0e6 100644
--- a/src/Text/Pandoc/Writers/RST.hs
+++ b/src/Text/Pandoc/Writers/RST.hs
@@ -296,7 +296,13 @@ blockToRST (Table caption aligns widths headers rows) = do
   opts <- gets stOptions
   let isSimple = all (== 0) widths
   tbl <- if isSimple
-            then simpleTable opts blocksToDoc headers rows
+            then do
+              tbl' <- simpleTable opts blocksToDoc headers rows
+              if offset tbl' > writerColumns opts
+                 then gridTable opts blocksToDoc (all null headers)
+                      (map (const AlignDefault) aligns) widths
+                      headers rows
+                 else return tbl'
             else gridTable opts blocksToDoc (all null headers)
                   (map (const AlignDefault) aligns) widths
                   headers rows
diff --git a/src/Text/Pandoc/Writers/Shared.hs b/src/Text/Pandoc/Writers/Shared.hs
index 39035832f..0161db506 100644
--- a/src/Text/Pandoc/Writers/Shared.hs
+++ b/src/Text/Pandoc/Writers/Shared.hs
@@ -229,8 +229,7 @@ gridTable opts blocksToDoc headless aligns widths headers rows = do
   -- handleGivenWidths wraps the given blocks in order for them to fit
   -- in cells with given widths. the returned content can be
   -- concatenated with borders and frames
-  let handleGivenWidths widths' = do
-        let widthsInChars' = officialWidthsInChars widths'
+  let handleGivenWidthsInChars widthsInChars' = do
         -- replace page width (in columns) in the options with a
         -- given width if smaller (adjusting by two)
         let useWidth w = opts{writerColumns = min (w - 2) (writerColumns opts)}
@@ -241,6 +240,8 @@ gridTable opts blocksToDoc headless aligns widths headers rows = do
              (\cs -> zipWithM blocksToDoc columnOptions cs)
              rows
         return (widthsInChars', rawHeaders', rawRows')
+  let handleGivenWidths widths' = handleGivenWidthsInChars
+                                     (officialWidthsInChars widths')
   -- handleFullWidths tries to wrap cells to the page width or even
   -- more in cases where `--wrap=none`. thus the content here is left
   -- as wide as possible
@@ -262,9 +263,22 @@ gridTable opts blocksToDoc headless aligns widths headers rows = do
   let handleZeroWidths widths' = do
         (widthsInChars', rawHeaders', rawRows') <- handleFullWidths widths'
         if foldl' (+) 0 widthsInChars' > writerColumns opts
-           then -- use even widths
-                handleGivenWidths
-                  (replicate numcols (1.0 / fromIntegral numcols) :: [Double])
+           then do -- use even widths except for thin columns
+             let evenCols  = max 5
+                              (((writerColumns opts - 1) `div` numcols) - 3)
+             let (numToExpand, colsToExpand) =
+                   foldr (\w (n, tot) -> if w < evenCols
+                                            then (n, tot + (evenCols - w))
+                                            else (n + 1, tot))
+                                   (0,0) widthsInChars'
+             let expandAllowance = colsToExpand `div` numToExpand
+             let newWidthsInChars = map (\w -> if w < evenCols
+                                                  then w
+                                                  else min
+                                                       (evenCols + expandAllowance)
+                                                       w)
+                                        widthsInChars'
+             handleGivenWidthsInChars newWidthsInChars
            else return (widthsInChars', rawHeaders', rawRows')
   -- render the contents of header and row cells differently depending
   -- on command line options, widths given in this specific table, and
diff --git a/test/command/5128.md b/test/command/5128.md
index 2ab051c04..35866547e 100644
--- a/test/command/5128.md
+++ b/test/command/5128.md
@@ -1,5 +1,5 @@
 ```
-pandoc -f org -t rst
+pandoc -f org -t rst --columns=78
 | Option | Meaning                                                                                                                                                                                                    |
 |--------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | =<=    | Left alignment, additional characters are added to the right (default for string).                                                                                                                         |
@@ -7,12 +7,20 @@ pandoc -f org -t rst
 | =^=     | Centered , the same amount of characters is added to the left and the right.                                                                                                                               |
 | ===      | Padding. If a numeric value is printed with a sign, then additional characters are added after the sign. Otherwise it behaves like "=>=". This option is only available for numbers (default for numbers). |
 ^D
-====== ============================================================================================================================================================================================================
-Option Meaning
-====== ============================================================================================================================================================================================================
-``<``  Left alignment, additional characters are added to the right (default for string).
-``>``  Right alignment, additional characters are added to the left.
-``^``  Centered , the same amount of characters is added to the left and the right.
-``=``  Padding. If a numeric value is printed with a sign, then additional characters are added after the sign. Otherwise it behaves like "``>``". This option is only available for numbers (default for numbers).
-====== ============================================================================================================================================================================================================
++--------+------------------------------------------------------------------+
+| Option | Meaning                                                          |
++========+==================================================================+
+| ``<``  | Left alignment, additional characters are added to the right     |
+|        | (default for string).                                            |
++--------+------------------------------------------------------------------+
+| ``>``  | Right alignment, additional characters are added to the left.    |
++--------+------------------------------------------------------------------+
+| ``^``  | Centered , the same amount of characters is added to the left    |
+|        | and the right.                                                   |
++--------+------------------------------------------------------------------+
+| ``=``  | Padding. If a numeric value is printed with a sign, then         |
+|        | additional characters are added after the sign. Otherwise it     |
+|        | behaves like "``>``". This option is only available for numbers  |
+|        | (default for numbers).                                           |
++--------+------------------------------------------------------------------+
 ```
diff --git a/test/command/5899.md b/test/command/5899.md
new file mode 100644
index 000000000..28e020d20
--- /dev/null
+++ b/test/command/5899.md
@@ -0,0 +1,51 @@
+```
+% pandoc -f html -t rst
+<html>
+  <body>
+    <ul>
+      <li>A list of stuff with a table inside
+        <table>
+          <thead>
+            <tr>
+              <th>First</th><th>Second</th><th>Third</th>
+            </tr>
+          </thead>
+          <tbody>
+            <tr>
+              <td>First</td>
+              <td>
+                The big long table cell.
+                The big long table cell.
+                The big long table cell.
+                The big long table cell.
+                The big long table cell.
+                The big long table cell.
+                The big long table cell.
+                The big long table cell.
+                The big long table cell.
+                The big long table cell.
+              </td>
+              <td>Third</td>
+            </tr>
+          </tbody>
+        </table>
+      </li>
+      <li>Another list item</li>
+    </ul>
+  </body>
+</html>
+^D
+-  A list of stuff with a table inside
+
+   +-------+----------------------------------------------------+-------+
+   | First | Second                                             | Third |
+   +=======+====================================================+=======+
+   | First | The big long table cell. The big long table cell.  | Third |
+   |       | The big long table cell. The big long table cell.  |       |
+   |       | The big long table cell. The big long table cell.  |       |
+   |       | The big long table cell. The big long table cell.  |       |
+   |       | The big long table cell. The big long table cell.  |       |
+   +-------+----------------------------------------------------+-------+
+
+-  Another list item
+ ```