feat(linter): add useBetterDomTraversing nursery rule by devtechedge · Pull Request #11667 · biomejs/biome

devtechedge · 2026-09-07T21:50:03Z

Nursery port of unicorn/better-dom-traversing.

element.childNodes[0] → .firstChild
element.children[0] → .firstElementChild
element.children[n] (n > 0) suggests .querySelector() (no fix)
chained .parentElement suggests .closest() (no fix)
chained static .querySelector() can be merged (:scope on elements, not on document)
props.children is ignored

Fixes are unsafe: empty collections are undefined vs null, .closest() is not an exact hop count, and a combined selector is not the same as nested querySelector calls. Selectors with a comma or :scope are reported but not rewritten. Comments inside the node block the fix.

Test Plan

cargo test -p biome_js_analyze --test spec_tests nursery::use_better_dom_traversing

3 passed. Specs port the unicorn cases (optional chaining, non-DOM receivers, computed names, JSX props.children).

Docs

Rule docs live in the rule source.

AI disclosure

This PR was written with AI assistance. I reviewed the implementation, tests, and the follow-up review fixes.

Port unicorn/better-dom-traversing. Prefer firstChild, firstElementChild, closest, and merged querySelector calls over positional DOM walks. Closes #11641

agentscanapp · 2026-09-07T21:50:07Z

A maintainer will take a look as soon as they can. In the meantime, please make sure that:

the description follows our PR template
any related issues are linked
existing tests still pass

changeset-bot · 2026-09-07T21:50:07Z

🦋 Changeset detected

Latest commit: 71f4e9d

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

This PR includes changesets to release 13 packages

Name	Type
@biomejs/biome	Patch
@biomejs/cli-darwin-arm64	Patch
@biomejs/cli-darwin-x64	Patch
@biomejs/cli-linux-arm64-musl	Patch
@biomejs/cli-linux-arm64	Patch
@biomejs/cli-linux-x64-musl	Patch
@biomejs/cli-linux-x64	Patch
@biomejs/cli-win32-arm64	Patch
@biomejs/cli-win32-x64	Patch
@biomejs/wasm-bundler	Patch
@biomejs/wasm-nodejs	Patch
@biomejs/wasm-web	Patch
@biomejs/backend-jsonrpc	Patch

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Walkthrough

Adds the nursery useBetterDomTraversing rule. It reports indexed DOM collections, repeated parentElement access, and mergeable querySelector chains. It provides guarded unsafe fixes for first-child access and static selector merging. The change registers rule options, adds a Changesets patch entry, and includes JavaScript and JSX fixtures for valid and invalid patterns.

Suggested reviewers: biome-cookie, dyc3

Merge Risk: 🔵 Low · up to da553

The new DOM-traversal rule is ready functionally, but its changeset still lacks required issue and assist links, reducing release-note traceability. Add the links before merging.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the addition of the `useBetterDomTraversing` nursery rule and matches the main change.
Description check	✅ Passed	The description accurately summarises the rule port, suggested transformations, unsafe-fix limits, tests, and linked issue.
Linked Issues check	✅ Passed	The implementation fulfils issue `#11641` by adding the proposed `useBetterDomTraversing` nursery rule, configuration, diagnostics, fixes, and test coverage for the ported behaviours.
Out of Scope Changes check	✅ Passed	The changeset, rule options, implementation, and test fixtures directly support the linked rule-port objective. No unrelated code changes are evident.

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Actionable comments posted: 2

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Inline comments:
In @.changeset/better-dom-traversing.md:
- Line 5: Add the required issue and assist links to the changeset entry for
useBetterDomTraversing, preserving the existing rule link and description.
Ensure the release note includes all repository-required link types: issue,
rule, and assist.

In `@crates/biome_js_analyze/src/lint/nursery/use_better_dom_traversing.rs`:
- Line 322: Update the selector guard in the relevant lint logic to detect
“:scope” case-insensitively, preventing uppercase or mixed-case variants from
setting can_fix to true; add the “:SCOPE > .item” case to the existing fixture.

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.changeset/better-dom-traversing.md
crates/biome_js_analyze/src/lint/nursery/use_better_dom_traversing.rs
crates/biome_js_analyze/tests/specs/nursery/useBetterDomTraversing/invalid.js
crates/biome_js_analyze/tests/specs/nursery/useBetterDomTraversing/valid.js
crates/biome_js_analyze/tests/specs/nursery/useBetterDomTraversing/valid.jsx
crates/biome_rule_options/src/lib.rs
crates/biome_rule_options/src/use_better_dom_traversing.rs

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dyc3 · 2026-09-07T22:57:37Z

also, this is missing the AI disclosure

codspeed · 2026-09-07T23:06:09Z

Merging this PR will not alter performance

✅ 74 untouched benchmarks
⏩ 270 skipped benchmarks¹

_{Comparing devtechedge:feat/use-better-dom-traversing (71f4e9d) with main (e7b3b95)}

270 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. ↩

Rewrite diagnostics to what/why/how, build the querySelector merge only in action(), walk optional chains with ancestors(), and treat :scope as ASCII case-insensitive.

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Actionable comments posted: 1

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Inline comments:
In `@crates/biome_js_analyze/src/lint/nursery/use_better_dom_traversing.rs`:
- Line 323: Update the selector validation in the rule around the existing
literal :scope check to reject selectors containing CSS escapes before offering
the merge fix, and preserve the current behavior for valid selectors. Add an
unsafe-fix regression fixture covering the escaped :scope spelling such as :\73
cope.

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devtechedge · 2026-09-07T23:34:55Z

Thanks. Pushed a follow-up for the diagnostic wording, deferred merge fix, ancestors(), changeset, and the :scope case. AI disclosure is now in the PR body.

:\73 cope is :scope. Do not auto-merge those.

dyc3 · 2026-09-07T23:58:35Z

@biome-cookie review

biome-cookie

Review Summary

Review complete. 4 findings were added inline.

Questions

is_nested_indexed_children suppresses the inner diagnostic only when the surrounding member is .children. Should the same suppression apply to nested .childNodes[0] accesses, or is it intentional that they produce multiple diagnostics?
The querySelector merge fix replaces inner_object with root, which is a direct descendant of the node being replaced. Has this overlapping replacement been verified as robust across larger mutation batches, and would it be cleaner to clone or rebuild root before insertion?

Review Status

Scope: Adds nursery rule useBetterDomTraversing with rule logic, tests/snapshots, and generated configuration/migration entries.
Branch target: main
Changeset: .changeset/better-dom-traversing.md
Brief: Port eslint-plugin-unicorn/better-dom-traversing to a new nursery rule
Validation: Static review only; no project code was run.
Fetch: e7b3b95...e120885

Skip the inner diagnostic on childNodes[0].childNodes[0]. Clone the querySelector receiver before replacing so the fix does not move a subtree out of itself.

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In `@crates/biome_js_analyze/src/lint/nursery/use_better_dom_traversing.rs`:
- Around line 428-431: Update the nested childNodes suppression logic around the
token-name check so numeric outer indices suppress the inner access only when
the outer index is 0; preserve diagnostics for inner childNodes accesses when
the unsupported outer index is nonzero. Add the
`element.childNodes[0].childNodes[1]` coverage case to `invalid.js`.

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element.childNodes[0].childNodes[1] produced no diagnostic because nested childNodes suppression treated any numeric outer index as a hit. Only suppress the inner access when the outer access is also childNodes[0].

dyc3

please feel free to hit "resolve" on review comments you have addressed

Element.querySelector combined selectors are prefixed with :scope so the rewrite stays descendant-relative, matching chained calls. document.querySelector does not need that. Selector chains use SmallVec; optional-chain checks go through AnyJsExpression.

devtechedge · 2026-09-08T12:28:26Z

:scope is “this element” - the node you called .querySelector() on.

The prefix preserves the chain. element.querySelector("a b") can match a b whose a ancestor is element itself. Chained .querySelector() never does that. :scope a b stays descendant-relative. document.querySelector already starts at the document, so that rewrite is just "a b".

Also in this push: SmallVec<[String; 4]> for the selector list, and AnyJsExpression::is_optional_chain in the syntax crate.

Resolved the earlier threads from this side once GitHub lets me - please hit resolve on anything still open that this covers.

dyc3 · 2026-09-08T12:51:56Z

does github really not show you the resolve button? you should be able to see it since its your PR

devtechedge · 2026-09-08T13:18:04Z

You're right - it's there, I just missed it on my phone.

Thanks for the nudge! I went through and resolved the threads that are done.

One cookie comment I left open on purpose (storing the merged selector in state), because that would build the fix in run() and you asked to only build it in action().

devtechedge · 2026-09-08T17:16:06Z

Thank you for the careful review, and for merging this.

The notes on diagnostics, :scope, SmallVec, and moving is_optional_chain into the syntax crate were really helpful.

I learned a lot from the pass. Grateful you took the time for my first-time contribution here!

@html

@html

feat(linter): add useBetterDomTraversing nursery rule

af0c277

Port unicorn/better-dom-traversing. Prefer firstChild, firstElementChild, closest, and merged querySelector calls over positional DOM walks. Closes #11641

agentscanapp Bot added the agentscan:automation-signals label Sep 7, 2026

github-actions Bot added A-CLI Area: CLI A-Project Area: project A-Linter Area: linter L-JavaScript Language: JavaScript and super languages A-Diagnostic Area: diagnostocis labels Sep 7, 2026

devtechedge added a commit to devtechedge/oss-contributions that referenced this pull request Sep 7, 2026

Ledger biomejs/biome#11667 useBetterDomTraversing nursery rule

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Comment thread .changeset/better-dom-traversing.md Resolved

Comment thread crates/biome_js_analyze/src/lint/nursery/use_better_dom_traversing.rs Resolved

dyc3 reviewed Sep 7, 2026

View reviewed changes

feat(linter): address useBetterDomTraversing review

cbb50de

Rewrite diagnostics to what/why/how, build the querySelector merge only in action(), walk optional chains with ancestors(), and treat :scope as ASCII case-insensitive.

coderabbitai Bot reviewed Sep 7, 2026

View reviewed changes

Comment thread crates/biome_js_analyze/src/lint/nursery/use_better_dom_traversing.rs Resolved

fix(linter): skip querySelector merge when selectors contain CSS escapes

e120885

:\73 cope is :scope. Do not auto-merge those.

biome-cookie reviewed Sep 8, 2026

View reviewed changes

fix(linter): clone merge root and suppress nested childNodes

91b18e3

Skip the inner diagnostic on childNodes[0].childNodes[0]. Clone the querySelector receiver before replacing so the fix does not move a subtree out of itself.

coderabbitai Bot reviewed Sep 8, 2026

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Comment thread crates/biome_js_analyze/src/lint/nursery/use_better_dom_traversing.rs Resolved

fix(linter): report inner childNodes[0] when outer index is not 0

da553eb

element.childNodes[0].childNodes[1] produced no diagnostic because nested childNodes suppression treated any numeric outer index as a hit. Only suppress the inner access when the outer access is also childNodes[0].

dyc3 reviewed Sep 8, 2026

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github-actions Bot added the A-Parser Area: parser label Sep 8, 2026

dyc3 approved these changes Sep 8, 2026

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Comment thread crates/biome_js_analyze/src/lint/nursery/use_better_dom_traversing.rs Resolved

fix(linter): avoid allocating collection name in nested index check

71f4e9d

dyc3 merged commit e997900 into biomejs:main Sep 8, 2026
36 checks passed

github-actions Bot mentioned this pull request Sep 8, 2026

ci: release #11614

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docs: record biomejs/biome#11667 as first upstream merge

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Ledger biomejs/biome#11667 useBetterDomTraversing nursery rule

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devtechedge added a commit to devtechedge/oss-contributions that referenced this pull request Sep 12, 2026

docs: record biomejs/biome#11667 as first upstream merge

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