Fix double escaping of amp in attributes (#670)

Serializer should only escape & in attributes if not part of & 

Better regex avoid Unicode and `_` in amp detection.

In general, we don't want to escape already escaped content, but with code content, we want literal representations of escaped content, so have code content explicitly escape its content before placing in AtomicStrings.

Closes #669.

2 files changed, 12 insertions, 0 deletions

diff --git a/tests/test_syntax/inline/images.py b/tests/test_syntax/inline/test_images.py
index 52ce330..52ce330 100644
--- a/tests/test_syntax/inline/images.py
+++ b/tests/test_syntax/inline/test_images.py
diff --git a/tests/test_syntax/inline/links.py b/tests/test_syntax/inline/test_links.py
index d74bb75..3e8593f 100644
--- a/tests/test_syntax/inline/links.py
+++ b/tests/test_syntax/inline/test_links.py
@@ -118,3 +118,15 @@ class TestAdvancedLinks(TestCase):
             """<p><a href="http://link.com/with spaces '&quot;and quotes&quot;" title="and title">"""
             """Text</a> more text</p>"""
         )
+
+    def test_amp_in_url(self):
+        """Test amp in URLs."""
+
+        self.assertMarkdownRenders(
+            '[link](http://www.freewisdom.org/this&that)',
+            '<p><a href="http://www.freewisdom.org/this&amp;that">link</a></p>'
+        )
+        self.assertMarkdownRenders(
+            '[title](http://example.com/?a=1&amp;b=2)',
+            '<p><a href="http://example.com/?a=1&amp;b=2">title</a></p>'
+        )