Move meteorBabelHelpers to modules package, and restrict to legacy bundle.

packages/babel-runtime/babel-runtime.js

@@ -1,5 +1,3 @@
-exports.meteorBabelHelpers = require("meteor-babel-helpers");
-
 try {
   var babelRuntimeVersion = require("@babel/runtime/package.json").version;
 } catch (e) {

packages/babel-runtime/package.js

@@ -1,16 +1,11 @@
 Package.describe({
   name: "babel-runtime",
   summary: "Runtime support for output of Babel transpiler",
-  version: '1.3.0',
+  version: '1.4.0',
   documentation: 'README.md'
 });
 
-Npm.depends({
-  "meteor-babel-helpers": "0.0.3"
-});
-
 Package.onUse(function (api) {
   api.use("modules");
   api.mainModule("babel-runtime.js");
-  api.export("meteorBabelHelpers");
 });

packages/ecmascript/runtime-tests.js

@@ -322,8 +322,10 @@ Tinytest.add("ecmascript - runtime - destructuring", (test) => {
 
 Tinytest.addAsync("ecmascript - runtime - misc support", (test, done) => {
   // Verify that the runtime was installed.
-  test.equal(typeof meteorBabelHelpers, "object");
-  test.equal(typeof meteorBabelHelpers.sanitizeForInObject, "function");
+  if (Meteor.isLegacy) {
+    test.equal(typeof meteorBabelHelpers, "object");
+    test.equal(typeof meteorBabelHelpers.sanitizeForInObject, "function");
+  }
 
   class Base {
     constructor(...args) {

packages/modules/legacy.js

@@ -0,0 +1,4 @@
+// The meteor-babel/plugins/sanitize-for-in-objects plugin generates code
+// that uses meteorBabelHelpers.sanitizeForInObject, but only when
+// compiling code for the web.browser.legacy bundle. See #10595.
+meteorBabelHelpers = require("meteor-babel-helpers");

packages/modules/package.js

@@ -6,12 +6,21 @@ Package.describe({
 });
 
 Npm.depends({
-  reify: "0.20.6"
+  reify: "0.20.6",
+  "meteor-babel-helpers": "0.0.3"
 });
 
 Package.onUse(function(api) {
   api.use("modules-runtime");
   api.mainModule("client.js", "client");
   api.mainModule("server.js", "server");
   api.export("meteorInstall");
+
+  // When compiling legacy code, the babel-compiler and meteor-babel
+  // packages assume meteorBabelHelpers.sanitizeForInObject is defined.
+  // Since the modules package is responsible for code from node_modules,
+  // it must also be responsible for exposing this runtime helper, but
+  // only in the legacy bundle.
+  api.addFiles("legacy.js", "legacy");
+  api.export("meteorBabelHelpers", "legacy");
 });