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Fix quadratic rendering time for many inline links #1621

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Fix quadratic rendering time for many inline links #1621

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f03e1b5
Fix quadratic rendering time for many inline links
aryansk Aug 11, 2026
b745bba
Address review feedback on inline processor fix
aryansk Aug 11, 2026
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1 change: 1 addition & 0 deletions docs/changelog.md
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ See the [Contributing Guide](contributing.md) for details.
### Fixed

* Fix an issue with excessive backtracking when matching inline code blocks (#1617).
* Fix quadratic rendering time when a paragraph contains many inline links (#1619).
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## [3.10.3] - 2026-07-30

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9 changes: 7 additions & 2 deletions markdown/treeprocessors.py
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@waylan waylan Aug 11, 2026 •
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This changes the API for all inline patterns and processors. @facelessuser I think you have a better handle on this part of the code. Any input on that change here?

@aryansk aryansk Aug 11, 2026

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Thanks. I kept the search-index behavior change and documented it under Unreleased > Changed in b745bba, treating it as an inline-processor API/behavior change rather than a Fixed-only entry.

@facelessuser facelessuser Aug 13, 2026

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I do have some mild concerns about this change. We are assuming that because the API changed here without breaking things, others using this API won't be broken.

When we changed the API here in the first time, we did so in a way that was non-breaking, one you could opt into. This was done by providing a different class that could be checked.

It is possible that we may need to employ some method ot indicate this is a different version of the new way. I really need to do some testing to understand the implications of the change. I will have to do some testing with this over in Pymdown Extensions, where we have a number of plugins using the new style, so I can get a better idea of what the impact here is.

@facelessuser facelessuser Aug 13, 2026

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It seems that all the tests over on Pymdown Extensions passed with these changes, so that is a good sign.

@waylan waylan Aug 19, 2026

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@facelessuser did you intend to provide more input on this? Itis not clear to me if you had finished reviewing this.

@facelessuser facelessuser Aug 19, 2026

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Yeah, I've just been busy. My initial pass indicated that I don't "think" it'll break anything.

@facelessuser facelessuser Aug 19, 2026

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I can try to formally finish the review soon.

Original file line number Diff line number Diff line change
Expand Up @@ -323,12 +323,17 @@ def __applyPattern(
placeholder = self.__stashNode(node, pattern.type())

if new_style:
# Return the index just past the inserted placeholder so the
# next call scans only the unprocessed tail. Scanning from 0
# after every match makes repeated inline patterns quadratic.
return "{}{}{}".format(data[:start],
placeholder, data[end:]), True, 0
placeholder, data[end:]), True, start + len(placeholder)
else: # pragma: no cover
return "{}{}{}{}".format(leftData,
match.group(1),
placeholder, match.groups()[-1]), True, 0
placeholder, match.groups()[-1]), True, (
len(leftData) + len(match.group(1)) + len(placeholder)
)

def __build_ancestors(self, parent: etree.Element | None, parents: list[str]) -> None:
"""Build the ancestor list."""
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20 changes: 20 additions & 0 deletions tests/test_syntax/inline/test_links.py
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Expand Up @@ -21,6 +21,8 @@

from markdown.test_tools import TestCase

import time


class TestInlineLinks(TestCase):

Expand Down Expand Up @@ -434,3 +436,21 @@ def test_ref_round_brackets(self):
"""
)
)

def test_many_repeated_links(self):
# Regression test for #1619: rendering many inline links in one
# paragraph used to rescan the unprocessed text from the start after
# every match, making conversion quadratic in the number of links.
from markdown import Markdown

text = "[link](x)" * 8192
start = time.monotonic()
html = Markdown().convert(text)
elapsed = time.monotonic() - start

# The old implementation takes several seconds (or more on slow CI)
# for this input; the linear implementation finishes well under a
# second on any machine. Allow a generous ceiling to avoid flakes.
self.assertLess(elapsed, 5)
self.assertEqual(html.count("<a "), 8192)
self.assertEqual(html.count("</a>"), 8192)
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