From 06f4dcc0d11012214fccfd700183415a76ca1248 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Wed, 13 Sep 2023 18:00:24 +0200
Subject: [PATCH 1/2] Set ascii_only for swc emit

---
 .../core/integration-tests/test/javascript.js | 20 +++++++++++++++++++
 packages/transformers/js/core/src/lib.rs      |  5 +++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/packages/core/integration-tests/test/javascript.js b/packages/core/integration-tests/test/javascript.js
index 35e597a6e1b..65f185192cb 100644
--- a/packages/core/integration-tests/test/javascript.js
+++ b/packages/core/integration-tests/test/javascript.js
@@ -6365,6 +6365,26 @@ describe('javascript', function () {
     assert.deepEqual(output.default, {color: 'blue'});
   });
 
+  it('should retain unicode escape sequences', async function () {
+    await fsFixture(overlayFS, __dirname)`
+        src/index.js:
+          export default ['\\u0085', '\\u200b', '\\ufffe'];
+      `;
+
+    let b = await bundle(path.join(__dirname, 'src/index.js'), {
+      inputFS: overlayFS,
+    });
+
+    let output = (await run(b)).default;
+    assert.deepEqual(output, ['\u0085', '\u200b', '\ufffe']);
+
+    let contents = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
+    assert.equal(contents.match(/\\/g).length, 3);
+    assert(!contents.includes('\u0085'));
+    assert(!contents.includes('\u200b'));
+    assert(!contents.includes('\ufffe'));
+  });
+
   for (let shouldScopeHoist of [false, true]) {
     let options = {
       defaultTargetOptions: {
diff --git a/packages/transformers/js/core/src/lib.rs b/packages/transformers/js/core/src/lib.rs
index 8a7aa52777f..b2801f367a4 100644
--- a/packages/transformers/js/core/src/lib.rs
+++ b/packages/transformers/js/core/src/lib.rs
@@ -566,8 +566,9 @@ fn emit(
         None
       },
     ));
-    let config =
-      swc_core::ecma::codegen::Config::default().with_target(swc_core::ecma::ast::EsVersion::Es5);
+    let config = swc_core::ecma::codegen::Config::default()
+      .with_target(swc_core::ecma::ast::EsVersion::Es5)
+      .with_ascii_only(true);
     let mut emitter = swc_core::ecma::codegen::Emitter {
       cfg: config,
       comments: Some(&comments),

From c4f1ce1e4a0adebe65ba502f3ac5500824985c73 Mon Sep 17 00:00:00 2001
From: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
Date: Sat, 16 Sep 2023 15:08:54 +0200
Subject: [PATCH 2/2] Add comments

---
 packages/core/integration-tests/test/javascript.js | 1 +
 packages/transformers/js/core/src/lib.rs           | 1 +
 2 files changed, 2 insertions(+)

diff --git a/packages/core/integration-tests/test/javascript.js b/packages/core/integration-tests/test/javascript.js
index 65f185192cb..1c63553f088 100644
--- a/packages/core/integration-tests/test/javascript.js
+++ b/packages/core/integration-tests/test/javascript.js
@@ -6366,6 +6366,7 @@ describe('javascript', function () {
   });
 
   it('should retain unicode escape sequences', async function () {
+    // See issue #8877
     await fsFixture(overlayFS, __dirname)`
         src/index.js:
           export default ['\\u0085', '\\u200b', '\\ufffe'];
diff --git a/packages/transformers/js/core/src/lib.rs b/packages/transformers/js/core/src/lib.rs
index b2801f367a4..5fd47373db9 100644
--- a/packages/transformers/js/core/src/lib.rs
+++ b/packages/transformers/js/core/src/lib.rs
@@ -568,6 +568,7 @@ fn emit(
     ));
     let config = swc_core::ecma::codegen::Config::default()
       .with_target(swc_core::ecma::ast::EsVersion::Es5)
+      // Make sure the output works regardless of whether it's loaded with the correct (utf8) encoding
       .with_ascii_only(true);
     let mut emitter = swc_core::ecma::codegen::Emitter {
       cfg: config,