Different behavior for custom elements that extends builtin element.

[edoardocavazza]

Describe the bug

I noticed that Svelte behaves differently when it comes to setting properties to a custom element.

When the custom element is autonomous (eg <my-element>), it behaves correctly, passing the attributes as properties.
If instead the custom element extends a builtin element (eg <a is="my-link">) Svelte does not pass the attributes as properties.

The problem I guess comes from this check that checks only the name tag of the node:

svelte/packages/svelte/src/compiler/phases/nodes.js

Line 28 in 09510c8

export function is_custom_element_node(node) {

Reproduction

https://svelte.dev/playground/hello-world?version=5.19.1#H4sIAAAAAAAAE62NsY7CMBBEf2W1DU1IeitEQjRX3B8QpGxgkQyObXk3XFCUfz_5Du4aSqqRnmbmzehpYDS4G0XDAOx4YK8CyqJY4Nk6FjT7GfUecy8DLJ6rbYyl3NhpZj0Jv-LH4DV_osF6Wj8MEPoLH3Uzzz8qA6sPdi7AV0jutIJlaT5DuAIpDHcg1WT7UVlK6H6HHViBSCJ8AhIgiCnEsq7-BE3r6z5BlZPAyqbFae2sv7b4brf_L5V1RU3rsUDlSdFoGnk5LN_Mqu7kZwEAAA==

Logs

System Info

Svelte 5.19.1 (Playground)

Severity

annoyance