[Repo Assist] Improve CommonMark ATX heading compliance#1028
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- Reject ATX headings with no space after '#' (e.g. '#NoSpace' → paragraph) - Reject ATX headings with more than 6 '#' characters (→ paragraph) - Support 0–3 optional leading spaces before the opening '#' sequence - Fix empty heading body when entire content is a closing '###' sequence - Enable additional passing CommonMark spec sections: Blank lines, Inlines, Soft line breaks, Textual content, ATX headings (26 new test cases) - Update test expectations and reference HTML files to match CommonMark spec Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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@nojaf I'm OK with this. The code is not particularly pretty but if it's passing all tests plus the added tests I'm OK with it |
dsyme
approved these changes
Feb 26, 2026
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/repo-assist I have nitpicks on the tests. You changed the outcome of the existing test without adding a new one for properly formatted headers. There should be a tests for something like I would also like a rename of the test @dsyme , can't help myself, life is too short not to nitpick. |
- Rename 'Transform header 1 correctly' to 'ATX heading without space after hash is treated as paragraph' to better reflect what is being tested - Add new test 'ATX heading with space after hash is transformed to heading element' to verify that properly formatted ATX headings (e.g. '# Header 1', '## Header 2') produce heading elements Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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nojaf
approved these changes
Feb 26, 2026
nojaf
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🤖 This is a pull request created by Repo Assist, an automated AI assistant.
Closes #191
Summary
This PR improves CommonMark compliance for ATX headings in the Markdown parser. The changes fix four specific deviations from the [CommonMark spec for ATX headings]((spec.commonmark.org/redacted)
Changes to
MarkdownParser.fsThe
(|Heading|_|)active pattern's ATX heading case is rewritten to strictly follow CommonMark:#sequence —#NoSpaceand##Tagare now correctly rendered as paragraphs instead of headings.#characters —####### foo(7 hashes) is now a paragraph as required by the spec.## foo(up to 3 leading spaces) is now correctly recognised as a heading.### ###now correctly produces an empty<h3>rather than<h3>###</h3>.Enabled CommonMark spec sections (
CommonMarkSpecTest.fs)Five additional spec sections that were already 100% passing are now enabled, adding 26 new passing test cases:
ATX headings(19 tests)Blank lines(1 test)Inlines(1 test)Soft line breaks(2 tests)Textual content(3 tests)Updated tests
Markdown.fs: UpdatedTransform header 1 correctlyandTransform header 2 correctlyto reflect the correct CommonMark behavior (headings without a space after#are paragraphs).Tight blocks.html,line-endings-*.html): Updated to reflect that#Header/##Headerwithout a space are paragraphs rather than headings.Test Status
✅ All 220 Markdown tests pass (26 new, 194 pre-existing — 0 failures).
✅ All 101 Literate tests pass.
✅ Build succeeds.