2 files changed, 77 insertions, 12 deletions
diff --git a/ext/napi/lib.rs b/ext/napi/lib.rs
index 5bcb29643..5fd3085ca 100644
--- a/ext/napi/lib.rs
+++ b/ext/napi/lib.rs
@@ -12,18 +12,12 @@ use deno_core::futures::channel::mpsc;
 use deno_core::futures::StreamExt;
 use deno_core::op;
 use deno_core::serde_v8;
-pub use deno_core::v8;
 use deno_core::Extension;
 use deno_core::OpState;
 use std::cell::RefCell;
-pub use std::ffi::CStr;
 use std::ffi::CString;
-pub use std::mem::transmute;
-pub use std::os::raw::c_char;
-pub use std::os::raw::c_void;
 use std::path::Path;
 use std::path::PathBuf;
-pub use std::ptr;
 use std::task::Poll;
 use std::thread_local;
 
@@ -33,11 +27,21 @@ use libloading::os::unix::*;
 #[cfg(windows)]
 use libloading::os::windows::*;
 
+// Expose common stuff for ease of use.
+// `use deno_napi::*`
+pub use deno_core::v8;
+pub use std::ffi::CStr;
+pub use std::mem::transmute;
+pub use std::os::raw::c_char;
+pub use std::os::raw::c_void;
+pub use std::ptr;
+pub use value::napi_value;
+
 pub mod function;
+mod value;
 
 pub type napi_status = i32;
 pub type napi_env = *mut c_void;
-pub type napi_value = *mut c_void;
 pub type napi_callback_info = *mut c_void;
 pub type napi_deferred = *mut c_void;
 pub type napi_ref = *mut c_void;
@@ -81,7 +85,7 @@ type napi_addon_register_func =
   extern "C" fn(env: napi_env, exports: napi_value) -> napi_value;
 
 #[repr(C)]
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub struct NapiModule {
   pub nm_version: i32,
   pub nm_flags: u32,
@@ -211,7 +215,10 @@ pub struct napi_type_tag {
 }
 
 pub type napi_callback = Option<
-  unsafe extern "C" fn(env: napi_env, info: napi_callback_info) -> napi_value,
+  unsafe extern "C" fn(
+    env: napi_env,
+    info: napi_callback_info,
+  ) -> napi_value<'static>,
 >;
 
 pub type napi_finalize = unsafe extern "C" fn(
@@ -250,13 +257,13 @@ pub const napi_default_jsproperty: napi_property_attributes =
 
 #[repr(C)]
 #[derive(Copy, Clone, Debug)]
-pub struct napi_property_descriptor {
+pub struct napi_property_descriptor<'a> {
   pub utf8name: *const c_char,
-  pub name: napi_value,
+  pub name: napi_value<'a>,
   pub method: napi_callback,
   pub getter: napi_callback,
   pub setter: napi_callback,
-  pub value: napi_value,
+  pub value: napi_value<'a>,
   pub attributes: napi_property_attributes,
   pub data: *mut c_void,
 }
diff --git a/ext/napi/value.rs b/ext/napi/value.rs
new file mode 100644
index 000000000..bb3966593
--- /dev/null
+++ b/ext/napi/value.rs
@@ -0,0 +1,58 @@
+// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
+
+use deno_core::v8;
+use std::mem::transmute;
+use std::ops::Deref;
+use std::os::raw::c_void;
+use std::ptr::NonNull;
+
+/// An FFI-opaque, nullable wrapper around v8::Local<v8::Value>.
+/// rusty_v8 Local handle cannot be empty but napi_value can be.
+#[repr(transparent)]
+#[derive(Clone, Copy, Debug)]
+pub struct NapiValue<'s>(
+  Option<NonNull<v8::Value>>,
+  std::marker::PhantomData<&'s ()>,
+);
+
+pub type napi_value<'s> = NapiValue<'s>;
+
+impl<'s> Deref for napi_value<'s> {
+  type Target = Option<v8::Local<'s, v8::Value>>;
+  fn deref(&self) -> &Self::Target {
+    // SAFETY: It is safe to transmute `Option<NonNull<T>>` to `Option<*const T>`.
+    //         v8::Local guarantees that *const T is not null but napi_value *can* be null.
+    unsafe { transmute::<&Self, &Self::Target>(self) }
+  }
+}
+
+impl<'s, T> From<v8::Local<'s, T>> for napi_value<'s>
+where
+  v8::Local<'s, T>: Into<v8::Local<'s, v8::Value>>,
+{
+  fn from(v: v8::Local<'s, T>) -> Self {
+    // SAFETY: It is safe to cast v8::Local<T> that implements Into<v8::Local<v8::Value>>.
+    //         `fn into(self)` transmutes anyways.
+    Self(unsafe { transmute(v) }, std::marker::PhantomData)
+  }
+}
+
+const _: () = {
+  assert!(
+    std::mem::size_of::<napi_value>() == std::mem::size_of::<*mut c_void>()
+  );
+  // Assert "nullable pointer optimization" on napi_value
+  unsafe {
+    type Src<'a> = napi_value<'a>;
+    type Dst = usize;
+    assert!(std::mem::size_of::<Src>() == std::mem::size_of::<Dst>());
+    union Transmute<'a> {
+      src: Src<'a>,
+      dst: Dst,
+    }
+    Transmute {
+      src: NapiValue(None, std::marker::PhantomData),
+    }
+    .dst
+  };
+};