[lxsmnsyc]

DOM output no longer declares positional walks to nodes that nothing reads. These walks shipped as bare property reads such as _el$2.firstChild;, because a minifier keeps a read that could be a getter.

Changes

• prune_unused_walks in packages/compiler/src/dom/element.rs drops a var x = y.firstChild or y.nextSibling declaration when no later statement reads x.
• It runs from the last declaration back, so a walk that only feeds a dropped walk is dropped too.
• The statements it checks are the inserts, attribute setters and the batched effect of the same template root.
• pruneUnusedWalks in packages/babel-plugin/src/dom/template.ts does the same, so both compilers emit equal output.
• 23 Babel and 15 compiler DOM fixture snapshots lose their unused walks.

Example, <h1>User : {name()}</h1>:

// before
var _el$ = _tmpl$(), _el$2 = _el$.firstChild;
_$insert(_el$, name, null);
// after
var _el$ = _tmpl$();
_$insert(_el$, name, null);

Proof

• packages/compiler: cargo test, cargo clippy -- -D warnings and vitest run pass (6880 tests), including Babel parity.
• packages/babel-plugin: pnpm test passes (414 tests).
• packages/web: client, server and hydration suites pass (1556, 1905 and 712 tests). These compile through the Babel plugin, so they run the pruned output.

Cost

Client gzip of the Vite builds of the repo's 13 examples, against the same base:

Example	Change
effect	-24 B
canvas	-10 B
todos	-10 B
hackernews-spa	-6 B
notes	-4 B
other 8	0 B

• Hydrating builds do not change.
• Server builds change by 1 to 3 B from gzip noise. The SSR transform is not touched.
• The measurements come from solid-optimizer (debates/v0.5.0/evidence/unused-walks-solid-examples.txt). Its own examples show -7 to -43 B.
• Compile time adds one identifier visit over each template root's statements.

Risk

• A walk is dropped only when it is a plain firstChild or nextSibling read. No later statement of the same template root may read its name. A wrong drop would show up as a ReferenceError in the web suites, and none happened.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: e938536

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

This PR includes changesets to release 15 packages

Name	Type
@solidjs/compiler	Patch
@solidjs/babel-plugin	Patch
test-integration	Patch
@solidjs/diagnostics	Patch
@solidjs/element	Patch
@solidjs/h	Patch
@solidjs/html	Patch
@solidjs/signals	Patch
solid-js	Patch
@solidjs/universal	Patch
@solidjs/web	Patch
board-example	Patch
canvas-example	Patch
server-dbmon-example	Patch
todos-server-example	Patch

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[codspeed]

Merging this PR will not alter performance

1 warning

⚠️ 1 benchmark is dominated by system calls

System calls cannot be simulated consistently and are left out of the measure. The reported value understates the real cost. Switch to the Walltime instrument to measure them.

Learn more about system calls

See affected benchmarks

✅ 201 untouched benchmarks
⏩ 5 skipped benchmarks¹

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_{Comparing lxsmnsyc:perf/drop-unused-dom-walks (e938536) with next (8138dab)}

Footnotes

1. 5 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. ↩