fix: generate valid Path types for routes with optional or rest params, several params in one segment, or escape sequences

[Nic-Polumeyv]

/[[lang]]/about generates the Path member {string}/about, a plain string rather than a template: #16430 appended .slice(1) to a branch whose replacement had already consumed the leading slash, chopping the $. Since resolve() is bounded by Path, resolve('en/about') is rejected while resolve('{string}/about') type checks.

The pathname is now built from the route's segments. An omitted optional param contributes its own pathname instead of absorbing the following /, so xyzabout is no longer admitted, and a second param in one segment (/[foo]-[bar]) no longer leaks in verbatim.

Rest params get the same treatment, since [...path] can match zero segments. Escape sequences are expanded the same way #16570 expands them in resolve, so /[x+2e]well-known contributes .well-known rather than the raw route id.

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 15d2da7:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/15d2da79ecf3bfab3771638325213bbe5f186b61

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16577

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 15d2da7

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[Rich-Harris]

LGTM!

[Nic-Polumeyv]

Needed to tidy up a few things and fix an omission bug. Opening in a couple min!

[vercel]

Additional Suggestion:

Call to undefined remove_group_segments in write_app_types.js throws ReferenceError on the first route, breaking svelte-kit sync type generation.