✨ Add GFM autolink and composite GFM plugins

[chrisjsewell]

Summary

Adds two new plugins that require markdown-it-py >= 4.1.0:

gfm_autolink — GFM autolink literals

Implements the GFM autolinks extension
with three inline scanners:

• www. URLs (trigger char: w, via add_terminator_char)
• http:///https:///mailto:/xmpp: URLs (trigger char: :)
• Bare email addresses (trigger char: @)

Matching logic is ported from the Rust
gfm_autolinks
crate. Covers GFM spec examples 622–635 plus additional edge cases
(trailing delimiters, emphasis integration, parentheses balancing, etc.).

gfm — Composite GFM plugin

A single-call plugin that enables a GFM-like configuration:

• Tables (built-in)
• Strikethrough with single and double tildes (built-in)
• GFM autolinks (gfm_autolink)
• Task lists (built-in)
• Alerts (built-in)
• Footnotes (footnote_plugin, inline=False)
• Dollar math (optional, disabled by default)
• Front matter (optional, disabled by default)

Tag filtering is noted as a TODO.

Other changes

• tox.ini: test envs pin markdown-it-py>=4.1.0
• pyproject.toml: added pytest-timeout to testing extras

References

• GFM spec
• GitHub basic formatting syntax
• markdown-it-py 4.1.0 add_terminator_char API (PR ✨Allow plugins to register inline terminator characters markdown-it-py#391)

[codecov]

Codecov Report

❌ Patch coverage is 89.96764% with 31 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.68%. Comparing base (d11bdaf) to head (a2e265c).
⚠️ Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
mdit_py_plugins/gfm_autolink/_match.py	84.67%	21 Missing ⚠️
mdit_py_plugins/gfm_autolink/index.py	94.36%	8 Missing ⚠️
mdit_py_plugins/gfm/__init__.py	92.85%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #135      +/-   ##
==========================================
- Coverage   92.80%   92.68%   -0.12%     
==========================================
  Files          31       38       +7     
  Lines        1835     2257     +422     
==========================================
+ Hits         1703     2092     +389     
- Misses        132      165      +33     

Flag	Coverage Δ
pytests	92.68% <89.96%> (-0.12%)	⬇️

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[chrisjsewell]

Review

Summary

This PR adds two new plugins:

1. gfm_autolink — Implements the GFM autolink extension (bare www., http(s)://, mailto:, xmpp:, and bare email addresses). Ported from the Rust markdown_it_autolink crate.
2. gfm — A composite plugin that enables a full GFM-like experience (tables, strikethrough, autolinks, task lists, alerts, footnotes, and optionally dollar math / front matter).

All 32 tests pass.

---

Positives

• Clean port from the Rust crate with well-structured matching logic in _match.py
• Good test coverage with fixtures matching GFM spec examples (622–634) plus edge cases
• Composite gfm_plugin is a nice convenience API
• Proper version gating (markdown-it-py >= 4.1.0) with helpful error messages
• pytest-timeout addition is sensible for catching hangs

Issues / Suggestions

1. _isspace redundancy in _match.py (✅ fixed)

_SPACE_CHARS = frozenset(" \t\r\n\x00\x0b\x0c")

def _isspace(ch: str) -> bool:
    return ch in _SPACE_CHARS or ch == "\r" or ch == "\n"

\r and \n are already in _SPACE_CHARS, so the extra or checks are dead code. Should simplify to just return ch in _SPACE_CHARS.

2. gfm/__init__.py — docstring formatting (✅ fixed)

The docstring list has an oddly placed blank line between "Alerts" and "Footnotes" that breaks the list:

- Alerts (built-in, markdown-it-py >= 4.1.0)
- Footnotes (``[^label]`` references and definitions)
Optional extras:

Should be:

- Alerts (built-in, markdown-it-py >= 4.1.0)
- Footnotes (``[^label]`` references and definitions)

Optional extras:

3. gfm/__init__.py — md.options dict-style vs attribute-style

The composite plugin mixes dict-style (md.options["tasklists"] = True) and attribute-style access patterns. The test file test_gfm_autolink.py uses md.options.xhtmlOut = False while test_gfm.py uses md.options["xhtmlOut"] = False. These should be consistent — pick one style.

4. Missing __all__ in gfm/__init__.py

The gfm_autolink/__init__.py exports __all__, but gfm/__init__.py defines it. Actually gfm/__init__.py does have __all__ = ("gfm_plugin",) — that's fine.

5. Consider ReDoS safety

The _match.py functions use character-by-character scanning (no regex on user input for the heavy lifting), which is good. The single regex _PROTO_RE in index.py is anchored and operates on state.pending (bounded). Looks safe.

6. Minor: _autolink_delim could short-circuit

When link_end is 0 at the start, the while loop won't execute, but the initial for loop over data[:0] is a no-op too. Not a bug, just a nit.

---

Verdict

The implementation is solid and well-tested. The main actionable items are:

1. Fix the _isspace redundancy
2. Fix the docstring formatting