Remove ``` support from code fence

Supporting ``` as a code fence marker complicates the auto-fence
closing, and as per a discussion with Keegan on code-review@, it
is not worth the extra complexity.

(imported from commit 405afb95c4295a02f4677181456caf9d49913ac4)

zephyr/lib/bugdown/fenced_code.py

@@ -49,18 +49,6 @@ Language tags:
     <pre><code class="python"># Some python code
     </code></pre>
 
-Optionally backticks instead of tildes as per how github's code block markdown is identified:
-
-    >>> text = '''
-    ... `````
-    ... # Arbitrary code
-    ... ~~~~~ # these tildes will not close the block
-    ... `````'''
-    >>> print markdown.markdown(text, extensions=['fenced_code'])
-    <pre><code># Arbitrary code
-    ~~~~~ # these tildes will not close the block
-    </code></pre>
-
 Copyright 2007-2008 [Waylan Limberg](http://achinghead.com/).
 
 Project website: <http://packages.python.org/Markdown/extensions/fenced_code_blocks.html>
@@ -80,13 +68,11 @@ import markdown
 from zephyr.lib.bugdown.codehilite import CodeHilite, CodeHiliteExtension
 
 # Global vars
-FENCE_RE = re.compile(r'(?P<fence>^(?:~{3,}|`{3,}))[ ]*(\{?\.?(?P<lang>[a-zA-Z0-9_+-]*)\}?)', re.MULTILINE|re.DOTALL)
+FENCE_RE = re.compile(r'(?P<fence>^(?:~{3,}))[ ]*(\{?\.?(?P<lang>[a-zA-Z0-9_+-]*)\}?)', re.MULTILINE|re.DOTALL)
 FENCED_BLOCK_RE = re.compile( \
-    r'(?P<fence>^(?:~{3,}|`{3,}))[ ]*(\{?\.?(?P<lang>[a-zA-Z0-9_+-]*)\}?)?[ ]*\n(?P<code>.*?)(?<=\n)(?P=fence)[ ]*$',
+    r'(?P<fence>^(?:~{3,}))[ ]*(\{?\.?(?P<lang>[a-zA-Z0-9_+-]*)\}?)?[ ]*\n(?P<code>.*?)(?<=\n)(?P=fence)[ ]*$',
     re.MULTILINE|re.DOTALL
     )
-# Match an inline code expression in markdown: `x=1` or ``def foo(self): bar`` for example
-INLINE_CODE_RE = re.compile(r'(?P<fence>`+).+?(?P=fence)')
 CODE_WRAP = '<pre><code%s>%s</code></pre>'
 LANG_TAG = ' class="%s"'
 
@@ -125,14 +111,7 @@ class FencedBlockPreprocessor(markdown.preprocessors.Preprocessor):
         while 1:
             m = FENCED_BLOCK_RE.search(text)
             if not m:
-                # If there is an inline code block, skip past it
-                start = 0
-                inline = INLINE_CODE_RE.search(text, start)
-                while inline:
-                    start = inline.end()
-                    inline = INLINE_CODE_RE.search(text, start)
-
-                fence = FENCE_RE.search(text, start)
+                fence = FENCE_RE.search(text)
                 if fence:
                     # If we found a starting fence but no ending fence,
                     # then we add a closing fence before the two newlines that

zephyr/tests.py

@@ -1131,7 +1131,7 @@ speak</span><span class="p">(</span><span class="bp">self</span><span class="p">
     def test_codeblock_multiline(self):
         fenced_code = \
 """Hamlet once said
-````
+~~~~
 def func():
     x = 1
 
@@ -1139,7 +1139,7 @@ def func():
     y = 2
 
     z = 3
-````
+~~~~
 And all was good."""
 
         expected_convert = \