add a debug assert that EsmAssetReference never resolves to more than one result

Author: lukesandberg

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

@@ -459,9 +459,16 @@ impl ModuleReference for EsmAssetReference {
             Some(self.issue_source),
         )
         .await?;
+        let modules = result.primary_modules().await?;
+        debug_assert!(
+            modules.len() <= 1,
+            "EsmAssetReference request {request} resolved to {num} results",
+            request = &self.request,
+            num = modules.len()
+        );
 
         if let Some(ModulePart::Export(export_name)) = &self.export_name {
-            for &module in result.primary_modules().await? {
+            for &module in modules {
                 if let Some(module) = ResolvedVc::try_downcast(module)
                     && *is_export_missing(*module, export_name.clone()).await?
                 {