#2587 introduced a breaking change in the serialized format of `RoomInfo`, changing the `event`
field format in particular, without a migration. As a result, this lead to users state stores
being invalidated for containing incorrect data, and thus being logged out.
This mitigates the issue by making sure that the LatestEvent type is either deserialized as its
newer format (aka `SerializedLatestEvent`) or its older format (aka `SyncTimelineEvent`). This
way, we maintain compatibility with the previous format. We always serialize to the new one, so
we'd only run this migration once.
- `content` is now of type `RoomMessageEventContentWithoutRelation`,
the relation was previously always overwritten if set
- `add_mentions` is now inferred from `content.mentions`
This adds a new `StoreTransaction` type, that wraps a `StoreCache` and a `Store`. The idea is that it will allow write access to the `Store` (and maintains the cache at the same time), while the `Store::cache` method will only give read-only access to the store's content.
Another new data type is introduced, `PendingChanges`, that reflects `Changes` but for fields that are properly maintained in the `StoreCache` and that one can write in the `StoreTransaction`. In the future, it wouldn't be possible to use `save_pending_changes` from the outside of a `StoreTransaction` context.
The layering is the following:
- `Store` wraps the `DynCryptoStore`, contains a reference to a `StoreCache`.
- When read-only access is sufficient, one can get a handle to the cache with `Store::cache()`.
- When a write happens, then one can create a `StoreTransaction` (later, only one at a time will be allowed, by putting the `StoreCache` behind a `RwLock`; this has been deferred to not make the PR grow too much).
- Any field in the `StoreCache` will get a method to get a reference to the cached thing: it will either load from the DB if not cached, or return the previously cached value.
- Any field that can be written to will get a method to get a mutable reference in the `StoreTransaction`: it will either load from the cache into a `PendingChanges` scratch pad, or return the scratchpad temporary value.
- When a `StoreTransaction::commit()` happens, fields are backpropagated into the DB *and* the cache.
Then, this `StoreTransaction` is used to update a `ReadOnlyAccount` in multiple places (and usage of `ReadOnlyAccount` is minimized so as not to require a transaction or cache function call as much as possible). With this, the read-only account only exists transiently, and it's only stored long-term in the cache.
Followup PRs include:
- making the `ReadOnlyAccount` not cloneable
- remove inner mutability from the `ReadOnlyAccount`
- add a `RwLock` on the `StoreTransaction`
Part of https://github.com/matrix-org/matrix-rust-sdk/issues/2624 + https://github.com/matrix-org/matrix-rust-sdk/issues/2000.
---
* crypto: Replace some uses of `ReadOnlyAccount` with `StaticAccountData` and identify tests
* crypto: introduce `StoreTransaction` to modify a `ReadOnlyAccount`
* crypto: introduce `save_pending_changes`, aka `save_changes` v2
* crypto: Start using `StoreTransaction`s to save the account, get rid of `Store::save_account` + `Account::save`
* crypto: use `StoreTransaction` to save an account in `keys_for_upload`
* crypto: use `StoreTransaction` and the cache in more places
* crypto: remove `Account` from the `Changes` \o/
* crypto: remove last (test-only) callers of `Store::account()`
* crypto: move `ReadOnlyAccount` inside the cache only
* crypto: use `ReadOnlyAccount` and `Account` in fewer places
whenever we can use `StaticAccountData` in place.
* crypto: make tests rely less on OlmMachine
* crypto: Don't put the `ReadOnlyAccount` behind a RwLock just yet
+ clippy
Kévin Commaille