fix: add normalization for repeatable parameters

[rastuhacode]

🔗 Linked issue

Resolves #4135

📚 Description

With trailingSlash: true, route localiztion creates:

/:slug(.*)*/
/fr/:slug(.*)*/

Vue Router parses it like:

// Url: .../test/
{ slug: ['test', ''] }

Then switchLocalePath() copies those params into the localized named route. Vue Router joins the array as test/, then the localized route pattern adds its configured slash, so basically happens:

/fr/ + test/ + / = /fr/test//

Navigating there produces another empty parameter element, so the process repeats indefinitely.
The malformed SEO URLs are a downstream symptom: locale head generation calls switchLocalePath() for canonical and alternate URLs.

Solution

• Added normalization process for repeatable params (normalizeRepeatableParams), which removes only trailing empty elements from repeatable route params before named-route resolution.
• Added regression tests

Summary by CodeRabbit

• Bug Fixes
  • Improved localized route handling for repeatable and catch-all parameters.
  • Preserved interior empty path segments while removing unnecessary trailing segments.
  • Ensured locale switching and route resolution produce consistent URLs.
  • Corrected canonical localized URLs to use exactly one trailing slash where applicable.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 7fffa2c8-0df5-474d-8157-d7e536104542

📥 Commits

Reviewing files that changed from the base of the PR and between 6a72568 and 274f2ac.

📒 Files selected for processing (2)

• src/runtime/routing/routing.ts
• test/routing-head.test.ts

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Walkthrough

The routing implementation adds normalization for repeatable route parameters. It removes trailing empty array elements and preserves interior empty elements before named localized route resolution. The routing tests add configurable route records and trailing-slash behavior, then cover catch-all routes, locale switching, URL queries and hashes, route consistency, and canonical trailing-slash URLs.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 274f2

The change normalizes trailing empty repeatable route parameters to prevent duplicate slashes in localized URLs; no actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 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: normalization for repeatable route parameters.
Linked Issues check	✅ Passed	The implementation and regression tests address duplicate trailing slashes for catch-all routes and localized URL generation in issue #4135.
Out of Scope Changes check	✅ Passed	The source and test changes are directly related to repeatable parameter normalization and the linked trailing-slash bug.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[rastuhacode]

UPD: The PR which resolves the same issue #4136

I kept this open for reference and just in case. Maintainers can close it if they find it unuseful.