pandoc-ir-migrate

name	pandoc-ir-migrate
description	Incrementally migrate Panache's Pandoc-dialect inline parsing onto the unified inline IR (currently CommonMark-only) one bounded sub-task at a time, verifying every CST divergence against pandoc-native before fixing or deferring.

Use this skill when asked to advance the Pandoc-dialect inline IR migration, fix a specific Pandoc emphasis / inline regression introduced by an IR-migration step, or pick "the next best phase" to work on.

Scope boundaries

• Target is the inline IR pipeline at crates/panache-parser/src/parser/inlines/inline_ir.rs and its consumers in crates/panache-parser/src/parser/inlines/core.rs. The goal is to retire crates/panache-parser/src/parser/inlines/delimiter_stack.rs and the legacy recursive-descent emphasis path (try_parse_emphasis, try_parse_one/two/three, parse_until_closer_with_nested_*) once both dialects share the IR.
• This is a long-horizon effort (8 phases — see "Phased plan" below). Each session moves one phase or sub-task forward; do not try to land sweeping rewrites in one go.
• Inline IR changes for the Pandoc dialect must not regress CommonMark conformance. The conformance harness at crates/panache-parser/tests/commonmark/allowlist.txt is the load-bearing guard — re-run it every session.
• Pandoc-native is the behavioral reference for the migration. The legacy try_parse_emphasis recursive-descent path may itself diverge from pandoc on edge cases; do NOT preserve a legacy fixture's output when it conflicts with pandoc -f markdown -t native. See "Pandoc vs legacy fixture trap" below.
• Do not commit a session whose diff regresses any test that was green at the start. Defer the unfinished work to a follow-up session and document in RECAP.md instead. The user has explicitly asked for this discipline; follow it strictly.

Related rules to read first

These project rules apply directly to this skill's work; read them before starting if you haven't already loaded them this session:

• .claude/rules/parser.md — Dialect vs Extensions split, dialect pandoc-verification requirement, CST losslessness, the TEXT-coalescence-vs-structural-diff distinction (added for this skill), and the pandoc-native-is-the-reference rule.
• .claude/rules/integration-tests.md — formatter golden cases live under top-level tests/fixtures/cases/ and are wired in tests/golden_cases.rs; parser-only cases live under crates/panache-parser/tests/fixtures/cases/ and wire into crates/panache-parser/tests/golden_parser_cases.rs. Do not mix them.
• .claude/rules/commonmark.md — Pandoc-IR changes that affect the shared inline_ir.rs algorithm must keep Dialect::CommonMark byte-identical; the conformance allowlist is the regression guard.

Harness noise to ignore inside this skill

The runtime occasionally injects a system-reminder nudging you to use TaskCreate / TaskUpdate for tracking. For most sub-tasks the workflow below is linear (probe → classify → fix → fixture → recap), so task tools add overhead without value. Skip them for migration sessions unless the user explicitly asks for a task list. The exception is multi-phase sessions (rare) — there a task list per phase helps.

Phased plan

The migration is bounded by 9 phases. Pick one (or part of one) per session. The latest phase status lives in RECAP.md.

Phase 0 — Thread Dialect through inline_ir's compute_flanking, process_emphasis*. Stub branch points; no behavior change.

Phase 1 (keystone) — Pandoc emphasis on the IR. build_full_plans skips process_brackets under Pandoc; build_ir recognises Pandoc opaque constructs (math $...$, inline links, ref links, footnote refs [^id], citations [@cite], bracketed spans [text]{attrs}, inline footnotes ^[note], native spans <span>...</span>) as ConstructKind::PandocOpaque events so emphasis can't pair across them. Activate dialect gates in flanking + matching + cascade. Drop the dispatcher fork in parse_inline_text_recursive / parse_inline_text. Widen populate_refdef_labels to both dialects.

Phase 2 — Move ^[note] and <span>...</span> recognition out of the dispatcher's ordered-try chain in parse_inline_range_impl into build_ir as Construct events. Pure additive; no algorithm change.

Phase 3 — [^id] footnote refs into IR scan as Construct::FootnoteReference.

Phase 4 — [@cite] bracketed citations + bare @cite into IR scan as Construct::BracketedCitation / Construct::BareCitation.

Phase 5 — Bracketed spans [text]{attrs} into IR process_brackets (first phase that changes process_brackets). Adds a new BracketResolutionKind::BracketedSpan variant and gates bracket_says_resolved on kind.

Phase 6 — Pandoc links/images dispatched IR-first. Originally planned as full BracketPlan-driven dispatch with deactivate_earlier_link_openers gated on CommonMark only; recap-(viii) verified against pandoc-native that the gating mechanism would have been wrong (pandoc-native does NOT allow nested links — outer wins, inner literal — so the rule isn't "don't deactivate," it's "deactivate inner instead of outer"). Phase 6 instead followed the Phase 2-5 ConstructPlan pattern: a new ConstructKind::PandocLinkOrImage that drives IR-first dispatch through the dispatcher's existing try_parse_* chain, with the legacy [/![ branches in parse_inline_range_impl gated on Dialect::CommonMark. Pure additive; the three pre-existing pandoc-native divergences below are preserved and addressed in Phase 8.

Phase 7 — Delete the legacy emphasis path: try_parse_emphasis*, try_parse_one/two/three, parse_until_closer_with_nested_*, parse_inline_range, the recursive-descent emphasis branch in parse_inline_range_impl. Delete the delimiter_stack module; relocate EmphasisPlan / DelimChar / EmphasisKind into inline_ir.rs.

Phase 8 (final) — Pandoc bracket emission on the IR's BracketPlan. Enable process_brackets under Dialect::Pandoc (currently CommonMark-only in build_full_plans) with two Pandoc-aware semantic differences:

1. Outer-wins link-in-link suppression. When a Pandoc bracket resolves, mark all bracket events inside its range as inactive so they emit literal. This is the OPPOSITE of CommonMark §6.3's deactivate_earlier_link_openers (inner-wins). NOT a toggle of that flag — a different rule.
2. Refdef-aware shortcut resolution under Pandoc. Replace is_commonmark short-circuit in process_brackets's shortcut path with refdef-map consultation for both dialects. Pandoc's shape-only reference_resolves = true is wrong; it produces malformed LINK nodes for unresolved shortcuts and steals inner */_ chars from the emphasis scanner.

This fixes the three pre-existing pandoc-native divergences noted in recap-(viii):

• [foo] with no refdef parses as malformed LINK → should be literal (Str "[foo]").
• *foo [bar* baz] produces TEXT + partial LINK → should be all literal (refdef miss frees the * for emphasis pairing).
• [link [inner](u2)](u1) allows nested LINK → should be outer-wins with inner literal.

Cleanup once Phase 8 lands: ConstructKind::PandocLinkOrImage and its ConstructDispo variant become unused (folded into BracketDispo::Open); the CM-gated [/![ legacy dispatcher branches in parse_inline_range_impl either stay (as the CM emission path) or get unified with the IR-driven path. Pandoc- specific golden fixtures for the three bug cases land under crates/panache-parser/tests/fixtures/cases/, verified against pandoc -f markdown -t native.

Migration-complete invariant: after Phase 8, no Pandoc inline construct depends on the dispatcher's try_parse_* chain for resolution decisions. The dispatcher recognizers are still called to parse a matched range into a CST subtree, but "what is this byte range?" is answered exclusively by the IR. That is the end-state of this migration.

The full design rationale lives in /home/jola/.claude/plans/let-s-create-a-plan-noble-barto.md (initial migration plan; treat as historical reference once the recap has captured each phase's outcome).

Key files

• crates/panache-parser/src/parser/inlines/inline_ir.rs — IR scan, bracket resolution, emphasis pass; primary site for dialect parameterization. Where most edits land.
• crates/panache-parser/src/parser/inlines/core.rs — dispatcher, emission walk; ~1500 lines disappear in Phase 7.
• crates/panache-parser/src/parser/inlines/delimiter_stack.rs — legacy emphasis plan builder. Exposes EmphasisPlan / DelimChar / EmphasisKind types still used by the IR's build_emphasis_plan. Deleted in Phase 7.
• crates/panache-parser/src/parser/inlines/{citations,bracketed_spans,inline_footnotes,native_spans,math,links}.rs — try_parse_* recognizers reused by build_ir's opaque-construct scan. Don't duplicate logic; call into them.
• crates/panache-parser/src/parser.rs — populate_refdef_labels (widened to both dialects in Phase 1).
• crates/panache-parser/src/options.rs — Dialect, Extensions, ParserOptions. No signature changes; consult for flag defaults.
• crates/panache-parser/tests/commonmark/allowlist.txt — CommonMark conformance regression guard. Must stay green.
• crates/panache-parser/tests/fixtures/cases/ — parser golden scenarios (paired CommonMark/Pandoc fixtures live here).
• tests/fixtures/cases/ — formatter golden scenarios (only add a CommonMark-flavor case here when the parser change produces a different block sequence than the Pandoc path).

Failure buckets

Every Pandoc-dialect IR migration regression falls into one of these. Classify before editing.

• TEXT-coalescence diff — old fixture had multiple adjacent TEXT spans (e.g. TEXT@0..5 "**foo" + TEXT@5..6 "*"); new IR produces a single coalesced TEXT (TEXT@0..6 "**foo*"). Same bytes, same structure, no STRONG/EMPHASIS/etc node difference. Benign; snapshot update is safe after confirming the structural shape matches pandoc-native (see "Pandoc vs legacy fixture trap"). Don't invent a fix to preserve the split — the IR's coalescence is an improvement, not a bug.
• Missing dialect gate — Pandoc-specific rule (intraword underscore hard-rule, mod-3 disable, asymmetric (1,2)/(2,1) rejection, opener count >= 4 rejection, triple-emph nesting flip, Pandoc closer-flanking-free) isn't applied. Fix: add or correct the branch in compute_flanking / process_emphasis_in_range_filtered.
• Missing opaque construct — IR's build_ir doesn't recognise a Pandoc inline construct, so emphasis pairs across its content (or worse, the dispatcher's later parse re-claims bytes already consumed by emphasis, breaking losslessness). Fix: add the recognizer to build_ir under !is_commonmark, emitting ConstructKind::PandocOpaque (or the phase-specific kind). Losslessness is the canary — if the parser-crate suite shows "tree text does not match input", losslessness has broken and a missing opaque construct is the most likely cause.
• Cascade-amenable algorithmic divergence — IR matches an emphasis pair that Pandoc rejects because of an unmatched same-character run between opener and closer (*foo**bar*, **foo *bar** baz*). Fix: ensure the run is flanking-eligible (both can_open && can_close) so pandoc_cascade_invalidate catches it. If the cascade rule itself needs widening, do so carefully — the trap below documents one over-broad version.
• Scoped-pass-needed algorithmic divergence — nested strong-of-emph or emph-of-strong cases where the IR's left-to-right closer walk matches the wrong pair (**foo *bar* baz** should be STRONG[foo, EM[bar], baz]; *foo **bar* baz** should be *foo + STRONG[bar* baz]; ***foo **bar** baz*** should be EM[STRONG[foo], "bar", STRONG[baz]]). Fix needs strong-first pass preference + scoped emphasis recursion on each strong-matched inner range. Don't try the "two-pass + un-remove-between" shortcut — it breaks the pair-crossing invariant (see trap below). The structurally clean approach is recursive scoped passes in build_full_plans analogous to the bracket scoped pass for CommonMark.
• Genuine algorithmic divergence beyond IR expressivity — pandoc recursive-descent semantics that the delim-stack can't express even with scoped passes. Defer; document in RECAP.md and (if meaningful) in crates/panache-parser/tests/commonmark/blocked.txt or a new pandoc-equivalent file.

Pandoc vs legacy fixture trap

The legacy try_parse_emphasis path is not the migration's reference. It approximates pandoc-native but has its own bugs and quirks. When the new IR output differs from a legacy fixture, do NOT default to "preserve the fixture". Instead:

printf '<input>' | pandoc -f markdown -t native > /tmp/pd.txt
printf '<input>' | pandoc -f commonmark -t native > /tmp/cm.txt

• New IR output matches /tmp/pd.txt (Pandoc native) → fixture is wrong; update the fixture (and snapshot) to the IR output. Note the prior fixture as a legacy-parser bug in RECAP.md.
• New IR output differs from /tmp/pd.txt AND old fixture matched /tmp/pd.txt → regression; fix the IR.
• New IR output differs from /tmp/pd.txt AND old fixture also differed (both wrong, in different ways) → fix toward pandoc-native; don't preserve either old behavior.
• TEXT-coalescence diffs are below this verification's resolution (pandoc-native doesn't pin TEXT-token granularity). For these, confirm structural elements (Strong, Emph, Link, etc.) match in count and nesting; if so, update the snapshot and move on.

Trap: two-pass + un-remove-between breaks pair crossing

A natural-looking but wrong attempt at "strong-first preference": run a first pass over count >= 2 closers, mark removed[] on between-events as usual, then un-remove them between passes so a second pass can match nested count == 1 emphasis. This breaks the pair-crossing invariant: in pass 2, an emphasis can pair with an opener whose strong partner is INSIDE the emphasis's range, producing an EM whose markers cross a STRONG's markers. The emission walk then produces invalid CST.

Correct approach: scoped emphasis passes. After a strong match in pass 1, run process_emphasis_in_range on the inner event range (open_idx + 1, close_idx) WITH its own state (separate count, source_start, removed arrays). Mirrors the bracket scoped pass for CommonMark in build_full_plans (lines 1247-1306 of inline_ir.rs). The state separation is the crucial bit; reusing the outer pass's state is what causes the crossing.

Trap: cascade-rule over-invalidation

The cascade rule (pandoc_cascade_invalidate) checks for "unmatched same-ch run between matched pair". The flanking-eligibility filter on those runs MUST be can_open && can_close (both true), not can_open || can_close. The || version invalidates legitimate matches when intraword _ (e.g. _foo_bar_baz_) sits between an opener and closer; pandoc-native does pair the outer _s and treats the inner _s as literal text inside emphasis content. The recursive-descent path's "if inner attempt fails, outer fails" semantics only fires when the inner construct could actually have opened/closed — i.e. both flanking sides are eligible.

Algorithmic toolbox

These are the dialect-aware levers in inline_ir.rs. When fixing a regression, identify which lever applies before editing.

• compute_flanking branches on Dialect:
  • CommonMark: §6.2 left/right-flanking exact rules.
  • Pandoc: can_open = !followed_by_ws; can_close = true (no flanking gate — pandoc-markdown's ender is count-only). Underscore intraword hard-rule applies on top: _ adjacent to alphanumeric on either side cannot open/close on that side.
• pandoc_reject opener-finder gate: rejects (1,2), (2,1), and count_o >= 4. Verified against pandoc-native: (1,3), (3,1), (2,3), (3,2), and any (≤3, 4+) DO match.
• Mod-3 rejection (CommonMark §6.2 rule 9): gated on is_commonmark; disabled under Pandoc.
• Consume rule for triple-emph nesting: when count[o] >= 3 && count[c] >= 3 AND !is_commonmark, consume = 1 first (emph innermost) instead of consume = 2 (CommonMark default, strong outermost). This produces STRONG(EM(...)) for ***x*** under Pandoc.
• pandoc_cascade_invalidate: post-pass that walks resolved matches and invalidates any pair containing an unmatched same-ch run with both can_open && can_close. Iterates to fixed point.
• Pandoc opaque construct scan in build_ir: under !is_commonmark, recognises link/ref-link/image/footnote-ref/ citation/bracketed-span/inline-footnote/native-span/math forms as ConstructKind::PandocOpaque. This is what keeps emphasis from pairing across these constructs while emission stays on the legacy try_parse_* chain.
• (PLANNED — Phase 1 follow-up) Scoped emphasis passes on strong-matched inner ranges, in build_full_plans for Dialect::Pandoc. The structural shape mirrors the existing CommonMark bracket scoped pass (lines 1247-1306 of inline_ir.rs).

Session recap (RECAP.md)

This skill keeps a rolling recap at .claude/skills/pandoc-ir-migrate/RECAP.md. It is the handoff between sessions — short, judgment-call-only, not a duplicate of the test report.

• At the start of a session: read RECAP.md first. The "Suggested next sub-targets" section is the recommended starting point, and the "Don't redo / known traps" list keeps you from reinventing fixes that already landed (or already failed). If the user named a specific phase or test cluster, prefer that, but still skim the recap so you don't redo prior work.
• At the end of a session: rewrite the Latest session entry in RECAP.md with: phase + sub-target tackled, test count before → after (full workspace), files changed, what not to redo, ranked next sub-targets, and any new traps discovered. Keep it terse — a fresh session should pick up from this entry without scrolling the prior conversation.
• If the session ends with regressions (uncommitted diff is partial), the recap MUST say so explicitly: list the failing tests, classify each into a bucket, and rank the next sub-target by likely shared root cause. Do NOT mark the session "done" if the suite has new red.

Workflow

1. Read RECAP.md for current phase, deferred sub-targets, and trap list. If the user named a sub-target, prefer it; otherwise pick the top-ranked next sub-target from the recap.

2. Establish the test baseline before editing:

   cargo test --workspace --no-fail-fast 2>&1 | grep -E "^test " | grep "FAILED" | sort -u
   

   Save the failing-test set; this is what "no regression" means for this session.

3. Probe the failing inputs. For each input the sub-target touches, capture both the IR's current CST and pandoc-native:

   pandoc <input>.md -f markdown -t native     # primary reference
   pandoc <input>.md -f commonmark -t native   # only if dialect-divergent
   

   For triage across several inputs, drop a throwaway #[ignore]-d probe test into crates/panache-parser/tests/probe_phase1.rs (or similar per-phase name). Template:

   use panache_parser::parse;
   #[test]
   #[ignore = "probe specific inputs"]
   fn probe_targets() {
       for input in [/* failing inputs */] {
           let tree = parse(input, None);
           eprintln!("=== {:?} ===\n{:#?}\n", input, tree);
       }
   }
   

   Run with cargo test -p panache-parser --test probe_phase1 -- --ignored --nocapture. Delete the probe file before finishing the session.

4. Classify each divergence into a failure bucket (see "Failure buckets" above). Apply the pandoc-vs-legacy-fixture trap protocol for any structural diff. TEXT-coalescence diffs are benign — confirm structure, then snapshot-update.

5. Pick the smallest dialect-aware lever that addresses the bucket. Resist adding a new code path when an existing dialect gate already covers the case (just turn the gate on).

6. Apply the change. Validate immediately:

   cargo test -p panache-parser --no-fail-fast
   cargo test --workspace --no-fail-fast
   cargo test -p panache-parser --test commonmark commonmark_allowlist
   

   The conformance allowlist must stay green; CommonMark behavior must not change.

7. Verify net change: same baseline command from step 2.

   • Failures should be a subset of the baseline.
   • If a NEW failure appears (i.e., a previously-green test went red), the change introduced a regression. Revert and try a different lever, OR shrink the change scope. Don't proceed with regressions in the diff.

8. For TEXT-coalescence snapshot updates: regenerate snapshots (find ... -name "*.snap.new" -delete and re-run tests to get fresh .new files), then cargo insta review (or compare .snap vs .snap.new manually) and accept only diffs that are purely TEXT-coalescence. For each: write a one-line note in the recap.

9. Update RECAP.md with the session outcome. If the session ends mid-sub-task with regressions, capture the partial state and rank what's left.

10. Commit only if the diff is clean:

    • All baseline failures gone OR a strict subset.
    • No new failures.
    • clippy and fmt clean.
    • Commit message names the phase + sub-target (e.g. "fix(parser): Phase 1 — add Pandoc opaque math scan"). Otherwise leave the diff uncommitted in the working tree and document the deferral.

Dos and don'ts

• Do read RECAP.md before picking a sub-target.
• Do verify against pandoc-native, not the legacy parser, when a fixture and the new IR disagree.
• Do keep the CommonMark conformance allowlist green every session. If a Pandoc-side change requires touching inline_ir.rs, re-run the allowlist test before declaring done.
• Do record every new trap encountered in RECAP.md so future sessions don't re-walk the same wrong path.
• Don't preserve a legacy-fixture output when it conflicts with pandoc-native. The fixture is the bug.
• Don't treat TEXT-coalescence diffs as regressions. They're improvements; update the snapshot.
• Don't commit a session whose diff has any new red test. Defer instead.
• Don't try the "two-pass + un-remove-between" shortcut for scoped emphasis (see trap above). The state-separation requirement is non-negotiable.
• Don't widen the cascade rule to can_open || can_close (see trap above). It must be &&.
• Don't delete the legacy try_parse_emphasis path before Phase 7. The dispatcher's parse_inline_range_impl still consumes Pandoc bracket constructs through it during Phases 1-6.
• Don't edit conformance report.txt / tests/commonmark/report.json by hand; they're derived. Re-run commonmark_full_report to refresh.

Report-back format

When done, report:

1. Phase + sub-target tackled (e.g. "Phase 1 — scoped emphasis passes for strong-of-emph nesting").
2. Workspace test count before → after (e.g. "13 failing → 4 failing").
3. Files changed, classified by failure bucket.
4. Snapshots updated and the rationale (TEXT-coalescence / structural-change-verified-vs-pandoc-native).
5. Suggested next sub-target ranked by likely shared root cause.
6. Any new trap discovered, captured in RECAP.md.

If the session ends without committing, also report:

7. The exact remaining red tests, classified into buckets.
8. Why they were deferred (which structural change they need).