Preserve all blank lines in code blocks.

Fixes #183. Finally got this working properly. The key was
using a regex substitution with non-overlapping matches that
removed all whitespace from the begining of *all* blank lines
when normalizing whitespace.

Once I got that, I could simplfy the EmptyBlockProcessor
and easily output one or two blank lines appropriately.
A blank block gets two new lines (`'\n\n'`), while a
block which starts with a newline gets one.

2 files changed, 14 insertions, 14 deletions

diff --git a/markdown/blockprocessors.py b/markdown/blockprocessors.py
index b41df6a..8b41a37 100644
--- a/markdown/blockprocessors.py
+++ b/markdown/blockprocessors.py
@@ -495,27 +495,27 @@ class HRProcessor(BlockProcessor):
 
 
 class EmptyBlockProcessor(BlockProcessor):
-    """ Process blocks and start with an empty line. """
-
-    # Detect a block that only contains whitespace 
-    # or only whitespace on the first line.
-    RE = re.compile(r'^ *(\n|$)')
+    """ Process blocks that are empty or start with an empty line. """
 
     def test(self, parent, block):
-        return bool(self.RE.match(block))
+        return not block or block.startswith('\n')
 
     def run(self, parent, blocks):
         block = blocks.pop(0)
-        m = self.RE.match(block)
-        if m:
-            theRest = block[m.end():]
+        filler = '\n\n'
+        if block:
+            # Starts with empty line
+            # Only replace a single line.
+            filler = '\n'
+            # Save the rest for later.
+            theRest = block[1:]
             if theRest:
                 # Add remaining lines to master blocks for later.
                 blocks.insert(0, theRest)
-            sibling = self.lastChild(parent)
-            if sibling and sibling.tag == 'pre' and len(sibling) and sibling[0].tag == 'code':
-                # Last block is a codeblock. Append to preserve whitespace.
-                sibling[0].text = util.AtomicString('%s\n' % sibling[0].text )
+        sibling = self.lastChild(parent)
+        if sibling and sibling.tag == 'pre' and len(sibling) and sibling[0].tag == 'code':
+            # Last block is a codeblock. Append to preserve whitespace.
+            sibling[0].text = util.AtomicString('%s%s' % (sibling[0].text, filler))
 
 
 class ParagraphProcessor(BlockProcessor):
diff --git a/markdown/preprocessors.py b/markdown/preprocessors.py
index 3751264..6238303 100644
--- a/markdown/preprocessors.py
+++ b/markdown/preprocessors.py
@@ -50,7 +50,7 @@ class NormalizeWhitespace(Preprocessor):
         source = source.replace(util.STX, "").replace(util.ETX, "")
         source = source.replace("\r\n", "\n").replace("\r", "\n") + "\n\n"
         source = source.expandtabs(self.markdown.tab_length)
-        source = re.sub(r'\n +\n', '\n\n', source)
+        source = re.sub(r'(?<=\n) +\n', '\n', source)
         return source.split('\n')