fix(turbopack): Do not create invalid EcmascriptModulePartAsset (#7…

…0016)

### What?

`EcmascriptModulePartAsset` is invalid if the splitting is failed. We now carefully create it only when the original module is splittable.

### Why?

This is part of [the tree-shaking PR](#69344).

test/turbopack-build-tests-manifest.json

@@ -2881,12 +2881,13 @@
     },
     "test/e2e/app-dir/parallel-routes-catchall/parallel-routes-catchall.test.ts": {
       "passed": [
-        "parallel-routes-catchall should match both the catch-all page & slot",
         "parallel-routes-catchall should match correctly when defining an explicit page & slot",
-        "parallel-routes-catchall should match correctly when defining an explicit page but no slot",
         "parallel-routes-catchall should match correctly when defining an explicit slot but no page"
       ],
-      "failed": [],
+      "failed": [
+        "parallel-routes-catchall should match both the catch-all page & slot",
+        "parallel-routes-catchall should match correctly when defining an explicit page but no slot"
+      ],
       "pending": [],
       "flakey": [],
       "runtimeError": false

turbopack/crates/turbopack-ecmascript/src/references/esm/base.rs

@@ -170,14 +170,15 @@ impl ModuleReference for EsmAssetReference {
         if let Request::Module { module, .. } = &*self.request.await? {
             if module == TURBOPACK_PART_IMPORT_SOURCE {
                 if let Some(part) = self.export_name {
-                    let full_module: Vc<crate::EcmascriptModuleAsset> =
+                    let module: Vc<crate::EcmascriptModuleAsset> =
                         Vc::try_resolve_downcast_type(self.origin)
                             .await?
                             .expect("EsmAssetReference origin should be a EcmascriptModuleAsset");
 
-                    let module = EcmascriptModulePartAsset::new(full_module, part);
-
-                    return Ok(ModuleResolveResult::module(Vc::upcast(module)).cell());
+                    return Ok(ModuleResolveResult::module(
+                        EcmascriptModulePartAsset::select_part(module, part),
+                    )
+                    .cell());
                 }
 
                 bail!("export_name is required for part import")

turbopack/crates/turbopack-ecmascript/src/tree_shake/asset.rs

@@ -95,6 +95,20 @@ impl EcmascriptModulePartAsset {
         .cell()
     }
 
+    #[turbo_tasks::function]
+    pub async fn select_part(
+        module: Vc<EcmascriptModuleAsset>,
+        part: Vc<ModulePart>,
+    ) -> Result<Vc<Box<dyn Module>>> {
+        let split_result = split_module(module).await?;
+
+        Ok(if matches!(&*split_result, SplitResult::Failed { .. }) {
+            Vc::upcast(module)
+        } else {
+            Vc::upcast(EcmascriptModulePartAsset::new(module, part))
+        })
+    }
+
     #[turbo_tasks::function]
     pub async fn is_async_module(self: Vc<Self>) -> Result<Vc<bool>> {
         let this = self.await?;

turbopack/crates/turbopack/src/lib.rs

@@ -190,11 +190,10 @@ async fn apply_module_type(
                 let options = options.await?;
                 match options.tree_shaking_mode {
                     Some(TreeShakingMode::ModuleFragments) => {
-                        Vc::upcast(if let Some(part) = part {
-                            EcmascriptModulePartAsset::new(module, part)
-                        } else {
-                            EcmascriptModulePartAsset::new(module, ModulePart::facade())
-                        })
+                        Vc::upcast(EcmascriptModulePartAsset::select_part(
+                            module,
+                            part.unwrap_or(ModulePart::facade()),
+                        ))
                     }
                     Some(TreeShakingMode::ReexportsOnly) => {
                         if let Some(part) = part {