Fix excessive backtracking when matching inline code blocks

[facelessuser]

Fixes #1617

Description

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[waylan]

Looks good to me. Curious if you checked how this affects performance.

[facelessuser]

I only ran it through the test script submitted in the issue. It at least resolved performance there. But we could do more tests if there is interest.

[facelessuser]

As far as performance. If we care, we could make it a little faster by removing the RE_TICKS usage and just iterating over the string. As this is already merged, that would need a separate PR. I won't worry about it unless this is requested, but figured I'd note it here.

diff --git a/markdown/inlinepatterns.py b/markdown/inlinepatterns.py
index 1a79bc4..0d8801a 100644
--- a/markdown/inlinepatterns.py
+++ b/markdown/inlinepatterns.py
@@ -447,29 +447,34 @@ class BacktickInlineProcessor(InlineProcessor):
     def find_code_spans(self, start: int, text: str) -> tuple[int, int] | None:
         """Find code spans."""
 
+        last = len(text)
+
         # Get the maximum starting ticks
-        m = self.RE_TICKS.match(text, start)
-        if m is None:  # pragma: no cover
+        max_ticks = 0
+        while start < last and text[start] == '`':
+            max_ticks += 1
+            start += 1
+
+        if not max_ticks:  # pragma: no cover
             # This is not ever expected to happen.
             return None
-        max_ticks = len(m.group(0))
 
-        start = m.end(0)
-        last = len(text)
         longest_span = 0
         end = 0
 
         # Find an ending span of backticks that matches our opening
         i = start
         while i < last:
-            m = self.RE_TICKS.match(text, i)
-            if m is None:
+            span_length = 0
+            while i < last and text[i] == '`':
+                span_length += 1
+                i += 1
+                continue
+            if not span_length:
                 i += 1
                 continue
 
             # Did we find the end?
-            i = m.end(0)
-            span_length = len(m.group(0))
             if max_ticks == span_length:
                 return start, i - span_length
 

[waylan]

As you already did the work, might as well use it. Feel free to open a new PR.

Thanks