Disable underscore emphasis syntaxes for markdown

TODO.md

@@ -16,6 +16,7 @@
   - Time on their own lines
   - When selecting text and scrolling up, selection stops working after a while
     - Ensure all the text that should be copied is copied
+  - Mouse wheel scrolling speed in event list
 
   - Pressing backspace in composer sometimes doesn't work
   - Message order isn't preserved when sending a first message in a E2E
@@ -67,7 +68,7 @@
   - Combine events so they take less space
     - After combining is implemented, no need to hide profile changes anymore.
   - Replies
-  - Messages editing
+  - Messages editing and redaction
   - Code highlighting
   - Support GIF avatars and images
   - Adapt shortcuts flicking speed to font size and DPI
@@ -127,7 +128,7 @@
     - Edit/delete own devices
     - Request room keys from own other devices
     - Auto-trust accounts within the same client
-  - Uploads & proper http thumbnails
+  - Uploads
     - Reduce messages ListView cacheBuffer height once http thumbnails
       downloading is implemented 
   - Read receipts
@@ -163,8 +164,6 @@
       - Fetch all members when using the filter members bar
 
   - Direct chats category
-  - Markdown: don't turn #things (no space) and `thing\n---` into title,
-    disable `__` syntax for bold/italic
   - Better `<pre>` 
   - When inviting someone to direct chat, room is "Empty room" until accepted,
     it should be the peer's display name instead.

src/python/html_filter.py

@@ -7,8 +7,22 @@ import html_sanitizer.sanitizer as sanitizer
 from html_sanitizer.sanitizer import Sanitizer
 
 
-class MarkdownRenderer(mistune.Renderer):
-    pass
+class MarkdownInlineGrammar(mistune.InlineGrammar):
+    # Enable *word* but not _word_ syntaxes (TODO: config option for that)
+    emphasis        = re.compile(r"^\*((?:\*\*|[^\*])+?)\*(?!\*)")
+    double_emphasis = re.compile(r"^\*{2}([\s\S]+?)\*{2}(?!\*)")
+
+
+class MarkdownInlineLexer(mistune.InlineLexer):
+    grammar_class = MarkdownInlineGrammar
+
+
+    def output_double_emphasis(self, m):
+        return self.renderer.double_emphasis(self.output(m.group(1)))
+
+
+    def output_emphasis(self, m):
+        return self.renderer.emphasis(self.output(m.group(1)))
 
 
 class HtmlFilter:
@@ -41,7 +55,7 @@ class HtmlFilter:
 
         # hard_wrap: convert all \n to <br> without required two spaces
         self._markdown_to_html = mistune.Markdown(
-            hard_wrap=True, renderer=MarkdownRenderer(),
+            hard_wrap=True, inline=MarkdownInlineLexer,
         )
 
         self._markdown_to_html.block.default_rules = [