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feat: Implement JsValue.as_ptr and (bonus) JsValue.downcast_unchecked #3088

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feat: Implement JsValue.as_ptr and (bonus) JsValue.downcast_unchecked #3088

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Commits on May 11, 2023

  1. fix(cli-support): Change lib.rs chmod.

    @Hywan
    Hywan committed May 11, 2023
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  2. feat: Implement JsValue.as_ptr. 

    This patch implements `JsValue.as_ptr`. The idea is to be able to
retrieve the `ptr` value of a `JsValue` from the JS land, which
represents the raw pointer value of the value from within the Wasm
memory.

To achieve this, this patch introduces a new intrinsic:
`__wbindgen_jsval_ptr`, which maps to `Intrinsic::JsvalPtr`, which
returns a (new) `opt_u32`. It generates the following JS code:
`{obj}.ptr`. If `ptr` is absent, it will return `undefined`, so `None`
once on the Rust side, otherwise `Some(u32)`.

The following Rust code is the “old” way of achieving this behavior:

```rust
pub struct JsvalPtr;

let js_val: JsValue = JsvalPtr.into();
let ptr = Reflect::get(&js_val, &JsValue::from_str("ptr").unwrap().as_f64().unwrap() as u32;
```

The following Rust code is the "new” way of achieving this behavior:

```rust
let ptr = js_val.as_ptr().unwrap();
```

The `Reflect` API is not longer necessary.
    @Hywan
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  3. feat: Implement JsValue.downcast_unchecked. 

    Since the introduction of the new `JsValue.as_ptr` method, it is now
possible to implement a new handy method: `JsValue.downcast_unchecked`
(which is unsafe by nature because no check is applied).

`downcast_unchecked` will downcast the `JsValue` to `T::Anchor` where
it implements `RefFromWasmAbi<Abi = u32>`. It returns a `Ref<T>` which
can be deref to `&T`.
    @Hywan
    Hywan committed May 11, 2023
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  4. test: Test JsValue.as_ptr and .downcast_unchecked.

    @Hywan
    Hywan committed May 11, 2023
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  5. doc: Add a Safety Section to JsValue.downcast_unchecked.

    @Hywan
    Hywan committed May 11, 2023
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  6. fix: ptr has been renamed to __wbg_ptr.

    @Hywan
    Hywan committed May 11, 2023
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