Fix regression of single column tables (#540)

Single column tables are valid tables, so add back in the accidentally
removed functionality of allowing single column tables, but with one
exception -- table bodies should not render empty (an empty 
`<tbody>` is invalid HTML. Fixes #539.

3 files changed, 169 insertions, 11 deletions

diff --git a/markdown/extensions/tables.py b/markdown/extensions/tables.py
index ebe6ffa..ec3b6ac 100644
--- a/markdown/extensions/tables.py
+++ b/markdown/extensions/tables.py
@@ -21,6 +21,9 @@ from . import Extension
 from ..blockprocessors import BlockProcessor
 from ..util import etree
 import re
+PIPE_NONE = 0
+PIPE_LEFT = 1
+PIPE_RIGHT = 2
 
 
 class TableProcessor(BlockProcessor):
@@ -41,17 +44,33 @@ class TableProcessor(BlockProcessor):
         Keep border check and separator row do avoid repeating the work.
         """
         is_table = False
-        header = [row.strip() for row in block.split('\n')[0:2]]
-        if len(header) == 2:
-            self.border = header[0].startswith('|')
-            row = self._split_row(header[0])
-            is_table = len(row) > 1
+        rows = [row.strip() for row in block.split('\n')]
+        if len(rows) > 1:
+            header0 = rows[0]
+            self.border = PIPE_NONE
+            if header0.startswith('|'):
+                self.border |= PIPE_LEFT
+            if self.RE_END_BORDER.search(header0) is not None:
+                self.border |= PIPE_RIGHT
+            row = self._split_row(header0)
+            row0_len = len(row)
+            is_table = row0_len > 1
+
+            # Each row in a single column table needs at least one pipe.
+            if not is_table and row0_len == 1 and self.border:
+                for index in range(1, len(rows)):
+                    is_table = rows[index].startswith('|')
+                    if not is_table:
+                        is_table = self.RE_END_BORDER.search(rows[index]) is not None
+                    if not is_table:
+                        break
 
             if is_table:
-                row = self._split_row(header[1])
-                is_table = len(row) > 1 and set(''.join(row)) <= set('|:- ')
+                row = self._split_row(rows[1])
+                is_table = (len(row) == row0_len) and set(''.join(row)) <= set('|:- ')
                 if is_table:
                     self.separator = row
+
         return is_table
 
     def run(self, parent, blocks):
@@ -78,8 +97,20 @@ class TableProcessor(BlockProcessor):
         thead = etree.SubElement(table, 'thead')
         self._build_row(header, thead, align)
         tbody = etree.SubElement(table, 'tbody')
-        for row in rows:
-            self._build_row(row.strip(), tbody, align)
+        if len(rows) == 0:
+            # Handle empty table
+            self._build_empty_row(tbody, align)
+        else:
+            for row in rows:
+                self._build_row(row.strip(), tbody, align)
+
+    def _build_empty_row(self, parent, align):
+        """Build an empty row."""
+        tr = etree.SubElement(parent, 'tr')
+        count = len(align)
+        while count:
+            etree.SubElement(tr, 'td')
+            count -= 1
 
     def _build_row(self, row, parent, align):
         """ Given a row of text, build table cells. """
diff --git a/tests/extensions/extra/tables.html b/tests/extensions/extra/tables.html
index 2418c98..25dee48 100644
--- a/tests/extensions/extra/tables.html
+++ b/tests/extensions/extra/tables.html
@@ -167,7 +167,12 @@ Content Cell | Content Cell
 <th>Second Header</th>
 </tr>
 </thead>
-<tbody></tbody>
+<tbody>
+<tr>
+<td></td>
+<td></td>
+</tr>
+</tbody>
 </table>
 <p>More inline code block tests</p>
 <table>
@@ -375,4 +380,87 @@ Content Cell | Content Cell
 <td>\\<code>code</code></td>
 </tr>
 </tbody>
-</table>
\ No newline at end of file
+</table>
+<p>Single column tables</p>
+<table>
+<thead>
+<tr>
+<th>Is a Table</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td></td>
+</tr>
+</tbody>
+</table>
+<table>
+<thead>
+<tr>
+<th>Is a Table</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td></td>
+</tr>
+</tbody>
+</table>
+<table>
+<thead>
+<tr>
+<th>Is a Table</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td></td>
+</tr>
+</tbody>
+</table>
+<table>
+<thead>
+<tr>
+<th>Is a Table</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>row</td>
+</tr>
+</tbody>
+</table>
+<table>
+<thead>
+<tr>
+<th>Is a Table</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>row</td>
+</tr>
+</tbody>
+</table>
+<table>
+<thead>
+<tr>
+<th>Is a Table</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>row</td>
+</tr>
+</tbody>
+</table>
+<h2>| Is not a Table</h2>
+<p>| row</p>
+<h2>Is not a Table |</h2>
+<p>row            |</p>
+<p>| Is not a Table
+| --------------
+row</p>
+<p>Is not a Table |
+-------------- |
+row</p>
\ No newline at end of file
diff --git a/tests/extensions/extra/tables.txt b/tests/extensions/extra/tables.txt
index d766224..2dc4967 100644
--- a/tests/extensions/extra/tables.txt
+++ b/tests/extensions/extra/tables.txt
@@ -128,3 +128,42 @@ Should not be code | Should be code
 ------------------ | --------------
 \`Not code\`       | \\`code`
 \\\`Not code\\\`   | \\\\`code`
+
+Single column tables
+
+| Is a Table |
+| ---------- |
+
+| Is a Table
+| ----------
+
+Is a Table |
+---------- |
+
+| Is a Table |
+| ---------- |
+| row        |
+
+| Is a Table
+| ----------
+| row
+
+Is a Table |
+---------- |
+row        |
+
+| Is not a Table
+--------------
+| row
+
+Is not a Table |
+--------------
+row            |
+
+| Is not a Table
+| --------------
+row
+
+Is not a Table |
+-------------- |
+row