Regression: 4838 Fusion ParsePartials cache broken in latest 8.3.10 release

[mhsdesign]

there is a nasty regression in the last Neos bugfix release with the Fusion Parser in connection with FileMonitor / local dev mode.

The following happens:

Should: Neos Fusion file change leads to correct re-rendering of the page
Actual: Old code state is rendered, even after Flow has recognised a FileMonitor change

Setup:

• We have a site package that is located under ./DistributionPackages/Customer.Site
• here we change the fusion files

Debugging:

• Observation: the cache for Neos_Fusion_ParsePartials is not invalidated correctly
• when initially caching the parsed fusion file the file path ./DistributionPackages/Customer.Site/.../MyFusion.fusion is converted to an md5 as identifier
• on cache invalidation the flow file monitor returns a file path like ./Packages/Sites/Customer.Site/.../MyFusion.fusion which converted to an md5 as identifier
• the cache flushing is thus not possible as the flow file monitor returns the symlinked path, while fusion operates on actual files.

The symlink has to be resolved consistently in both places (write cache file, invalidate cache file) but that is not always possible when flow for example informs that a file has been deleted. Calling realpath here would just return false and if not correctly handled will resurface the bug that was initially trying to be solved: #4415

Regression due to the mentioned fix: #4838

Possible solutions:

• Fix flows file monitor to operate on actual files and not symlinks (hard)
• Revert the previous change and just silently ignore if a file was removed and keep the cache artefact, which would lead to additional cache entries that are never flushed, and might lead to stale caches if a files is removed then added and changed without flow detecting it.

Affected Neos Versions:

Neos 8.0.17
Neos 8.1.12
Neos 8.2.12
Neos 8.3.10

Thanks for reporting this bug and investigating
@patrickreck @nezaniel @erickloss @lorenzulrich

Slack thread: https://neos-project.slack.com/archives/C050C8FEK/p1708954764784039