reset cache when storage possibly change (fix init of tests).

[cheme]

Very small pr to reset root cache when building state (in some other branch my tests did fail due to the root caching when using test externalities).

[bkchr]

Where is this function being used?

[cheme]

On 'assimilate' (did hit that when adding content to test_externalities in another branch), via 'apply_transaction'.

[bkchr]

So we should reset the cache there?

[cheme]

Yes, modifying the storage with the mutable access means you are changing the backend (in normal condition this never happen, storage of trie backend stay the same during the whole processing, but in tests this function can be use).
We could clear cache after changing the backend in the calling function, but it looks safer to do it here (mutable access to trie backend so potentially something change and get invalidated).

(it is just the local cache of child trie roots)

[bkchr]

Hmm all of this feels very dirty.

[cheme]

I can move the the clear_cache after calling backend_storage_mut but it will not prevent future issue.
I would prefer renaming the function to backend_storage_test_modify or something that let the user know storage from a trie backend should not be change this way.

[cheme]

I could also just remove backend_storage_mut, and replace it by trie backend rebuilding (thus using a new empty cache).

[cheme]

Hmm all of this feels very dirty.

I feel that it is more backend_storage_mut that is a bit out of place, and if you audit usage it is mostly for building test or in memory backend as a convenience function (trie backend purpose is to implement backend that is a read api (with some inner mutable access for caching)).

[cheme]

I use this code in #8931 , but with recent refactoring it may not be needed anymore, but in any case it is still a footgun.

[bkchr]

but in any case it is still a footgun.

If we can remove it, perfect.

[bkchr]

Do we still need this?

[cheme]

👍 I did forget it , thanks.

[bkchr]

bot merge

[ghost]

Trying merge.

[ghost]

Bot will approve on the behalf of @bkchr, since they are a team lead, in an attempt to reach the minimum approval count