From 0105253cadca872b38b9827c4d9de452d6293680 Mon Sep 17 00:00:00 2001
From: overlookmotel <557937+overlookmotel@users.noreply.github.com>
Date: Thu, 1 May 2025 02:03:32 +0000
Subject: [PATCH] feat(span): introduce `format_atom!` macro (#10722)

Introduce a `format_atom!` macro. This behaves the same as `std`'s `format!` macro, but constructs the string directly in arena, and returns an `Atom` instead of a `String`.

```rs
let foo_dot_bar: Atom = format_atom!(&allocator, "{}.{}", foo, bar);
```

Can also be used to avoid creating a temp `String` when creating an `Atom` using a `Display` impl:

```rs
// Before
let atom = ctx.ast.atom(&my_display_type.to_string());
// After
let atom = format_atom!(ctx.ast.allocator, "{my_display_type}");
```
---
 crates/oxc_span/src/atom.rs | 37 +++++++++++++++++++++++++++++++++++++
 crates/oxc_span/src/lib.rs  |  2 ++
 2 files changed, 39 insertions(+)

diff --git a/crates/oxc_span/src/atom.rs b/crates/oxc_span/src/atom.rs
index 02cd9bbfabe86..60f31d727b7dd 100644
--- a/crates/oxc_span/src/atom.rs
+++ b/crates/oxc_span/src/atom.rs
@@ -230,3 +230,40 @@ impl ESTree for Atom<'_> {
         ESTree::serialize(self.as_str(), serializer);
     }
 }
+
+/// Creates an [`Atom`] using interpolation of runtime expressions.
+///
+/// Identical to [`std`'s `format!` macro](std::format), except:
+///
+/// * First argument is the allocator.
+/// * Produces an [`Atom`] instead of a [`String`].
+///
+/// The string is built in the arena, without allocating an intermediate `String`.
+///
+/// # Panics
+///
+/// Panics if a formatting trait implementation returns an error.
+///
+/// # Example
+///
+/// ```
+/// use oxc_allocator::Allocator;
+/// use oxc_span::format_atom;
+/// let allocator = Allocator::new();
+///
+/// let s1 = "foo";
+/// let s2 = "bar";
+/// let formatted = format_atom!(&allocator, "{s1}.{s2}");
+/// assert_eq!(formatted, "foo.bar");
+/// ```
+#[macro_export]
+macro_rules! format_atom {
+    ($alloc:expr, $($arg:tt)*) => {{
+        use ::std::{write, fmt::Write};
+        use $crate::{Atom, __internal::ArenaString};
+
+        let mut s = ArenaString::new_in($alloc);
+        write!(s, $($arg)*).unwrap();
+        Atom::from(s)
+    }}
+}
diff --git a/crates/oxc_span/src/lib.rs b/crates/oxc_span/src/lib.rs
index d8fdbaea95116..02bd38f26977e 100644
--- a/crates/oxc_span/src/lib.rs
+++ b/crates/oxc_span/src/lib.rs
@@ -32,4 +32,6 @@ mod generated {
 pub mod __internal {
     // Used by `format_compact_str!` macro defined in `compact_str.rs`
     pub use compact_str::format_compact;
+    // Used by `format_atom!` macro defined in `atom.rs`
+    pub use oxc_allocator::String as ArenaString;
 }