fix: don't match anything for empty ~= attribute value

[NevanDeCoteau]

Fixes #1910

Per the CSS spec, [a~=""] matches nothing. css-select matched elements with an empty value and values with leading, trailing or doubled spaces, because an empty value produced a regex that matches the empty string.

This change makes the ~= rule return falseFunc for an empty value, the same way it already does for values containing whitespace.

Tests added to test/attributes.ts:

[foo~=''] compiles to falseFunc
[a~=""] matches none of the four elements from the issue
[a~="x"] still matches whole words

I confirmed the new tests fail without the fix. The full test suite and lint pass locally.

Summary by CodeRabbit

• Bug Fixes
  • Attribute selectors using ~= with an empty value now correctly match no elements. Existing selectors with non-empty values continue to work.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-13T18:52:25.444416Z	582097c	PR opened

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: ASSERTIVE
• Plan: Advanced
• Run ID: b3e28bbf-95b3-4eae-9e0d-7c19d46b06d1

📥 Commits

Reviewing files that changed from the base of the PR and between dbb1879 and 582097c.

📒 Files selected for processing: 2

• src/attributes.ts
• test/attributes.ts

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📝 Walkthrough

The ~= attribute selector now returns a non-matching function when its value is empty or contains whitespace. Tests cover the compiled matcher and DOM selection for empty and non-empty values.

Changes: Empty ~= Matching

Layer / File(s)	Summary
Reject empty ~= values src/attributes.ts, test/attributes.ts	The selector rejects empty values as well as values containing whitespace. Tests verify that an empty value matches no elements and that x matches three elements.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 58209

The empty ~= selector now matches no elements, while non-empty whole-word matching remains covered. No actionable merge risk is identified.

Pre-merge checks: 5

Passed checks: 5 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: preventing matches for empty ~= attribute values.
Linked Issues check		The PR satisfies issue #1910. src/attributes.ts now returns boolbase.falseFunc when the ~= value is empty or contains whitespace. Tests verify compilation to falseFunc, zero matches for the fo…
Out of Scope Changes check		The changes stay within issue #1910. The source change implements the empty-value rule, and the added tests cover the required regression and preserve existing whole-word behavior. No unrelated change…
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…

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_{A rabbit checked the selector with care,
An empty value found no match there.
Whitespace still gets turned away,
While x finds three along the way.
Then off hopped the rabbit, pleased with the day.}

_{Comment @coderabbitai help to get the list of available commands.}

[cubic-dev-ai]

No issues found across 2 files

_{View guided diff | Re-trigger cubic}

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; empty ~= operands now match nothing, while nonempty matching remains unchanged.

Summary

Makes [a~=""] match nothing by returning boolbase.falseFunc before building the word-matching regex.

• Empty ~= values match no elements.

No actionable issues found. Tests were inspected but not run.

_{Reviews (1) · Last reviewed commit: "fix: don't match anything for empty ~= v..." · Reviewed by Greptile}