Commit2a7d24ebRecorded31 Jul 2026Repositorysigil-markdown

sigil-markdown 0.9.4: stop publishing HTML comments

Message

A <!-- ... --> block fell through to the paragraph case and rendered as escaped visible text. That published RELEASES.md's authoring notes onto usesigil.org, from a comment whose own first line read "this comment is not published".

Block-level comments, single and multi-line, are now consumed and emitted as nothing. Per CommonMark an unterminated comment runs to end of document; that is asserted by a test so it is deliberate rather than a surprise. Inline comments are still passed through - this parser has no inline raw-HTML handling at all.

32/32, up from 27. Sabotage-tested: neutering the detector fails exactly the three comment tests, and the two CONTROL tests (prose with angle brackets, a document with no comment) stay green, so they would catch a stripper that deleted too much.

Changed
 CHANGELOG.md           |  6 ++++++
 package.sgl            |  2 +-
 src/sigil/markdown.sgl | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 test/test-markdown.sgl | 34 +++++++++++++++++++++++++++++++++-
 4 files changed, 86 insertions(+), 2 deletions(-)
Diff
CHANGELOG.mdmodified
@@ -7,6 +7,12 @@ All notable changes to this project will be documented in this file.
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The format is based on [Keep a Changelog](https://keepachangelog.com/),
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and this project adheres to [Semantic Versioning](https://semver.org/).
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## [0.9.4] - 2026-07-31
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### Fixed
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- HTML comments are no longer rendered. A `<!-- ... -->` block previously fell through to the paragraph case and appeared as escaped, visible text, so authoring notes intended for source readers were published. Both single-line and multi-line comments are now consumed and emitted as nothing. Per CommonMark, an unterminated comment runs to the end of the document; that behaviour is deliberate and covered by a test. Inline comments inside a paragraph are still passed through, since this parser has no inline raw-HTML handling.
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## [0.9.3] - 2026-07-30
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### Fixed
package.sglmodified
@@ -5,7 +5,7 @@
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(package
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name: "sigil-markdown"
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version: "0.9.3"
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version: "0.9.4"
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sigil: "^0.17"
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description: "Markdown and frontmatter parser"
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url: "https://codeberg.org/sigil/sigil-markdown"
src/sigil/markdown.sglmodified
@@ -98,6 +98,24 @@
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(loop start (+ i 1) lines))))))
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;; Check if line is a horizontal rule (---, ***, ___)
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;; Does LINE open an HTML comment block? CommonMark HTML block type 2.
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;; Leading spaces are allowed, as with the other block starts.
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(define (html-comment-start? line)
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(let ((trimmed (string-trim line)))
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(and (>= (string-length trimmed) 4)
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(string=? (substring trimmed 0 4) "<!--"))))
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;; Does LINE contain the comment terminator? Per CommonMark the block ends
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;; on the line containing `-->`, INCLUDING the opening line, so a one-line
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;; `<!-- x -->` is a complete block.
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(define (html-comment-end? line)
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(let ((len (string-length line)))
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(let loop ((i 0))
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(cond
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((> (+ i 3) len) #f)
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((string=? (substring line i (+ i 3)) "-->") #t)
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(else (loop (+ i 1)))))))
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(define (horizontal-rule? line)
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(let ((trimmed (string-trim line)))
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(and (>= (string-length trimmed) 3)
@@ -386,6 +404,34 @@
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((string-blank? line)
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(loop rest blocks))
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;; HTML comment block - consumed and emitted as nothing.
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;;
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;; Must be tested BEFORE the paragraph fallthrough, which is
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;; what previously rendered `<!-- ... -->` as escaped visible
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;; text. That shipped authoring notes onto usesigil.org's
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;; Releases page, from a comment whose own first line read
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;; "this comment is not published".
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;;
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;; Per CommonMark, an UNTERMINATED comment runs to end of
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;; document. That is the spec and other tools agree, so we
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;; match it rather than inventing a safer-looking rule that
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;; would render differently elsewhere. It does mean a stray
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;; `<!--` silently eats the remainder; the alternative is
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;; content that renders one way here and another way in every
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;; other renderer, which is worse.
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;;
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;; Scope: BLOCK-level comments only. An inline `<!-- -->` in
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;; the middle of a paragraph is still passed through as text,
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;; because this parser has no inline raw-HTML handling at all.
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((html-comment-start? line)
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(if (html-comment-end? line)
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(loop rest blocks)
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(let skip-loop ((rest rest))
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(cond
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((null? rest) (reverse blocks))
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((html-comment-end? (car rest)) (loop (cdr rest) blocks))
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(else (skip-loop (cdr rest)))))))
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;; ATX Header
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((parse-atx-header line)
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=> (lambda (header)
test/test-markdown.sglmodified
@@ -264,4 +264,36 @@
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(inner (car (filter pair? (cdr top))))
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(deeper (car (filter pair? (cdr (car (sxml-content inner)))))))
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(assert-equal 'ul (sxml-tag inner))
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(assert-equal 'ul (sxml-tag deeper)))))
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(assert-equal 'ul (sxml-tag deeper))))
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;; HTML comments. Before 0.9.4 these fell through to the paragraph case and
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;; rendered as escaped VISIBLE TEXT — which published a RELEASES.md authoring
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;; note onto usesigil.org, from a comment whose own first line read "this
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;; comment is not published".
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;;
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;; The two CONTROL tests below are the point: it is easy to write a stripper
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;; that also eats ordinary prose containing angle brackets, and a suite that
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;; only checked "the comment is gone" would pass for a parser that deleted
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;; far too much.
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(test "multi-line HTML comment is not rendered"
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(let ((doc (markdown->sxml "# T\n\n<!--\n hidden note\n-->\n\nVisible.\n")))
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(assert-equal '(document (h1 "T") (p "Visible.")) doc)))
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(test "single-line HTML comment is not rendered"
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(let ((doc (markdown->sxml "# T\n\n<!-- hidden -->\n\nVisible.\n")))
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(assert-equal '(document (h1 "T") (p "Visible.")) doc)))
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(test "CONTROL: prose containing angle brackets survives"
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(let ((doc (markdown->sxml "# T\n\na < b and c > d\n")))
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(assert-equal '(document (h1 "T") (p "a < b and c > d")) doc)))
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(test "CONTROL: a document with no comment is unchanged"
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(let ((doc (markdown->sxml "# T\n\nVisible only.\n")))
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(assert-equal '(document (h1 "T") (p "Visible only.")) doc)))
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;; CommonMark: an unterminated comment runs to end of document. Asserted so
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;; the behaviour is deliberate and discoverable rather than a surprise.
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(test "unterminated comment consumes the rest, per CommonMark"
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(let ((doc (markdown->sxml "# T\n\n<!-- oops\n\nSwallowed.\n")))
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(assert-equal '(document (h1 "T")) doc))))