fix(web): move delegated event handlers off the Solid 1 $$<type> key

[ryansolid]

Problem

Solid 1 delegates from document and fires any $$click / $$input / … it finds while walking up from the target. Solid 2 delegates from the render root but stamped the same $$<type> key on elements. So on any page with both:

• a 1.x runtime (an older embedded widget, a devtools panel built on 1.x — both a 1.x custom element beside a 2.x app and TanStack devtools inside a 2.x app were reported on Discord) re-fires every delegated handler in the 2.x app, and
• a 2.x root fires 1.x handlers rendered inside it, which 1.x's document listener then fires again.

1.x's eventHandler consults nothing on the event object besides cancelBubble (and its own hydration replay buffer while hydrating), so no "already handled" mark can stop it. Scoping our listener to the root only controls what our walker sees. The only lever that works against a runtime we can't change is a key it doesn't look for.

Change

Compiled output (@solidjs/babel-plugin, @solidjs/compiler) and the runtime (addEvent, eventHandler) now stamp _$$<type> / _$$<type>Data. Emit shape is unchanged — _el$._$$click = handler — so there is no per-element cost.

_$ is the existing Solid-owned expando family (_$host, _$owner, _$classes, _$styles, _$multiple). The extra $ gives event keys their own namespace so a user-configured custom delegated event (delegatedEvents: ["host"]) can never collide with one of those.

Wire contract

The key, the _$SOLID_EVENT_OWNER mark, and the walk rules are now documented at the top of client.ts as the delegated-event wire contract. It is read off the DOM and the event by whichever Solid copy is listening, so it is shared between every copy on a page — two bundles of the same major nested in each other, or a future major nested in this one — and is frozen going forward. Changing any of it means a new key prefix, not a new shape under the old one. (Prior art: Svelte hit exactly this within 5.x when a minor changed the shape of __click — sveltejs/svelte#17057.)

Tests

packages/web/test/delegated-event-cross-runtime.spec.tsx:

• carries a faithful copy of the 1.x walker attached to document beside a 2.x root — light DOM, open shadow root (the reported custom-element setup), and 1.x content nested inside a 2.x root — asserting single dispatch in each direction. All four fail on the old key (verified by flipping the runtime and compiler back and rebuilding).
• loads client.ts twice as separate module instances (?copy=2) and nests a root from one inside the other: single dispatch, inner→outer ordering, stopPropagation across instances, outer handlers above the inner root still fire. This pins the same-major-twice case and doubles as the freeze test for the contract.

Full suites pass: compiler (Rust + 5785 fixture cases), Babel plugin, web under both native and Babel JSX (client/server/hydrate), test-types, h, html, element.

Migration

Anything reading el.$$click directly must switch to el._$$click.

Workarounds no longer needed

Closed shadow roots, delegateEvents: false, and root.addEventListener(type, e => e.stopPropagation()) all worked around this from the app side; after this change none are required for 1.x interop.

[changeset-bot]

🦋 Changeset detected

Latest commit: 6d2bdeb

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

This PR includes changesets to release 11 packages

Name	Type
@solidjs/web	Patch
@solidjs/babel-plugin	Patch
@solidjs/compiler	Patch
@solidjs/element	Patch
@solidjs/h	Patch
@solidjs/html	Patch
test-integration	Patch
@solidjs/diagnostics	Patch
@solidjs/signals	Patch
solid-js	Patch
@solidjs/universal	Patch

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[codspeed]

Merging this PR will not alter performance

✅ 172 untouched benchmarks
⏩ 3 skipped benchmarks¹

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_{Comparing fix/delegated-event-key (6d2bdeb) with next (7624320)}

Footnotes

1. 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. ↩

[coveralls]

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Coverage Stats

Relevant Lines:	1035
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