lepture
Exception caused in custom plugin altering parsing rules
We have a custom plugin that we use to disable all the parsing rules, except block_quote. The way we have implemented this is:
def plugin_disable_markdown(md):
"""This plugin disables most of the rules in mistune."""
md.block.rules = ['block_quote']
md.block.block_quote_rules = ['block_quote']
md.block.list_rules = ['block_quote']
md.inline.rules = ['inline_html', 'auto_link']
This causes an exception in the situation when the block_quote nesting depth increases the max_nesting_depth value (6 is the default in mistune).
So, a text like:
>> >> >> foo bar
will raise an exception like below (few lines of traceback is removed, full traceback can be found here)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/hyperkitty/templatetags/decorate.py", line 36, in render
return mark_safe(text_renderer(content))
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/markdown.py", line 110, in __call__
return self.parse(s)[0]
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/markdown.py", line 85, in parse
self.block.parse(state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 446, in parse
end_pos = self.parse_method(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/core.py", line 168, in parse_method
return func(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 369, in parse_block_quote
self.parse(child, rules)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 446, in parse
end_pos = self.parse_method(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/core.py", line 168, in parse_method
return func(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 369, in parse_block_quote
self.parse(child, rules)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 446, in parse
end_pos = self.parse_method(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/core.py", line 168, in parse_method
return func(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 369, in parse_block_quote
self.parse(child, rules)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 446, in parse
end_pos = self.parse_method(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/core.py", line 168, in parse_method
return func(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 369, in parse_block_quote
self.parse(child, rules)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 446, in parse
end_pos = self.parse_method(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/core.py", line 168, in parse_method
return func(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 369, in parse_block_quote
self.parse(child, rules)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 446, in parse
end_pos = self.parse_method(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/core.py", line 168, in parse_method
return func(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 369, in parse_block_quote
self.parse(child, rules)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/block_parser.py", line 446, in parse
end_pos = self.parse_method(m, state)
File "/opt/mailman/mm/venv/lib/python3.9/site-packages/mistune/core.py", line 167, in parse_method
func = self._methods[m.lastgroup]
KeyError: None
My suspicion is that after 5 levels of parsing blockquote, the block.block_quote_rules removes block_quote so that becomes an empty set of rules []. And since there aren't any rules m.lastgroup has no groups so it returns None value causing the above exception.
IMO, this can be guarded against with a None check of try-except (so control flow is altered only in case of special case of block_quote_rules being empty, which isn't typical).
Happy to submit a patch a try-except to guard works.
