feat: support OutputOptions#externalLiveBindings (#1979)

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### Description

<!-- Please insert your description here and provide especially info
about the "what" this PR is solving -->

crates/rolldown/src/utils/chunk/render_chunk_exports.rs

@@ -82,14 +82,21 @@ pub fn render_chunk_exports(
 
                 match export_mode {
                   Some(OutputExports::Named) => {
-                    format!(
-                      "Object.defineProperty(exports, '{exported_name}', {{
+                    if !options.external_live_bindings
+                      && export_ref
+                        .is_created_by_import_from_external(&link_output.module_table.modules)
+                    {
+                      format!("exports['{exported_name}'] = {canonical_name}")
+                    } else {
+                      format!(
+                        "Object.defineProperty(exports, '{exported_name}', {{
   enumerable: true,
   get: function () {{
     return {canonical_name};
   }}
 }});"
-                    )
+                      )
+                    }
                   }
                   Some(OutputExports::Default) => {
                     if matches!(options.format, OutputFormat::Cjs) {

crates/rolldown/src/utils/normalize_options.rs

@@ -121,6 +121,7 @@ pub fn normalize_options(mut raw_options: crate::BundlerOptions) -> NormalizeOpt
     inject: raw_options.inject.unwrap_or_default(),
     oxc_inject_global_variables_config,
     extend: raw_options.extend.unwrap_or(false),
+    external_live_bindings: raw_options.external_live_bindings.unwrap_or(true),
   };
 
   NormalizeOptionsReturn { options: normalized, resolve_options: raw_resolve }

crates/rolldown/tests/rolldown/function/external_live_bindings/_config.json

@@ -0,0 +1,7 @@
+{
+  "config": {
+    "external": ["node:fs"],
+    "format": "cjs",
+    "externalLiveBindings": false
+  }
+}

crates/rolldown/tests/rolldown/function/external_live_bindings/artifacts.snap

@@ -0,0 +1,27 @@
+---
+source: crates/rolldown_testing/src/integration_test.rs
+---
+# Assets
+
+## main.cjs
+
+```js
+"use strict";
+
+const { read, readFile, readFileSync, readSync } = __toESM(require("node:fs"));
+
+//#region main.js
+const nonExternal = "nonExternal";
+
+//#endregion
+Object.defineProperty(exports, 'nonExternal', {
+  enumerable: true,
+  get: function () {
+    return nonExternal;
+  }
+});
+exports['read'] = read
+exports['readFile'] = readFile
+exports['readFileSync'] = readFileSync
+exports['readSync'] = readSync
+```

crates/rolldown/tests/rolldown/function/external_live_bindings/indirect.js

@@ -0,0 +1,3 @@
+export { read } from 'node:fs'
+import { readSync } from 'node:fs'
+export { readSync }

crates/rolldown/tests/rolldown/function/external_live_bindings/main.js

@@ -0,0 +1,8 @@
+export { readFile } from 'node:fs';
+import { readFileSync } from 'node:fs';
+
+export { read, readSync } from './indirect'
+
+export { readFileSync };
+
+export const nonExternal = 'nonExternal';

crates/rolldown/tests/snapshots/integration_rolldown__filename_with_hash.snap

@@ -1591,6 +1591,10 @@ expression: "snapshot_outputs.join(\"\\n\")"
 - main-!~{000}~.mjs => main-91SdaZrf.mjs
 - share-!~{002}~.mjs => share-Ak_TT_yj.mjs
 
+# tests/rolldown/function/external_live_bindings
+
+- main-!~{000}~.cjs => main-gvGF4Vpz.cjs
+
 # tests/rolldown/function/format/app/multiple_entry_modules
 
 - cube-!~{002}~.mjs => cube-UC9SFjeM.mjs

crates/rolldown_binding/src/options/binding_output_options/mod.rs

@@ -39,7 +39,7 @@ pub struct BindingOutputOptions {
   #[napi(ts_type = "'default' | 'named' | 'none' | 'auto'")]
   pub exports: Option<String>,
   pub extend: Option<bool>,
-  // externalLiveBindings: boolean;
+  pub external_live_bindings: Option<bool>,
   // footer: () => string | Promise<string>;
   #[derivative(Debug = "ignore")]
   #[serde(skip_deserializing)]
@@ -91,6 +91,7 @@ pub struct BindingOutputOptions {
   // strict: boolean;
   // systemNullSetters: boolean;
   // validate: boolean;
+
   // --- Enhanced options
   pub minify: Option<bool>,
 }

crates/rolldown_binding/src/utils/normalize_binding_options.rs

@@ -155,6 +155,7 @@ pub fn normalize_binding_options(
     inject: input_options
       .inject
       .map(|inner| inner.into_iter().map(normalize_binding_inject_import).collect()),
+    external_live_bindings: output_options.external_live_bindings,
   };
 
   #[cfg(not(target_family = "wasm"))]

crates/rolldown_common/src/inner_bundler_options/mod.rs

@@ -107,6 +107,7 @@ pub struct BundlerOptions {
   pub define: Option<FxIndexMap<String, String>>,
   pub extend: Option<bool>,
   pub inject: Option<Vec<InjectImport>>,
+  pub external_live_bindings: Option<bool>,
 }
 
 #[cfg(feature = "deserialize_bundler_options")]

crates/rolldown_common/src/inner_bundler_options/types/normalized_bundler_options.rs

@@ -16,6 +16,7 @@ use super::{
 };
 use crate::{EsModuleFlag, InjectImport, InputItem, ModuleType};
 
+#[allow(clippy::struct_excessive_bools)] // Using raw booleans is more clear in this case
 #[derive(Debug)]
 pub struct NormalizedBundlerOptions {
   // --- Input
@@ -53,4 +54,5 @@ pub struct NormalizedBundlerOptions {
   pub define: Vec<(/* Target to be replaced */ String, /* Replacement */ String)>,
   pub inject: Vec<InjectImport>,
   pub oxc_inject_global_variables_config: InjectGlobalVariablesConfig,
+  pub external_live_bindings: bool,
 }

crates/rolldown_common/src/types/symbol_ref.rs

@@ -1,6 +1,7 @@
 use oxc::semantic::SymbolId;
+use rustc_hash::FxHashSet;
 
-use crate::ModuleIdx;
+use crate::{IndexModules, Module, ModuleIdx, Specifier};
 
 /// Crossing module ref between symbols
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -14,3 +15,41 @@ impl From<(ModuleIdx, SymbolId)> for SymbolRef {
     Self { owner: value.0, symbol: value.1 }
   }
 }
+
+impl SymbolRef {
+  pub fn is_created_by_import_from_external(&self, modules: &IndexModules) -> bool {
+    self.inner_is_created_by_import_from_external(modules, &mut FxHashSet::default())
+  }
+  fn inner_is_created_by_import_from_external(
+    self,
+    modules: &IndexModules,
+    visited: &mut FxHashSet<SymbolRef>,
+  ) -> bool {
+    let is_not_inserted_before = visited.insert(self);
+    if !is_not_inserted_before {
+      // We are in a cycle
+      return false;
+    }
+
+    let Module::Ecma(owner) = &modules[self.owner] else { return false };
+
+    let Some(named_import) = owner.named_imports.get(&self) else {
+      return false;
+    };
+
+    let rec = &owner.import_records[named_import.record_id];
+
+    match &modules[rec.resolved_module] {
+      Module::Ecma(ecma) => {
+        let Specifier::Literal(imported) = &named_import.imported else {
+          return false;
+        };
+        let Some(named_export) = ecma.named_exports.get(imported) else {
+          return false;
+        };
+        named_export.referenced.is_created_by_import_from_external(modules)
+      }
+      Module::External(_) => true,
+    }
+  }
+}

crates/rolldown_testing/_config.schema.json

@@ -154,6 +154,12 @@
             "type": "string"
           }
         },
+        "externalLiveBindings": {
+          "type": [
+            "boolean",
+            "null"
+          ]
+        },
         "footer": {
           "type": [
             "string",

packages/rolldown/src/binding.d.ts

@@ -237,6 +237,7 @@ export interface BindingOutputOptions {
   esModule?: boolean | 'if-default-prop'
   exports?: 'default' | 'named' | 'none' | 'auto'
   extend?: boolean
+  externalLiveBindings?: boolean
   footer?: (chunk: RenderedChunk) => MaybePromise<VoidNullable<string>>
   format?: 'es' | 'cjs' | 'iife'
   globals?: Record<string, string>

packages/rolldown/src/options/bindingify-output-options.ts

@@ -52,6 +52,7 @@ export function bindingifyOutputOptions(
     // TODO(sapphi-red): support parallel plugins
     plugins: [],
     minify: outputOptions.minify,
+    externalLiveBindings: outputOptions.externalLiveBindings,
   }
 }
 

packages/rolldown/src/options/output-options.ts

@@ -49,6 +49,7 @@ const outputOptionsSchema = z.strictObject({
   minify: z.boolean().optional(),
   name: z.string().optional(),
   globals: z.record(z.string()).optional(),
+  externalLiveBindings: z.boolean().optional(),
 })
 
 export const outputCliOptionsSchema = outputOptionsSchema