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.

1 files changed, 132 insertions, 0 deletions

diff --git a/tests/test_syntax/inline/test_links.py b/tests/test_syntax/inline/test_links.py
new file mode 100644
index 0000000..3e8593f
--- /dev/null
+++ b/tests/test_syntax/inline/test_links.py
@@ -0,0 +1,132 @@
+# -*- coding: utf-8 -*-
+"""
+Python Markdown
+
+A Python implementation of John Gruber's Markdown.
+
+Documentation: https://python-markdown.github.io/
+GitHub: https://github.com/Python-Markdown/markdown/
+PyPI: https://pypi.org/project/Markdown/
+
+Started by Manfred Stienstra (http://www.dwerg.net/).
+Maintained for a few years by Yuri Takhteyev (http://www.freewisdom.org).
+Currently maintained by Waylan Limberg (https://github.com/waylan),
+Dmitry Shachnev (https://github.com/mitya57) and Isaac Muse (https://github.com/facelessuser).
+
+Copyright 2007-2018 The Python Markdown Project (v. 1.7 and later)
+Copyright 2004, 2005, 2006 Yuri Takhteyev (v. 0.2-1.6b)
+Copyright 2004 Manfred Stienstra (the original version)
+
+License: BSD (see LICENSE.md for details).
+"""
+
+from markdown.test_tools import TestCase
+
+
+class TestAdvancedLinks(TestCase):
+
+    def test_nested_square_brackets(self):
+        self.assertMarkdownRenders(
+            """[Text[[[[[[[]]]]]]][]](http://link.com) more text""",
+            """<p><a href="http://link.com">Text[[[[[[[]]]]]]][]</a> more text</p>"""
+        )
+
+    def test_nested_round_brackets(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/(((((((()))))))())) more text""",
+            """<p><a href="http://link.com/(((((((()))))))())">Text</a> more text</p>"""
+        )
+
+    def test_uneven_brackets_with_titles1(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/("title") more text""",
+            """<p><a href="http://link.com/(" title="title">Text</a> more text</p>"""
+        )
+
+    def test_uneven_brackets_with_titles2(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/('"title") more text""",
+            """<p><a href="http://link.com/('" title="title">Text</a> more text</p>"""
+        )
+
+    def test_uneven_brackets_with_titles3(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/("title)") more text""",
+            """<p><a href="http://link.com/(" title="title)">Text</a> more text</p>"""
+        )
+
+    def test_uneven_brackets_with_titles4(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/( "title") more text""",
+            """<p><a href="http://link.com/(" title="title">Text</a> more text</p>"""
+        )
+
+    def test_uneven_brackets_with_titles5(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/( "title)") more text""",
+            """<p><a href="http://link.com/(" title="title)">Text</a> more text</p>"""
+        )
+
+    def test_mixed_title_quotes1(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/'"title") more text""",
+            """<p><a href="http://link.com/'" title="title">Text</a> more text</p>"""
+        )
+
+    def test_mixed_title_quotes2(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/"'title') more text""",
+            """<p><a href="http://link.com/&quot;" title="title">Text</a> more text</p>"""
+        )
+
+    def test_mixed_title_quotes3(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/with spaces'"and quotes" 'and title') more text""",
+            """<p><a href="http://link.com/with spaces" title="&quot;and quotes&quot; 'and title">"""
+            """Text</a> more text</p>"""
+        )
+
+    def test_mixed_title_quotes4(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/with spaces'"and quotes" 'and title") more text""",
+            """<p><a href="http://link.com/with spaces'" title="and quotes&quot; 'and title">Text</a> more text</p>"""
+        )
+
+    def test_mixed_title_quotes5(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/with spaces '"and quotes" 'and title') more text""",
+            """<p><a href="http://link.com/with spaces" title="&quot;and quotes&quot; 'and title">"""
+            """Text</a> more text</p>"""
+        )
+
+    def test_mixed_title_quotes6(self):
+        self.assertMarkdownRenders(
+            """[Text](http://link.com/with spaces "and quotes" 'and title') more text""",
+            """<p><a href="http://link.com/with spaces &quot;and quotes&quot;" title="and title">"""
+            """Text</a> more text</p>"""
+        )
+
+    def test_single_quote(self):
+        self.assertMarkdownRenders(
+            """[test](link"notitle)""",
+            """<p><a href="link&quot;notitle">test</a></p>"""
+        )
+
+    def test_angle_with_mixed_title_quotes(self):
+        self.assertMarkdownRenders(
+            """[Text](<http://link.com/with spaces '"and quotes"> 'and title') more text""",
+            """<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>'
+        )