feat(allocator): introduce CloneIn trait. (#4726)

Introduce the trait discussed in #4284.

crates/oxc_allocator/src/clone_in.rs

@@ -0,0 +1,91 @@
+use std::cell::Cell;
+
+use crate::{Allocator, Box, Vec};
+
+/// A trait to explicitly clone an object into an arena allocator.
+///
+/// As a convention `Cloned` associated type should always be the same as `Self`,
+/// It'd only differ in the lifetime, Here's an example:
+///
+/// ```
+/// impl<'old_alloc, 'new_alloc> CloneIn<'new_alloc> for Struct<'old_alloc> {
+///     type Cloned = Struct<'new_alloc>;
+///     fn clone_in(&self, alloc: &'new_alloc Allocator) -> Self::Cloned {
+///         Struct { a: self.a.clone_in(alloc), b: self.b.clone_in(alloc) }
+///     }
+/// }
+/// ```
+///
+/// Implementations of this trait on non-allocated items usually short-circuit to `Clone::clone`;
+/// However, it **isn't** guaranteed.
+///
+pub trait CloneIn<'new_alloc>: Sized {
+    type Cloned;
+
+    fn clone_in(&self, alloc: &'new_alloc Allocator) -> Self::Cloned;
+}
+
+impl<'alloc, T, C> CloneIn<'alloc> for Option<T>
+where
+    T: CloneIn<'alloc, Cloned = C>,
+{
+    type Cloned = Option<C>;
+    fn clone_in(&self, alloc: &'alloc Allocator) -> Self::Cloned {
+        self.as_ref().map(|it| it.clone_in(alloc))
+    }
+}
+
+impl<'old_alloc, 'new_alloc, T, C> CloneIn<'new_alloc> for Box<'old_alloc, T>
+where
+    T: CloneIn<'new_alloc, Cloned = C>,
+{
+    type Cloned = Box<'new_alloc, C>;
+    fn clone_in(&self, alloc: &'new_alloc Allocator) -> Self::Cloned {
+        Box::new_in(self.as_ref().clone_in(alloc), alloc)
+    }
+}
+
+impl<'old_alloc, 'new_alloc, T, C> CloneIn<'new_alloc> for Vec<'old_alloc, T>
+where
+    T: CloneIn<'new_alloc, Cloned = C>,
+{
+    type Cloned = Vec<'new_alloc, C>;
+    fn clone_in(&self, alloc: &'new_alloc Allocator) -> Self::Cloned {
+        Vec::from_iter_in(self.iter().map(|it| it.clone_in(alloc)), alloc)
+    }
+}
+
+impl<'alloc, T: Copy> CloneIn<'alloc> for Cell<T> {
+    type Cloned = Cell<T>;
+    fn clone_in(&self, _: &'alloc Allocator) -> Self::Cloned {
+        Cell::new(self.get())
+    }
+}
+
+impl<'old_alloc, 'new_alloc> CloneIn<'new_alloc> for &'old_alloc str {
+    type Cloned = &'new_alloc str;
+    fn clone_in(&self, alloc: &'new_alloc Allocator) -> Self::Cloned {
+        alloc.alloc_str(self)
+    }
+}
+
+macro_rules! impl_clone_in {
+    ($($t:ty)*) => {
+        $(
+            impl<'alloc> CloneIn<'alloc> for $t {
+                type Cloned = Self;
+                #[inline(always)]
+                fn clone_in(&self, _: &'alloc Allocator) -> Self {
+                    *self
+                }
+            }
+        )*
+    }
+}
+
+impl_clone_in! {
+    usize u8 u16 u32 u64 u128
+    isize i8 i16 i32 i64 i128
+    f32 f64
+    bool char
+}

crates/oxc_allocator/src/lib.rs

@@ -4,11 +4,13 @@ use std::{
 };
 
 mod arena;
+mod clone_in;
 mod convert;
 
 use bumpalo::Bump;
 
 pub use arena::{Box, String, Vec};
+pub use clone_in::CloneIn;
 pub use convert::{FromIn, IntoIn};
 
 #[derive(Default)]