Fix emails not getting linkified correctly

Fixes #398

tildes/tests/test_markdown.py

@@ -148,6 +148,14 @@ def test_https_link_linkified():
     assert '<a href="https://example.com">' in processed
 
 
+def test_mailto_link_linkified():
+    """Ensure that writing an email results in a working mailto link."""
+    markdown = "My email is email@example.com."
+    processed = convert_markdown_to_safe_html(markdown)
+
+    assert '<a href="mailto:email@example.com">' in processed
+
+
 def test_link_with_path_linkified():
     """Ensure a link with a path results in a link."""
     markdown = "So http://example.com/a/b_c_d/e too?"

tildes/tildes/lib/markdown.py

@@ -95,7 +95,7 @@ HTML_ATTRIBUTE_WHITELIST = {
     "code": allow_syntax_highlighting_classes,
     "span": allow_syntax_highlighting_classes,
 }
-PROTOCOL_WHITELIST = ("http", "https")
+PROTOCOL_WHITELIST = ("http", "https", "mailto")
 
 # Regex that finds ordered list markdown that was probably accidental - ones being
 # initiated by anything except "1." at the start of a post