From 8e10e25ded956bf5dcb7f6752e227de4714e0dea Mon Sep 17 00:00:00 2001
From: overlookmotel <557937+overlookmotel@users.noreply.github.com>
Date: Sun, 11 Aug 2024 03:31:45 +0000
Subject: [PATCH] feat(allocator): introduce `Address` (#4810)

Closes #4807.

Introduce `Address`. `Address` can be obtained from a `Box<T>` and can act as a unique identifier for an AST node in arena.

NB: It will also be unique across 2 ASTs in different allocators as long as neither allocator is dropped.
---
 crates/oxc_allocator/src/arena.rs | 15 +++++++++++++++
 crates/oxc_allocator/src/lib.rs   |  2 +-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/crates/oxc_allocator/src/arena.rs b/crates/oxc_allocator/src/arena.rs
index 81459678c..350fbf74d 100644
--- a/crates/oxc_allocator/src/arena.rs
+++ b/crates/oxc_allocator/src/arena.rs
@@ -212,6 +212,21 @@ impl<'alloc, T: Hash> Hash for Vec<'alloc, T> {
     }
 }
 
+/// Memory address of an AST node in arena.
+///
+/// `Address` is generated from a `Box<T>`.
+/// AST nodes in a `Box` in an arena are guaranteed to never move in memory,
+/// so this address acts as a unique identifier for the duration of the arena's existence.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct Address(usize);
+
+impl<'a, T> Box<'a, T> {
+    #[inline]
+    pub fn address(&self) -> Address {
+        Address(ptr::addr_of!(**self) as usize)
+    }
+}
+
 #[cfg(test)]
 mod test {
     use std::hash::{DefaultHasher, Hash, Hasher};
diff --git a/crates/oxc_allocator/src/lib.rs b/crates/oxc_allocator/src/lib.rs
index 7ab4c8ff6..4093dd75d 100644
--- a/crates/oxc_allocator/src/lib.rs
+++ b/crates/oxc_allocator/src/lib.rs
@@ -9,7 +9,7 @@ mod convert;
 
 use bumpalo::Bump;
 
-pub use arena::{Box, String, Vec};
+pub use arena::{Address, Box, String, Vec};
 pub use clone_in::CloneIn;
 pub use convert::{FromIn, IntoIn};