Test Babel compiled using an old version of @babel/core (#11319)

* Test Babel compiled using an old version of @babel/core

This should catch regressions where we use a new helper without a fallback
for older versions, or when we use a new @babel/traverse method.

* Enable the test

.circleci/config.yml

@@ -142,6 +142,14 @@ jobs:
           at: /tmp/verdaccio-workspace
       - run: ./scripts/integration-tests/e2e-babel.sh
 
+  e2e-babel-old-version:
+    executor: node-executor
+    steps:
+      - checkout
+      - attach_workspace:
+          at: /tmp/verdaccio-workspace
+      - run: ./scripts/integration-tests/e2e-babel-old-version.sh
+
   e2e-create-react-app:
     executor: node-executor
     steps:
@@ -191,6 +199,9 @@ workflows:
       - e2e-babel:
           requires:
             - publish-verdaccio
+      - e2e-babel-old-version:
+          requires:
+            - publish-verdaccio
       - e2e-create-react-app:
           requires:
             - publish-verdaccio

scripts/integration-tests/e2e-babel-old-version.sh

@@ -0,0 +1,46 @@
+#!/bin/bash
+
+#==============================================================================#
+#                                  SETUP                                       #
+#==============================================================================#
+
+# Start in scripts/integration-tests/ even if run from root directory
+cd "$(dirname "$0")" || exit
+
+source utils/local-registry.sh
+source utils/cleanup.sh
+
+# Echo every command being executed
+set -x
+
+# Go to the root of the monorepo
+cd ../..
+
+#==============================================================================#
+#                                   TEST                                       #
+#==============================================================================#
+
+startLocalRegistry "$PWD"/scripts/integration-tests/verdaccio-config.yml
+yarn upgrade --scope @babel
+
+# We use @babel/core 7.5.5 instead of 7.0.0 because without babel/babel#10208
+# our @babel/standalone build fails.
+
+node -e "\
+  var pkg = require('./package.json');\
+  pkg.devDependencies['@babel/core'] = '7.5.5';\
+  Object.assign(pkg.resolutions, {\
+    '@babel/core': '7.5.5',\
+    '@babel/helpers': '7.5.5',\
+    '@babel/traverse': '7.0.0'\
+  });\
+  fs.writeFileSync('./package.json', JSON.stringify(pkg, null, 2));\
+"
+
+rm yarn.lock
+make bootstrap
+
+# Test
+make test-ci
+
+cleanup