Warn about using @babel/runtime@7.0.0-beta.56+ with Meteor 1.7.0.x.

meteor#10126 (comment)

packages/babel-runtime/babel-runtime.js

@@ -4,6 +4,7 @@ try {
   var babelRuntimeVersion = require("@babel/runtime/package.json").version;
 } catch (e) {
   throw new Error([
+    "",
     "The @babel/runtime npm package could not be found in your node_modules ",
     "directory. Please run the following command to install it:",
     "",
@@ -14,6 +15,7 @@ try {
 
 if (parseInt(babelRuntimeVersion, 10) < 6) {
   throw new Error([
+    "",
     "The version of @babel/runtime installed in your node_modules directory ",
     "(" + babelRuntimeVersion + ") is out of date. Please upgrade it by running ",
     "",
@@ -22,4 +24,21 @@ if (parseInt(babelRuntimeVersion, 10) < 6) {
     "in your application directory.",
     ""
   ].join("\n"));
+
+} else if (babelRuntimeVersion.startsWith("7.0.0-beta.")) {
+  var betaVersion = parseInt(babelRuntimeVersion.split(".").pop(), 10);
+  if (betaVersion > 55) {
+    console.warn([
+      "The version of @babel/runtime installed in your node_modules directory ",
+      "(" + babelRuntimeVersion + ") contains a breaking change which was introduced by ",
+      "https://github.com/babel/babel/pull/8266. Please either downgrade by ",
+      "running the following command:",
+      "",
+      "  meteor npm install --save-exact @babel/runtime@7.0.0-beta.55",
+      "",
+      "or update to the latest beta version of Meteor 1.7.1, as explained in ",
+      "this pull request: https://github.com/meteor/meteor/pull/9942.",
+      ""
+    ].join("\n"));
+  }
 }

packages/babel-runtime/package.js

@@ -1,7 +1,7 @@
 Package.describe({
   name: "babel-runtime",
   summary: "Runtime support for output of Babel transpiler",
-  version: '1.2.2',
+  version: '1.2.3',
   documentation: 'README.md'
 });