Pass targets for swc/helpers to Rust and only filter them for preset env

packages/core/integration-tests/test/integration/js-export-arrow-support/bar/index.js

@@ -0,0 +1 @@
+export {bar} from "./other.js";

packages/core/integration-tests/test/integration/js-export-arrow-support/bar/other.js

@@ -0,0 +1 @@
+export const bar = "bar";

packages/core/integration-tests/test/integration/js-export-arrow-support/index.js

@@ -0,0 +1,5 @@
+import * as helpers from "@swc/helpers";
+import * as bar from "./bar";
+import * as foo from "foo";
+
+export default [helpers, bar, foo];

packages/core/integration-tests/test/integration/js-export-arrow-support/package.json

@@ -0,0 +1,3 @@
+{
+  "browserslist": "ie 11"
+}

packages/core/integration-tests/test/javascript.js

@@ -5110,6 +5110,14 @@ describe('javascript', function () {
     assert.deepEqual(res, {a: 4});
   });
 
+  it('should not use arrow functions for reexport declarations unless supported', async function () {
+    let b = await bundle(
+      path.join(__dirname, 'integration/js-export-arrow-support/index.js'),
+    );
+    let content = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
+    assert(!content.includes('=>'));
+  });
+
   it('should support import namespace declarations of other ES modules', async function () {
     let b = await bundle(
       path.join(__dirname, 'integration/js-import-namespace/a.js'),

packages/transformers/js/core/src/lib.rs

@@ -91,6 +91,7 @@ pub struct Config {
   is_library: bool,
   is_esm_output: bool,
   trace_bailouts: bool,
+  is_swc_helpers: bool,
 }
 
 #[derive(Serialize, Debug, Default)]
@@ -318,11 +319,16 @@ pub fn transform(config: Config) -> Result<TransformResult, std::io::Error> {
               ..Default::default()
             };
             let versions = targets_to_versions(&config.targets);
-            if let Some(versions) = versions {
-              preset_env_config.targets = Some(Targets::Versions(versions));
-              preset_env_config.shipped_proposals = true;
-              preset_env_config.mode = Some(Entry);
-              preset_env_config.bugfixes = true;
+            if !config.is_swc_helpers {
+              // Avoid transpiling @swc/helpers so that we don't cause infinite recursion.
+              // Filter the versions for preset_env only so that syntax support checks
+              // (e.g. in esm2cjs) still work correctly.
+              if let Some(versions) = versions {
+                preset_env_config.targets = Some(Targets::Versions(versions));
+                preset_env_config.shipped_proposals = true;
+                preset_env_config.mode = Some(Entry);
+                preset_env_config.bugfixes = true;
+              }
             }
 
             let mut diagnostics = vec![];
@@ -384,15 +390,18 @@ pub fn transform(config: Config) -> Result<TransformResult, std::io::Error> {
                   config.insert_node_globals && config.source_type != SourceType::Script
                 ),
                 // Transpile new syntax to older syntax if needed
-                Optional::new(
-                  preset_env(
-                    global_mark,
-                    Some(&comments),
-                    preset_env_config,
-                    Default::default()
-                  ),
-                  config.targets.is_some()
-                ),
+                {
+                  let should_transpile = preset_env_config.targets.is_some();
+                  Optional::new(
+                    preset_env(
+                      global_mark,
+                      Some(&comments),
+                      preset_env_config,
+                      Default::default(),
+                    ),
+                    should_transpile,
+                  )
+                },
                 // Inject SWC helpers if needed.
                 helpers::inject_helpers(),
               );

packages/transformers/js/src/JSTransformer.js

@@ -334,11 +334,6 @@ export default (new Transformer({
       targets = {node: semver.minVersion(asset.env.engines.node)?.toString()};
     }
 
-    // Avoid transpiling @swc/helpers so that we don't cause infinite recursion.
-    if (/@swc[/\\]helpers/.test(asset.filePath)) {
-      targets = null;
-    }
-
     let env: EnvMap = {};
 
     if (!config?.inlineEnvironment) {
@@ -420,6 +415,7 @@ export default (new Transformer({
       is_library: asset.env.isLibrary,
       is_esm_output: asset.env.outputFormat === 'esmodule',
       trace_bailouts: options.logLevel === 'verbose',
+      is_swc_helpers: /@swc[/\\]helpers/.test(asset.filePath),
     });
 
     let convertLoc = loc => {