fix: x-model select sync when model matches no option

[VernSG]

Change-Id: I3b472ed758603a2ef1d0c9a0fa3d6470a92a37cf

Fixes #4885.
When syncing an x-model select whose model value matches no option (such as on dependent selects where the model is null), updateSelect() now preserves any option with the selected attribute (e.g. placeholder bound via :selected or static selected), or falls back to selectedIndex = -1.
This prevents the browser from automatically selecting the first enabled option when the model matches no options, avoiding state desync and dead options.
Added Cypress regression tests for dependent selects and unmatched select values.

Summary by CodeRabbit

• Bug Fixes

  • Improved select controls bound to values that do not match any available option.
  • Preserves disabled placeholders in dependent selects until matching options are available.
  • Clears unmatched single-select values appropriately while retaining explicitly selected fallback options.

• Tests

  • Added coverage for dynamically dependent selects, unmatched model values, placeholders, and subsequent option selection.

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📝 Walkthrough

Walkthrough

updateSelect now preserves an HTML-default selection or clears unmatched single-select elements. Cypress tests cover dependent selects, dynamically generated options, and unmatched model values.

Changes

Select model synchronization

Layer / File(s)	Summary
Update select behavior and validation packages/alpinejs/src/utils/bind.js, tests/cypress/integration/directives/x-model.spec.js	updateSelect tracks matching options and restores the default selection or sets selectedIndex to -1 when no option matches. Cypress tests cover dependent placeholders, generated option selection, and unmatched models.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🔵 Low · up to 6c55c

The PR prevents unmatched model values from selecting the wrong option, but a single-select with multiple selected attributes may still preserve the wrong default option in an edge case. The change is otherwise mergeable with explicit follow-up to select the effective default and add regression coverage.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the primary change: fixing x-model synchronization for selects when the model matches no option.
Linked Issues check	✅ Passed	The implementation preserves an explicitly selected option or sets selectedIndex = -1 when no option matches. The Cypress tests cover dependent selects and unmatched model values. These changes sati…
Out of Scope Changes check	✅ Passed	The changes are limited to updateSelect() and regression tests for the linked select synchronization issue. No unrelated changes are present.

Full details: Linked Issues check

Explanation

The implementation preserves an explicitly selected option or sets selectedIndex = -1 when no option matches. The Cypress tests cover dependent selects and unmatched model values. These changes satisfy issue #4885.

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[calebporzio]

@coderabbitai review

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Actionable comments posted: 1

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Inline comments:
In `@packages/alpinejs/src/utils/bind.js`:
- Line 134: Update the defaultSelectedOption logic in the select binding to use
the last option with a selected attribute, matching HTML behavior when multiple
options are marked selected; add a regression test covering a single select with
multiple selected attributes and no model match.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

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Run ID: ba19a2f6-756e-4d8b-9224-96231025e227

📥 Commits

Reviewing files that changed from the base of the PR and between 022c494 and 6c55ccc.

📒 Files selected for processing (2)

• packages/alpinejs/src/utils/bind.js
• tests/cypress/integration/directives/x-model.spec.js

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

[VernSG]

@coderabbitai review

fixed in the latest commit. updateSelect() now uses .filter().pop() to select the last matching default option, and regression tests have been added.