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58 lines
1.7 KiB
Rust
58 lines
1.7 KiB
Rust
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
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use deno_core::v8;
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use std::mem::transmute;
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use std::ops::Deref;
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use std::os::raw::c_void;
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use std::ptr::NonNull;
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/// An FFI-opaque, nullable wrapper around v8::Local<v8::Value>.
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/// rusty_v8 Local handle cannot be empty but napi_value can be.
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#[repr(transparent)]
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#[derive(Clone, Copy, Debug)]
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pub struct NapiValue<'s>(
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Option<NonNull<v8::Value>>,
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std::marker::PhantomData<&'s ()>,
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);
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pub type napi_value<'s> = NapiValue<'s>;
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impl<'s> Deref for napi_value<'s> {
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type Target = Option<v8::Local<'s, v8::Value>>;
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fn deref(&self) -> &Self::Target {
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// SAFETY: It is safe to transmute `Option<NonNull<T>>` to `Option<*const T>`.
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// v8::Local guarantees that *const T is not null but napi_value *can* be null.
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unsafe { transmute::<&Self, &Self::Target>(self) }
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}
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}
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impl<'s, T> From<v8::Local<'s, T>> for napi_value<'s>
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where
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v8::Local<'s, T>: Into<v8::Local<'s, v8::Value>>,
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{
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fn from(v: v8::Local<'s, T>) -> Self {
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// SAFETY: It is safe to cast v8::Local<T> that implements Into<v8::Local<v8::Value>>.
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// `fn into(self)` transmutes anyways.
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Self(unsafe { transmute(v) }, std::marker::PhantomData)
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}
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}
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const _: () = {
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assert!(
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std::mem::size_of::<napi_value>() == std::mem::size_of::<*mut c_void>()
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);
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// Assert "nullable pointer optimization" on napi_value
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unsafe {
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type Src<'a> = napi_value<'a>;
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type Dst = usize;
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assert!(std::mem::size_of::<Src>() == std::mem::size_of::<Dst>());
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union Transmute<'a> {
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src: Src<'a>,
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dst: Dst,
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}
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Transmute {
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src: NapiValue(None, std::marker::PhantomData),
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}
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.dst
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};
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};
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