fix: Throw exception in PreviewManager when preview is not available

[akhil1508]

• Resolves: [Bug]: Previews for files show up in external storages even when the previews option for storage is set to off #52858

Summary

• The exception thrown doesn't actually check if previews are disabled at storage or provider level; I fix that in this PR so that storage level disabling of preview works as expected

Before:

• For an external storage mount with previews disabled
  

After:

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[provokateurin]

I'm not sure if this is the right way, but changing a default value in the API should be avoided as it means a breaking change in the behavior. The root of the issue is likely somewhere else.

[akhil1508]

but changing a default value in the API should be avoided as it means a breaking change in the behavior

@provokateurin I agree with your concern generally

However, in this case:

• It doesn't seem like a sensible default to be true as it essentially means that the mount-level disabling of previews is only respected if the forceIcon attribute is set by a client to be false; but that should be respected at the backend by default
• I did check the nextcloud server project code to see if any clients consuming this API there might be affected; doesn't seem like the case to me

[come-nc]

but forceIcon should return an icon if preview is disabled, not compute a preview, no?

[provokateurin]

That's what I think as well and it's why I said that I think the problem is elsewhere.

[akhil1508]

but forceIcon should return an icon if preview is disabled, not compute a preview, no?

@come-nc @provokateurin I was not aware that this was the intention of the parameter; let me dig deeper then

[akhil1508]

@provokateurin @come-nc Please check now. Earlier the exception was thrown only if previews are disabled system-wide; now it is thrown if previews are not available for whatever reason using the isAvailable method

[provokateurin]

Looks sane to me, the method definitely should have used isAvailable() since that checks if the storage allows/supports it.

[provokateurin]

/backport to stable31

[provokateurin]

/backport to stable30

[come-nc]

👍

[come-nc]

CI failure are unrelated for phpunit, and the others are because this comes from a fork.
Good to merge 👍

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