markdown: add ins (underline) and del (strikethrough) tags

app/utils/bleach_allowlist.py

@@ -1,7 +1,7 @@
 # Tags suitable for rendering markdown
 markdown_tags = [
     "h1", "h2", "h3", "h4", "h5", "h6",
-    "b", "i", "strong", "em", "tt",
+    "b", "i", "strong", "em", "tt", "ins", "del",
     "p", "br",
     "span", "div", "blockquote", "code", "pre", "hr",
     "ul", "ol", "li", "dd", "dt",

app/utils/filters/markdown.py

@@ -7,6 +7,7 @@ from markdown.extensions.toc import TocExtension, slugify_unicode
 from bleach import clean
 from app.utils.bleach_allowlist import markdown_tags, markdown_attrs
 
+from app.utils.markdown_extensions.del_ins import DelInsExtension
 from app.utils.markdown_extensions.pclinks import PCLinkExtension
 from app.utils.markdown_extensions.hardbreaks import HardBreakExtension
 from app.utils.markdown_extensions.escape_html import EscapeHtmlExtension
@@ -34,6 +35,7 @@ def md(text, prefix=None):
         # 'nl2br',
         'sane_lists',
         'tables',
+        DelInsExtension(),
         CodeHiliteExtension(linenums=True, use_pygments=True),
         EscapeHtmlExtension(),
         FootnoteExtension(UNIQUE_IDS=True),

app/utils/markdown_extensions/del_ins.py

@@ -0,0 +1,12 @@
+from markdown.extensions import Extension
+from markdown.inlinepatterns import SimpleTagPattern
+
+
+class DelInsExtension(Extension):
+    def extendMarkdown(self, md):
+        DEL_RE = r'(~~)(.*?)~~'
+        del_tag = SimpleTagPattern(DEL_RE, 'del')
+        md.inlinePatterns.register(del_tag, 'del', 55)
+        INS_RE = r'(__)(.*?)__'
+        ins_tag = SimpleTagPattern(INS_RE, 'ins')
+        md.inlinePatterns.register(ins_tag, 'ins', 55)