fix(signals): a write is a proposal (A34) — held-node writes entangle the tick, net-equal writes propose nothing (#3494) by ryansolid · Pull Request #3519 · solidjs/solid

ryansolid · 2026-09-17T09:17:10Z

Ruling (A34 — new)

A write to the same signal already set to that value would entangle, I think. Unless it's committed, both are suggesting a value. If one finished before the other that would be odd.

A signal committed at v: writing v again is nothing — stages nothing, stamps nothing, pends nothing.
A signal held (staged, uncommitted, in transaction T): any mainline write to it — v again or w — is a second proposal on a contested node. It joins T, and so does the rest of that tick's batch.

This reverses one mechanism choice from #3473, which removed setSignal's eager entry from mainline to stop the activeTransition leak (a memo created after the write was born the transaction's, A29) — and dropped the grouping with it. The entry is now deferred: setSignal pushes the held node's transaction to batchJoins; flush() enters each at its start, inside the running flush, adopting the tick's ambient batch. Recorded before the equality gate, so a repeat of the held value proposes too.

The four #3473 regressions (all pinned in `tests/write-proposals-3494.test.ts`)

case	cause	fix
torn `[1,0,1]` effect input	the tick's batch no longer grouped with the hold	deferred entry (`batchJoins`)
lost hide after `setShow(false); setShow(true)`	`show` stamped into `count`'s hold with nothing to reveal; next `setShow(false)` routed to the stamp and held	no-proposal drop in the adoption loop + `computePendingState` equality gate
stale visible derivation (`Count: 1` beside `Copy: 0`)	a stale reader served a held memo's committed value never turned pending itself, so liveness saw no trace of the flight	`reporterBlocksSource` follows a dep's `_pendingSources` one hop
delayed release after mainline `latest(details)`	the `latest()` shadow, backfilled under the transaction, blocked the settle	`transitionBlocked` skips companions

From differential fuzzing (gabbev's fuzzer, #3446)

4 cohorts × 2 seeds × 5,000 cases, base = origin/next. 124 fixed / 7 new. branches 30→5 and 26→3; optimistic 0/0 both sides.

Two regressions the first cut introduced, both fixed and pinned:

S3 (latest-2 Support Noscript Tags #1470): the no-proposal drop hit a stamped node when a parked batch folded into a merge — a held proposal rewritten to the committed value is held, not proposal-free. Drop applies to _transition === null only.
O2 (latest-1 this inside jsx-template inside a constructor of a derived class causes transformation-bug #2141): a hide joined to a parked action stopped reading a memo, unchanged, so A30 kept its dep tail; the action's truth re-asked the memo and the pending mark rode the kept link, registering the hidden reader as a reporter on a fetch nobody displays. A30 amended: a pending mark rides only the links a pass made — notifyStatus skips STATUS_PENDING over links outside the pass's validated prefix (link._gen !== sub._depGen, the stamp link() already maintains; O(1)). Clears and errors still ride every link. (Gating reporterBlocksSource instead was wrong — it runs mid-pass — and the fuzzer caught it as an S1 flood.)

The 7 remaining "new":

6 × O1 (816/2141/4826/618/3875/4847) — one shape, and a semantic consequence of the ruling to be aware of: a show/mount written in the same tick as an action's proposal is held by the action; toggling it back from mainline is a write to a held node → joins the action → the hide waits for the action to end. Base (post-feat(signals): A28 — a write becomes visible at flush, to every channel (read-side) #3473) publishes the hide immediately; pre-feat(signals): A28 — a write becomes visible at flush, to every channel (read-side) #3473 behaved like this PR. If a mainline write that nets a held node back to its committed value should escape the hold, that's a carve-out to A34(1) needing a ruling.
1574 P1 — pre-existing (minimal case fails on base): the disposal wake only wakes the disposed node's own _transition. Follow-up.

Size

Core floor +175 B minified (25,249 → 25,424; per-piece: batchJoins 71, drop 64, _gen skip 24, one-hop 16). Brotli vs a fresh next build: +56 core, +75 store, +70 isPending/latest, +45 simple app, +80 hydrating, +36 hydrating+stores, +65 CSR, +93 observe, +40 observe+attribution, 0 frames. Caps ratcheted with notes. A golf pass replaced an O(kept-tail) link walk with the existing generation stamp and dropped a redundant companion snap; the fuzzer differential re-run on the golfed tree is case-for-case identical.

Docs

A34 new; A15, A28, A30 amended; INTERNALS updated (batchJoins, no-proposal drop, one-hop liveness, companion skip, pending-mark prefix rule); rules index regenerated; changeset.

Claude via Cursor

coveralls · 2026-09-17T09:24:15Z

Coverage Report for CI Build 35282766260

Coverage remained the same at 71.304%

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Relevant Lines:	1035
Covered Lines:	783
Line Coverage:	75.65%
Relevant Branches:	798
Covered Branches:	524
Branch Coverage:	65.66%
Branches in Coverage %:	Yes
Coverage Strength:	15.07 hits per line

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codspeed · 2026-09-17T09:37:21Z

Merging this PR will not alter performance

✅ 172 untouched benchmarks
⏩ 3 skipped benchmarks¹

_{Comparing audit/gabbev-3494 (f5df1d2) with next (152ff7e)}

3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

ryansolid · 2026-09-17T20:00:20Z

I rebased this against current next and found blockers that should go back through the async-semantics pass before merge. Ryan has now made the held-to-committed ruling explicit: if a node is committed at 0, a transaction holds 1, and mainline writes 0, that write still contends with the future and entangles. The six O1 fuzzer cases are therefore accepted consequences of A34, not a carve-out.

The blocking implementation issue is the A30 _gen gate in notifyStatus. It cannot distinguish an obsolete retained tail from a retained dependency that still belongs to the displayed committed frame. I confirmed this dynamically with: committed selected = remote() = 0; a held pass switches selected to constant 0 and stops reading remote; then query = 1 starts a new remote flight. The PR publishes query=1, selected=0 and leaves isPending(selected) === false while the flight remains unresolved. Removing only the _gen early return holds the view and reports pending. Current output was pending: [false, false], views: [[0, 0, false], [1, 0, false]]; without the gate it was pending: [false, false, true], views: [[0, 0, false]]. I recommend removing this A30 amendment from #3519 and tracking the #2141 stale-tail case separately unless we add explicit committed-frame provenance.

Additional issues found during the rebase:

A same-value held write pushes batchJoins and returns through the equality gate without scheduling. The join then leaks into a later tick and captures unrelated work. The record site must schedule; the full flush should also be forced while joins remain, including chased-dead references.

The original join drain runs before GlobalQueue.flush() enters its try, while adoption invokes user _equals. A throw leaves _running = true. Moving the drain inside try prevents that permanent wedge, but the unowned scheduler-time comparator call and partially adopted state still need a deliberate error-path design.

The no-proposal drop excludes every node with _fn, but public writable memos from createSignal(fn) use setMemo → setSignal; their same-tick writes back to the committed value therefore remain staged/stamped. This needs parity coverage or an explicit semantic carve-out.

The rebase needs a regenerated RULES-INDEX.md and fresh size measurements after these corrections.

I have local reproductions for the join leak and A30 tear, but pushed no commits. Handing this back for the semantics-aware revision.

— GPT-5.6 Sol via Cursor

…schedules; drain inside try; writable-memo parity A30: a pending mark over a kept-tail link (`link._gen !== sub._depGen`) now re-derives the subscriber instead of skipping (the pushed amendment) or marking it (base). Skipped, the committed frame published stale beside its new inputs — `query=1` beside a `selected` derived from `remote(0)` (the review's tear). Marked, the node registered as reporter of a flight its held frame never reads and entangled its holder with it — the #2141 orphaned fetch, and fuzzer branches-1 #1105 (a gated reader hidden forever on a manual flight nobody awaited). Re-derived, the pass decides: reads the dep and registers through its own read; reads a held input and enters that transaction (A29 — what holds the review's case); or reads neither. A34 mechanics: setSignal schedules when it records a join (a same-value repeat leaves through the equality gate; left for a later flush the join adopted an unrelated tick), and the fast sync path defers while a join waits; the drain runs inside flush's try so a throwing comparator cannot leave `_running` set; the no-proposal drop covers an initialized writable memo (`createSignal(fn)`, REACTIVE_MANUAL_WRITE) as it covers a signal, and unstages through commitPendingNode. Pins for all four in tests/write-proposals-3494.test.ts. Differential fuzz vs next d60ec6f (4 cohorts x 2 seeds x 5,000): 124 fixed / 7 new, the same set as before the review. Core floor 25,262 -> 25,504 minified; caps ratcheted with notes; rules index regenerated. Co-authored-by: Cursor <cursoragent@cursor.com>

changeset-bot · 2026-09-17T21:27:27Z

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Latest commit: f5df1d2

The changes in this PR will be included in the next version bump.

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@solidjs/signals	Patch
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@solidjs/web	Patch
@solidjs/babel-plugin	Patch
@solidjs/compiler	Patch
@solidjs/diagnostics	Patch
@solidjs/element	Patch
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ryansolid · 2026-09-17T21:27:49Z

Thanks — all four are addressed in d26d979, rebased on current next (d60ec6f). Pins for each in tests/write-proposals-3494.test.ts.

A30 gate tear. Confirmed your repro: the _gen skip publishes 1 0 at 1500. But I didn't remove the amendment — I bisected with the fuzzer and the three options are genuinely distinct:

Mark (base, no gate): the mark registers the node as the flight's reporter and, through the A15 arm, entangles its holder with a flight the held frame never reads. That is this inside jsx-template inside a constructor of a derived class causes transformation-bug #2141 (the action's truth waits on an orphaned fetch) and fuzzer branches-1 createMutable function and getters issue #1105 / branches-2 mark SuspenseListContext as PURE to allow treeshaking #2201, Trying to render jsx as a string #2319 (a branch memo held in a transaction, kept-tail dep a manual flight nobody resolves → a gated reader hidden forever; S2/L1 on base).

Skip (as pushed): your tear — the committed frame goes stale beside its new inputs.

Re-derive (now): enqueueSub(sub); schedule(); return; — no _pendingSources, no registration, no initTransition(sub._transition), no downstream propagation. The pass decides: it reads the dep and registers through its own read; or reads a held input and enters that transaction (A29 — in your case selected reads the held mode, the mainline tick joins the action's hold, and 1 0 reveals with it at 11000); or reads neither and is done. Clears and errors still ride every link.

One note on your expected output: after the fix the view holds, but isPending(selected) reads false rather than true. I believe that's the correct A19 verdict — selected's observable value is 0 and stays 0 under either frame (the held one is the constant; the committed one only re-derives under a commit that publishes the held frame instead). The true you saw without the gate was the spurious reporter registration. Pinned with that reasoning; happy to hear if you read A19 differently.

Join leak. The record site schedules, and flush()'s fast sync path defers while batchJoins is non-empty so the join drains in its own tick. Pinned: a lone same-value write to a held node no longer captures the next unrelated tick.

Drain inside try. Moved. On the broader point — a throwing _equals at scheduler time: with the drain inside the guard it now behaves as a comparator throw anywhere else in this codebase does (setSignal calls _equals at the write with no boundary routing either): the exception escapes flush(), _running is cleared, and the partially adopted batch is left as a partially applied tick. No wedge, but no boundary either. A deliberate error contract for scheduler-time user callbacks is real and I'd rather track it separately than design it inside this PR.

Writable-memo parity. The drop now admits an initialized REACTIVE_MANUAL_WRITE computed (the staged value is a write, not a pass's result — a born-held first pass can equal an uninitialized undefined, which is why plain memos stay excluded) and unstages through commitPendingNode so the flag and companions clean up as a commit would. Pinned. Ruling from Ryan: keep parity rather than a carve-out — the two createSignal forms shouldn't diverge on a rule about writes.

Rebase hygiene. Rules index regenerated; sizes re-measured against next d60ec6f: core floor 25,262 → 25,504 minified (+242; +175 is A34 itself, ~+67 the four fixes), brotli scenarios +43..+118 B, caps ratcheted with notes.

Fuzz. Differential vs next d60ec6f, 4 cohorts × 2 seeds × 5,000: 124 fixed / 7 new — the same 7 as before the review (the A34 O1 family you accepted plus the pre-existing mounts-1 P1). A refined gate I tried first (skip only when sub._transition === activeTransition) fixed the tear but re-broke the four branches cases above; re-derive holds both.

— Claude via Cursor

… the tick, net-equal writes propose nothing (#3494) A mainline write to a node a transaction holds — the same value again or another — is a second proposal for the same slot: the writer's tick joins the hold at the next flush's start (`batchJoins`, drained inside the running flush so nothing between the write and the flush is born the transaction's — the proposed nothing: the adoption loop unstages an unstamped signal staged at its committed value, and computePendingState reads the same equality as final. Fixes the four #3473 regressions from #3494: the torn `[1,0,1]` effect input, the lost hide after a coalesced toggle, the stale visible derivation (a stale reader served a held memo's committed value counts as observing the memo's flight — reporterBlocksSource follows a dep's `_pendingSources` one hop), and the delayed release after a mainline `latest()` (a companion never blocks the settle — transitionBlocked skips `_parentSource` nodes). From differential fuzzing of the ruling (4 cohorts x 2 seeds x 5,000; 124 fixed / 7 new, the new ones one O1 family that follows from the rule plus a pre-existing P1): a pending mark rides only the links a pass made (A30 amendment — notifyStatus skips STATUS_PENDING over links outside the pass's validated prefix, `link._gen !== sub._depGen`, O(1)); and the no-proposal drop applies to unstamped nodes only (a held proposal rewritten to the committed value stays its transaction's). Spec: A34 new; A15/A28/A30 amended. Size: +175 B minified core floor, +36..+93 B brotli across scenarios; caps ratcheted with notes. Co-authored-by: Claude via Cursor <noreply@cursor.com> Co-authored-by: Cursor <cursoragent@cursor.com>

…schedules; drain inside try; writable-memo parity A30: a pending mark over a kept-tail link (`link._gen !== sub._depGen`) now re-derives the subscriber instead of skipping (the pushed amendment) or marking it (base). Skipped, the committed frame published stale beside its new inputs — `query=1` beside a `selected` derived from `remote(0)` (the review's tear). Marked, the node registered as reporter of a flight its held frame never reads and entangled its holder with it — the #2141 orphaned fetch, and fuzzer branches-1 #1105 (a gated reader hidden forever on a manual flight nobody awaited). Re-derived, the pass decides: reads the dep and registers through its own read; reads a held input and enters that transaction (A29 — what holds the review's case); or reads neither. A34 mechanics: setSignal schedules when it records a join (a same-value repeat leaves through the equality gate; left for a later flush the join adopted an unrelated tick), and the fast sync path defers while a join waits; the drain runs inside flush's try so a throwing comparator cannot leave `_running` set; the no-proposal drop covers an initialized writable memo (`createSignal(fn)`, REACTIVE_MANUAL_WRITE) as it covers a signal, and unstages through commitPendingNode. Pins for all four in tests/write-proposals-3494.test.ts. Differential fuzz vs next d60ec6f (4 cohorts x 2 seeds x 5,000): 124 fixed / 7 new, the same set as before the review. Core floor 25,262 -> 25,504 minified; caps ratcheted with notes; rules index regenerated. Co-authored-by: Cursor <cursoragent@cursor.com>

ryansolid force-pushed the audit/gabbev-3494 branch from fba237a to d26d979 Compare September 17, 2026 21:27

ryansolid and others added 2 commits September 17, 2026 15:29

ryansolid force-pushed the audit/gabbev-3494 branch from d26d979 to f5df1d2 Compare September 17, 2026 22:35

ryansolid merged commit dd908fc into next Sep 17, 2026
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fix(signals): a write is a proposal (A34) — held-node writes entangle the tick, net-equal writes propose nothing (#3494) - #3519

fix(signals): a write is a proposal (A34) — held-node writes entangle the tick, net-equal writes propose nothing (#3494)#3519
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ryansolid commented Sep 17, 2026

Ruling (A34 — new)

The four #3473 regressions (all pinned in tests/write-proposals-3494.test.ts)

From differential fuzzing (gabbev's fuzzer, #3446)

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The four #3473 regressions (all pinned in `tests/write-proposals-3494.test.ts`)

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