Better error for export * as ns without the correct plugin

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

@@ -189,6 +189,20 @@ function getExportSpecifierName(
   }
 }
 
+function assertExportSpecifier(
+  path: NodePath,
+): asserts path is NodePath<t.ExportSpecifier> {
+  if (path.isExportSpecifier()) {
+    return;
+  } else if (path.isExportNamespaceSpecifier()) {
+    throw path.buildCodeFrameError(
+      "Export namespace should be first transformed by `@babel/plugin-proposal-export-namespace-from`.",
+    );
+  } else {
+    throw path.buildCodeFrameError("Unexpected export specifier type");
+  }
+}
+
 /**
  * Get metadata about the imports and exports present in this module.
  */
@@ -307,9 +321,7 @@ function getModuleMetadata(
       if (!data.loc) data.loc = child.node.loc;
 
       child.get("specifiers").forEach(spec => {
-        if (!spec.isExportSpecifier()) {
-          throw spec.buildCodeFrameError("Unexpected export specifier type");
-        }
+        assertExportSpecifier(spec);
         const importName = getExportSpecifierName(
           spec.get("local"),
           stringSpecifiers,
@@ -415,8 +427,9 @@ function getLocalExportMetadata(
           child.node.source &&
           child.get("source").isStringLiteral()
         ) {
-          child.node.specifiers.forEach(specifier => {
-            bindingKindLookup.set(specifier.local.name, "block");
+          child.get("specifiers").forEach(spec => {
+            assertExportSpecifier(spec);
+            bindingKindLookup.set(spec.get("local").node.name, "block");
           });
           return;
         }

packages/babel-plugin-transform-modules-commonjs/test/fixtures/noInterop-loose/export-namespace-without-plugin/input.mjs

@@ -0,0 +1,2 @@
+export * as ns from "./foo";
+

packages/babel-plugin-transform-modules-commonjs/test/fixtures/noInterop-loose/export-namespace-without-plugin/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Export namespace should be first transformed by `@babel/plugin-proposal-export-namespace-from`."
+}

packages/babel-plugin-transform-modules-commonjs/test/fixtures/noInterop-loose/options.json

@@ -0,0 +1,5 @@
+{
+  "plugins": [
+    ["transform-modules-commonjs", { "noInterop": true, "loose": true }]
+  ]
+}