From fb64b869c8df08d0ba612aa27132027fa835143d Mon Sep 17 00:00:00 2001
From: "K.J. Valencik" <kjvalencik@gmail.com>
Date: Fri, 10 Jan 2025 17:29:16 -0500
Subject: [PATCH] feat(neon): Allow getting a `&'cx T` from a `Handle<'cx,
 JsBox<T>>`

Resolves https://github.com/neon-bindings/neon/issues/678
---
 crates/neon/src/types_impl/boxed.rs | 31 +++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/crates/neon/src/types_impl/boxed.rs b/crates/neon/src/types_impl/boxed.rs
index 02d3557f6..d1910a5a4 100644
--- a/crates/neon/src/types_impl/boxed.rs
+++ b/crates/neon/src/types_impl/boxed.rs
@@ -259,12 +259,39 @@ impl<T: Finalize + 'static> JsBox<T> {
     }
 }
 
+impl<T: 'static> JsBox<T> {
+    /// Gets a reference to the inner value of a [`JsBox`]. This method is similar to
+    /// [dereferencing](JsBox::deref) a `JsBox` (e.g., `&*boxed`), but the lifetime
+    /// is _safely_ extended to `'cx`.
+    ///
+    /// See also [`Handle<JsBox>::as_inner`].
+    // N.B.: This would be cleaner with https://github.com/rust-lang/rust/issues/44874
+    pub fn deref<'cx>(v: &Handle<'cx, Self>) -> &'cx T {
+        v.as_inner()
+    }
+}
+
+impl<'cx, T: 'static> Handle<'cx, JsBox<T>> {
+    /// Gets a reference to the inner value of a [`JsBox`]. This method is similar to
+    /// [dereferencing](JsBox::deref) a `JsBox` (e.g., `&*boxed`), but the lifetime
+    /// is _safely_ extended to `'cx`.
+    ///
+    /// See also [`JsBox::deref`].
+    pub fn as_inner(&self) -> &'cx T {
+        // # Safety
+        // JS values associated with an in-scope `Context` *cannot* garbage collected. This
+        // value is guaranteed to live at least as long as `'cx`.
+        unsafe { &*self.0.raw_data }
+    }
+}
+
 impl<T: 'static> Deref for JsBox<T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
-        // Safety: This depends on a `Handle<'a, JsBox<T>>` wrapper to provide
-        // a proper lifetime.
+        // # Safety
+        // `T` will live at least as long as `JsBox<T>` because it may not be garbage
+        // collected while in scope and only immutable references can be obtained.
         unsafe { &*self.0.raw_data }
     }
 }