fix: html tag hydration: regard empty claimed_nodes array as content mismatch. fixes #6832

[kelvinsjk]

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

Fixes #6832, where nodes were missing on hydration.

Within the claim_html_tag function, the returned claimed_nodes is sometimes an empty array (due to issues with the claim_space function as investigated by rmunn in discussion in #6832). However, hbirler, in the same thread, mentioned that this error in claims should not cause problems in the correctness of the output. Turns out the intended hydration was not working because an empty claimed_nodes array was being regarded as properly claimed nodes rather than a case of mismatch.

I did not add a test as I was unable to recreate the bug outside of SvelteKit (attempts in test/runtime and test/runtime-browser led to passing tests with output different than when I run the Svelte component in SvelteKit). Will be happy to add one if some guidance is provided as to how to recreate this within the test structure

[changeset-bot]

🦋 Changeset detected

Latest commit: 23688da

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

This PR includes changesets to release 1 package

Name	Type
svelte	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[dummdidumm]

Thank you! Could you add a changeset and a test? If you add one to runtime it should work, as these are run in hydration mode, too, if not specifically turned off.
One thing I'm not sure about yet is what this means for empty each blocks etc. But maybe a test run reveals that.

[kelvinsjk]

Added the test case and changeset.

Thanks for pointing me towards using hydration for the test.

Turns out adding whitespace was what I needed to get a failing test that passes with this PR.