Beagle SCM

LITE-031: GitHub Flavored Markdown extensions on the vendored parser

The input dialect that actually matters is GitHub's, not bare CommonMark: READMEs, issues and every .md in the wild carry tables, task lists, ~~struck~~ text and bare www. links. The vendored commonmark.js (LITE-030) implements none of them — GFM's reference implementation is the C cmark-gfm, with no official JS port. This ticket adds the four extensions on top of the vendored parser, layered as separate files wherever the upstream hook allows, so re-vendoring an upstream bump stays a script re-run.

Input

Context

The GFM spec is 0.29-gfm (2019-04-06), based on CommonMark 0.29 — older than the 0.31.2 core the vendored parser implements; the extensions are additive, the base differences are not this ticket's business. A text dump of the spec sits at ~/tmp/gfm.txt (fetched 2026-08-14; the live page is https://github.github.com/gfm/).

• Strikethrough: one OR two tildes both yield <del>; three or more yield nothing; a paragraph break stops the scan — an emphasis delimiter run, so it belongs in processEmphasis.
• Task list items: the item's FIRST block is a paragraph starting [ + (space | x | X) + ] + at least one whitespace char. A post-pass over the parsed list, not a parser change.
• Extended autolinks: markup-free. www. or http(s):// + valid domain (dot-separated alnum/_/- segments, at least one dot, no _ in the last two), then non-space non-< chars; trailing ?!.,:*_~ trimmed, unbalanced trailing ) trimmed only when the link ENDS in ), a trailing &name; shaped tail excluded, < ends it. Emails: alnum/./-/_/+, @, dotted alnum/-/_ domain, last char not -/_. Only at line start, after whitespace, or after *, _, ~, (.
• Tables: a leaf block — header row, a delimiter row of hyphen cells with optional leading/trailing : for alignment, then data rows; cells hold inlines only, never blocks; the header and delimiter cell counts must match or it is not a table.
• Not in scope: the tagfilter extension (nine tags escaped on HTML render) — StrictMark bans HTML inserts outright, so it can never fire.

Goals

The vendored parser accepts GFM and produces AST nodes the LITE-032 emitter can walk, with cmark-gfm agreeing on the rendered HTML for every ported example.

• Strikethrough, task lists and extended autolinks parse per the rules above, each with its GFM-spec examples as tests.
• Tables parse into a node the emitter can inspect — LITE-032 cannot represent one in StrictMark, but it must be able to SEE one to lint or lift it.
• Layering: new code in lite/mark/gfm-*.js; edits inside the five vendored files kept to the minimum hook and marked with the ticket code, so vendor.sh re-runs stay reviewable.

Constraints

• Ported tests: 500 lines MAX, inheriting gritzko's cap from LITE-030. The GFM spec is CC-BY-SA 4.0 — same rule, embed only the examples used, carry attribution and the license name.
• cmark-gfm is the HTML oracle, never a second JS parser: a JS oracle would share the emitter's bugs.
• ZERO quickjab edits.

WIP

Design decisions

• Strikethrough is the only genuine parser patch (a delimiter-run handler); the other three are a post-pass, a text-node sweep, and a leaf-block matcher.
• A task list item keeps the GFM marker's CHECKED state on the node, not the literal text: LITE-032 maps checked to -[v], unchecked to -[ ], and GFM's [x] never maps to StrictMark's -[x] (which means wontfix).

TODOs

• strikethrough delimiter run, one and two tildes, three+ inert
• task list post-pass, checked state on the node
• extended autolinks: www / url / email, with the trimming rules
• tables: delimiter-row match, alignment, inline-only cells
• test/mark/gfm legs, ≤500 lines, attribution + CC-BY-SA note
• cmark-gfm cross-check on the ported examples; report

Blockers and bummers

• A reported test/now leg-4 failure did NOT reproduce: that leg passes in both this worktree and LITE-030's, 42 checks. Nothing filed.

Outcome

Staged in work/LITE-031, 9 files, nothing posted. Orchestrator verification: test/mark/gfm/run.sh PASS at 49 checks, LITE-030's test/mark/run.sh still PASS at 66, and a document carrying all four extensions parses into the same node inventory cmark-gfm -t xml reports for it.

• Entry point is mark/gfm.js; the four parts are mark/gfm-{strike,table,tasklist,autolink}.js, 512 lines together.
• Vendored files carry 13 marked hook lines total — node.js 1 (the four node types become containers), blocks.js 4 (|/: in reMaybeSpecial, the fast-path opt-out, table_cell inlines), inlines.js 8 (tilde delimiter runs in processEmphasis).
• One divergence, documented in the test header: autolinks are a sweep over parsed text nodes, so * or a backtick inside a bare URL ends it where cmark-gfm swallows it. Every ported spec example still agrees.
• Suggested commit message: LITE-031: GFM strikethrough, task lists, autolinks, tables