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2606171403_parity-layer0-list-quote-rules.md

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id 2606171403
title Parity parse-skip: migrate the Layer-0 list and blockquote rules
status ✅
summary Add a nil-AST path to the parity rules that read list and blockquote structure — MDS014 blank-line-around-lists, MDS016 list-indent, MDS045 list-marker-style, MDS046 ordered-list-numbering, MDS061 list-marker-space, MDS059 blockquote-whitespace, MDS067 callout-type — each gated byte-identical to the AST across the corpus.
model opus
depends-on
2606171258

Parity parse-skip: migrate the Layer-0 list and blockquote rules

Goal

Move the list and blockquote parity rules onto the Layer-0 block scan, so they no longer force the parse.

Background

List and quote spans are the subtle case. CommonMark list parsing folds in loose vs tight lists, nesting, and lazy continuation, so a Layer-0 span boundary can drift from the AST. The Layer-0 scanner emits one BlockList span per list-item run and one BlockQuote span, and descends into their bodies. There is no per-item span kind; a rule that needs item-level granularity walks the list span's body lines itself.

Each rule needs the marker shape (- / * / +, or 1. / 1)), the marker indent, and the inter-item spacing — all line-level facts. MDS067 callout-type reads only a blockquote's first line, so it lives here too. Verify the span boundaries match the AST before trusting them.

Rule Name Reads
MDS014 blank-line-around-lists top-level list span edges
MDS016 list-indent item marker indent
MDS045 list-marker-style bullet marker character
MDS046 ordered-list-numbering ordered marker sequence
MDS061 list-marker-space spaces after the marker
MDS059 blockquote-whitespace > marker spacing
MDS067 callout-type blockquote first line

Tasks

For each rule:

  1. First confirm the relevant span boundary matches the AST across the corpus. Add the nil-AST path only once it does.
  2. Add a CheckBlock (or span walk) reusing the existing extraction. Keep the diagnostic byte-identical: same line, column, message.
  3. Regenerate the walk audit and sync the embedded rulelayer copy.
  4. Add a TestCheck_NilASTMatchesAST unit test covering nested lists, a loose list, and a list that holds a code fence.

Acceptance Criteria

  • Each rule resolves to Layer 0 (audit A-no-skipping).
  • TestLayer0Gate_CorpusDiagnosticsEquivalence green with them on.
  • go test ./... passes.

Implementation notes

The seven rules now branch in Check. A parsed File takes the AST path. A nil-AST File (f.AST == nil) takes a Layer-0 path. The blockquote rules walk the scanner's BlockQuote spans directly. MDS059 detects the MD028 blank-line gap between adjacent spans; MDS067 reads the [!type] token off each span's first line.

The four list rules share a new line-based list parser, internal/rules/listscan. It re-derives goldmark's list facts from f.Lines. The facts are: the item marker line, the nesting level, the list ordered-ness and Start, the per-item literal number, the multi-block flag, and the top-level list's first and last line. The block scanner cannot supply these. It collapses a list into one single-line BlockList span per marker, with no nesting.

listscan.Parse is checked byte-for-byte against the goldmark AST in listscan_ast_test.go. The test corpus spans the rules' bad fixtures plus nested, loose, and code-fence cases.

Each rule extracts a shared verdict/itemVerdict helper that both paths drive, so the two paths agree by construction. A TestCheck_NilASTMatchesAST per rule pins it on nested lists, a loose list, and a list holding a code fence.

listscan does not handle tab-indented lists, lists nested inside block quotes, or HTML-block list interruption. The parse-skip gate still forces an AST parse for any source containing a list or a > (layer0SkipEligible conditions 4 and 5). So the nil-AST path for these rules runs only in the audit and unit tests today. Relaxing those gate conditions is the dependent benchmark work, not this plan.