feat: generate default export for cjs entry (#219)

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### Description

Requirement for pre-bundling react and react-dom.
<!-- Please insert your description here and provide especially info about the "what" this PR is solving -->

### Test Plan

<!-- e.g. is there anything you'd like reviewers to focus on? -->

---

crates/rolldown/src/bundler/bundle/bundle.rs

@@ -288,7 +288,7 @@ impl<'a> Bundle<'a> {
       .iter()
       .enumerate()
       .map(|(_chunk_id, c)| {
-        let content = c.render(self.graph, &chunk_graph).unwrap();
+        let content = c.render(self.graph, &chunk_graph, self.output_options).unwrap();
 
         Asset { file_name: c.file_name.clone().unwrap(), content }
       })

crates/rolldown/src/bundler/chunk/chunk.rs

@@ -63,7 +63,12 @@ impl Chunk {
   }
 
   #[allow(clippy::unnecessary_wraps)]
-  pub fn render(&self, graph: &Graph, chunk_graph: &ChunkGraph) -> BatchedResult<String> {
+  pub fn render(
+    &self,
+    graph: &Graph,
+    chunk_graph: &ChunkGraph,
+    output_options: &NormalizedOutputOptions,
+  ) -> BatchedResult<String> {
     use rayon::prelude::*;
     let mut joiner = Joiner::with_options(JoinerOptions { separator: Some("\n".to_string()) });
     joiner.append(self.render_imports_for_esm(graph, chunk_graph));
@@ -81,7 +86,7 @@ impl Chunk {
         joiner.append(item);
       });
 
-    if let Some(exports) = self.render_exports_for_esm(graph) {
+    if let Some(exports) = self.render_exports(graph, output_options) {
       joiner.append(exports);
     }
 

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

@@ -1,11 +1,31 @@
+use rolldown_common::WrapKind;
 use string_wizard::MagicString;
 
-use crate::bundler::graph::graph::Graph;
+use crate::bundler::{
+  graph::graph::Graph,
+  options::{normalized_output_options::NormalizedOutputOptions, output_options},
+};
 
 use super::chunk::Chunk;
 
 impl Chunk {
-  pub fn render_exports_for_esm(&self, graph: &Graph) -> Option<MagicString<'static>> {
+  pub fn render_exports(
+    &self,
+    graph: &Graph,
+    output_options: &NormalizedOutputOptions,
+  ) -> Option<MagicString<'static>> {
+    if let Some(entry) = self.entry_module {
+      let linking_info = &graph.linking_infos[entry];
+      if matches!(linking_info.wrap_kind, WrapKind::Cjs) {
+        match output_options.format {
+          output_options::OutputFormat::Esm => {
+            let wrap_ref_name = &self.canonical_names[&linking_info.wrap_ref.unwrap()];
+            return Some(MagicString::new(format!("export default {wrap_ref_name}();\n")));
+          }
+        }
+      }
+    }
+
     let export_items = self.entry_module.map_or_else(
       || {
         self

crates/rolldown/src/bundler/options/normalized_output_options.rs

@@ -1,13 +1,14 @@
 use derivative::Derivative;
 
-use super::file_name_template::FileNameTemplate;
+use super::{file_name_template::FileNameTemplate, output_options::OutputFormat};
 use crate::OutputOptions;
 
 #[derive(Derivative)]
 #[derivative(Debug)]
 pub struct NormalizedOutputOptions {
   pub entry_file_names: FileNameTemplate,
   pub chunk_file_names: FileNameTemplate,
+  pub format: OutputFormat,
 }
 
 impl NormalizedOutputOptions {
@@ -19,6 +20,7 @@ impl NormalizedOutputOptions {
       chunk_file_names: FileNameTemplate::from(
         opts.chunk_file_names.unwrap_or_else(|| "[name]-[hash].js".to_string()),
       ),
+      format: opts.format.unwrap_or(OutputFormat::Esm),
     }
   }
 }

crates/rolldown/src/bundler/options/output_options.rs

@@ -1,9 +1,15 @@
 use derivative::Derivative;
 
+#[derive(Debug)]
+pub enum OutputFormat {
+  Esm,
+}
+
 #[derive(Derivative, Default)]
 #[derivative(Debug)]
 pub struct OutputOptions {
   pub entry_file_names: Option<String>,
   pub chunk_file_names: Option<String>,
   pub dir: Option<String>,
+  pub format: Option<OutputFormat>,
 }

crates/rolldown/tests/esbuild/default/require_main_cache_common_js/artifacts.snap

@@ -24,4 +24,5 @@ var require_entry = __commonJS({
 		console.log('cache:', require.cache);
 	}
 });
+export default require_entry();
 ```

crates/rolldown/tests/esbuild/default/require_main_cache_common_js/test.config.json

@@ -6,5 +6,7 @@
         "import": "entry.js"
       }
     ]
-  }
+  },
+  "_comment": "Build output are executed in esm environment, `require` is not available",
+  "expectExecuted": false
 }

crates/rolldown/tests/esbuild/default/require_with_call_inside_try/artifacts.snap

@@ -22,4 +22,5 @@ var require_entry = __commonJS({
 		}
 	}
 });
+export default require_entry();
 ```

crates/rolldown/tests/fixtures/compat/cjs_entry/_test.mjs

@@ -0,0 +1,4 @@
+import assert from 'assert'
+import main from './dist/main.mjs'
+
+assert.equal(main, 'main')

crates/rolldown/tests/fixtures/compat/cjs_entry/artifacts.snap

@@ -0,0 +1,20 @@
+---
+source: crates/rolldown/tests/common/case.rs
+expression: content
+input_file: crates/rolldown/tests/fixtures/compat/cjs_entry
+---
+# Assets
+
+## main.mjs
+
+```js
+import { __commonJS } from "./_rolldown_runtime.mjs";
+
+// main.js
+var require_main = __commonJS({
+	'main.js'(exports, module) {
+		module.exports = 'main'
+	}
+});
+export default require_main();
+```

crates/rolldown/tests/fixtures/compat/cjs_entry/main.js

@@ -0,0 +1 @@
+module.exports = 'main'

crates/rolldown/tests/fixtures/compat/cjs_entry/test.config.json

@@ -0,0 +1 @@
+{}

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

@@ -62,5 +62,6 @@ pub fn resolve_output_options(opts: OutputOptions) -> napi::Result<rolldown::Out
     entry_file_names: opts.entry_file_names,
     chunk_file_names: opts.chunk_file_names,
     dir: opts.dir,
+    format: None,
   })
 }