fix: allow leading and trailing comments in mustache tag

[BlueGreenMagick]

Fixes #7456

This PR allows having leading and trailing comments in mustache expressions. This can be useful when disabling eslint for expression in expression, like following

<script lang="ts">
  export let num: number;
</script>

{num ?? num /* eslint-disable-line */ }

This PR does not change that having only comments in mustache does not work, such as {/* comment */} as often used in React.

trailingComments are attached to parent node instead when parent.end === node.end, so that checking for end position of 'js expression + comment' can be done by checking for end position of the root node's last trailing comment.

Further

If this PR is accepted, the print(ast) function of esrap (and perhaps code-red as well) needs to be changed. An assumption is made that there can only be at most 1 trailingComments, but this PR changes it to potentially have multiple comments. So it causes a minor bug where the 2nd+ trailing comments are not printed when printing js from ast.

https://github.com/Rich-Harris/esrap/blob/2b9561c679ed38cc216e7d481a323bfef387a022/src/handlers.js#L59-L61

If needed, I can create a PR for that as well.

[changeset-bot]

🦋 Changeset detected

Latest commit: ab831f5

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

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[Rich-Harris]

Thank you! Apologies for taking a while to get to this PR — it looks great and ready to go from my perspective, but I just want to get a +1 from @dummdidumm first in case there are any language-tools implications — hopefully this will self-fix once the updated version is released, but Prettier currently balks at this and the syntax highlighting is off:

[dummdidumm]

Everything works - one has to run pnpm build to get the CJS version of the compiler (which language tools use) and then restart the Svelte extension to see such changes in effect.