feat(aws-cdk): add deprecation warning for legacy exports

Add a prominent warning message when legacy exports from the aws-cdk package are imported. The warning informs users that these exports were never officially supported and will be removed after 2026-03-01, directing them to migrate to the official CDK Toolkit Library.

The warning can be disabled by setting CDK_DISABLE_LEGACY_EXPORT_WARNING=1.

Author: mrgrain

packages/aws-cdk/lib/legacy-exports.ts

@@ -86,3 +86,24 @@ export const {
   data,
   prefix,
 } = legacy;
+
+if (!process.env.CDK_DISABLE_LEGACY_EXPORT_WARNING) {
+  // eslint-disable-next-line no-console
+  console.warn([
+    '',
+    '\x1b[43m\x1b[30m █████████████████████████████████████████████████████████████████████████ \x1b[0m',
+    '\x1b[43m\x1b[30m █                                                                       █ \x1b[0m',
+    '\x1b[43m\x1b[30m █  ⚠ WARNING: You are using LEGACY EXPORTS from the aws-cdk package!    █ \x1b[0m',
+    '\x1b[43m\x1b[30m █                                                                       █ \x1b[0m',
+    '\x1b[43m\x1b[30m █  These exports were never officially supported and will be removed    █ \x1b[0m',
+    '\x1b[43m\x1b[30m █  after 2026-03-01.                                                    █ \x1b[0m',
+    '\x1b[43m\x1b[30m █  Please migrate to using the official CDK Toolkit Library instead:    █ \x1b[0m',
+    '\x1b[43m\x1b[30m █  https://docs.aws.amazon.com/cdk/api/toolkit-lib/                     █ \x1b[0m',
+    '\x1b[43m\x1b[30m █                                                                       █ \x1b[0m',
+    '\x1b[43m\x1b[30m █  For more information: https://github.com/aws/aws-cdk-cli/issues/310  █ \x1b[0m',
+    '\x1b[43m\x1b[30m █  To disable this warning: CDK_DISABLE_LEGACY_EXPORT_WARNING=1         █ \x1b[0m',
+    '\x1b[43m\x1b[30m █                                                                       █ \x1b[0m',
+    '\x1b[43m\x1b[30m █████████████████████████████████████████████████████████████████████████ \x1b[0m',
+    '',
+  ].join('\n'));
+}