feat(PageReference): Preview "Page not found" if page is not accessible

[pymnh]

📝 Summary

Change

• Let the backend return empty Reference with accessible = false if current user cannot resolve
• In the refernce widget: If accessible = false, show an informative "Page not found" preview and explain that the page does not seem to exist or that the permissions are missing to view it.
• On click: open a popover to confirm if user really wants to follow the link

Reasoning:

• Currently if I have not the permission to view a collectives page, the ReferenceProvider just falls back to opengraph, even if the URL matches a collective page.
• This is IMO not correct: The collectives preview widget should still be responsible, even if it does not preview the content
• One consideration: The way I did it, neither the name of the collective nor the title of the page are shown to the user. Technically these are not secret information, as they are included in the link. IMO one could also just render the title and change the description to include that the page was not found. I have no strong opinion on this.

🖼️ Screenshots

🏚️ Before

🏡 After

🚧 TODO

• A fallback preview might also make sense for other reference providers and there should be a common way of doing this, so it would be nice to gather consensus if...
  • The accessible property is the right place to indicate that a "resource not found" message should be displayed
  • If the Reference provider should return a link or a completely empty richObject or can sometimes carry some more information? (-> Decks have only numeric ids in their URL, while collectives include Collective name and Page name in the URL, so for collectives, passing on these infos might not be a privacy issue?)
• Add some unit tests

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests
• Documentation (README or documentation) has been updated or is not required

[pymnh]

Psalm error looks unrelated to me, I did not touch the dependencies..

[pymnh]

I just noticed that there is a vue component that might be good to use:

https://nextcloud-vue-components.netlify.app/#/Components/NcEmptyContent

What do you think?

[pymnh]

I removed the Popover confirmation dialog and used NcEmptyContent:

[mejo-]

Thanks @pymnh! Without looking at the code yet, from the screenshots it looks like the not found preview is much larger than the normal preview. I'd expect them to have the same height.

[pymnh]

I am not sure if one can squeeze the NcEmptyContent to the same size as the regular preview.

Should I then rather just revert NcEmptyContent and manually set title, description and icon with fallbacks with same alignment and font size like the regular preview?

[mejo-]

Should I then rather just revert NcEmptyContent and manually set title, description and icon with fallbacks with same alignment and font size like the regular preview?

I would say so, yes. NcEmptyContent has a rather strict structure with everything (icon, title, description) below each other. So I think we're better with not using it here 😉

[pymnh]

The "not found" preview now has the same size as regular page previews