Use strict namespace behavior for mjs files. (#7545)

packages/babel-helper-module-transforms/src/index.js

@@ -22,7 +22,16 @@ export { hasExports, isSideEffectImport, isModule };
  */
 export function rewriteModuleStatementsAndPrepareHeader(
   path: NodePath,
-  { exportName, strict, allowTopLevelThis, strictMode, loose, noInterop, lazy },
+  {
+    exportName,
+    strict,
+    allowTopLevelThis,
+    strictMode,
+    loose,
+    noInterop,
+    lazy,
+    esNamespaceOnly,
+  },
 ) {
   assert(isModule(path), "Cannot process module statements in a script");
   path.node.sourceType = "script";
@@ -31,6 +40,7 @@ export function rewriteModuleStatementsAndPrepareHeader(
     noInterop,
     loose,
     lazy,
+    esNamespaceOnly,
   });
 
   if (!allowTopLevelThis) {

packages/babel-helper-module-transforms/src/normalize-and-load-metadata.js

@@ -86,7 +86,12 @@ export function isSideEffectImport(source: SourceModuleMetadata) {
 export default function normalizeModuleAndLoadMetadata(
   programPath: NodePath,
   exportName?: string,
-  { noInterop = false, loose = false, lazy = false } = {},
+  {
+    noInterop = false,
+    loose = false,
+    lazy = false,
+    esNamespaceOnly = false,
+  } = {},
 ): ModuleMetadata {
   if (!exportName) {
     exportName = programPath.scope.generateUidIdentifier("exports").name;
@@ -107,6 +112,16 @@ export default function normalizeModuleAndLoadMetadata(
     }
 
     if (noInterop) metadata.interop = "none";
+    else if (esNamespaceOnly) {
+      // Both the default and namespace interops pass through __esModule
+      // objects, but the namespace interop is used to enable Babel's
+      // destructuring-like interop behavior for normal CommonJS.
+      // Since some tooling has started to remove that behavior, we expose
+      // it as the `esNamespace` option.
+      if (metadata.interop === "namespace") {
+        metadata.interop = "default";
+      }
+    }
   }
 
   return {