Bump leptos_meta from 0.4.1 to 0.5.0

[dependabot[bot]]

Bumps leptos_meta from 0.4.1 to 0.5.0.

Release notes

Sourced from leptos_meta's releases.

v0.5.0

v0.5.0

Goodbye, Scope

This long-awaited release changes the nature of the reactive system by removing the entire concept of explicit Scope and the ubiquitous cx variable.

The primary impetus behind this change is that it increases the correctness of the behavior of the reactive system, and fixes several persistent issues.

From 0.0 to 0.4, Leptos allocated signals in a dedicated Scope, which was ubiquitous in APIs. This had several drawbacks

1. Ergonomics: It was annoying additional boilerplate to pass around.
2. Trait implementations: Needing an additional Scope argument on many functions prevented us from implementing many traits that could not take an additional argument on signals, like From, Serialize/Deserialize.
3. Correctness: Two characteristics made this system somewhat broken

• The Scope was stored in a variable that was passed around, meaning that the “wrong” scope could be passed into functions (most frequently Resource::read()). If, for example, a derived signal or memo read from a resource in the component body, and was called under a Suspense lower in the tree, the Scope used would be from the parent component, not the Suspense. This was just wrong, but involved wrapping the function in another closure to pass in the correct Scope.
• It was relatively easy to create situations, that could leak memory unless child Scopes were manually created and disposed, or in which on_cleanup was never called. (See #802 and #918 for more background.)

The solution to this problem was to do what I should have been doing a year ago, and merge the memory allocation function of Scope into the reactive graph itself, which already handles reactive unsubscriptions and cleanup. JavaScript doesn’t deal with memory management, but SolidJS handles its onCleanup through a concept of reactive ownership; disposing of memory for our signals is really just a case of cleanup on an effect or memo rerunning.

Essentially, rather than being owned by a Scope every signal, effect, or memo is now owned by its parent effect or memo. (If it’s in an untrack, there’s no reactive observer but the reactive owner remains.) Every time an effect or memo reruns, it disposes of everything “beneath” it in the tree. This makes sense: for a signal to be owned by an effect/memo, it must have been created during the previous run, and will be recreated as needed during the next run, so this is the perfect time to dispose of it.

It also has the fairly large benefit of removing the need to pass cx or Scope variables around at all, and allowing the implementation of a bunch of different traits on the various signal types.

Now that we don't need an extra Scope argument to construct them, many of the signal types now implement Serialize/Deserialize directly, as well as From<T>. This should make it significantly easier to do things like "reactively serialize a nested data structure in a create_effect" — this removed literally dozens of lines of serialization/deserialization logic and a custom DTO from the todomvc example. Serializing a signal simply serializes its value, in a reactive way; deserializing into a signal creates a new signal containing that deserialized value.

Migration is fairly easy. 95% of apps will migrate completely by making the following string replacements:

1. cx: Scope, => (empty string)
2. cx: Scope => (empty string)
3. cx, => (empty string)
4. (cx) => ()
5. |cx| => ||
6. Scope, => (empty string)
7. Scope => (empty string) as needed
8. You may have some |_, _| that become |_| or |_| that become ||, particularly for the fallback props on <Show/> and <ErrorBoundary/>.

Basically, there is no longer a Scope type, and anything that used to take it can simply be deleted.

For the 5%: if you were doing tricky things like storing a Scope somewhere in a struct or variable and then reusing it, you should be able to achieve the same result by storing Owner::current() somewhere and then later using it in with_owner(owner, move || { /* ... */ }). If you have issues with this kind of migration, please let me know by opening an issue or discussion thread and we can work through the migration.

Islands

This release contains an initial, but very functional, implementation of the “islands architecture” for Leptos.

... (truncated)

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Superseded by #194.