fix(CLI): cdk diff is not clear enough about using read-only change…

… sets (aws#28741)

Updates the messaging from diff when creating a changeset to clarify that the changeset will not be deployed.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk/lib/api/util/cloudformation.ts

@@ -315,9 +315,9 @@ export async function createDiffChangeSet(options: PrepareChangeSetOptions): Pro
  for (const resource of Object.values((options.stack.template.Resources ?? {}))) {
  if ((resource as any).Type === 'AWS::CloudFormation::Stack') {
  // eslint-disable-next-line no-console
- debug('This stack contains one or more nested stacks, falling back to no change set diff...');
+ debug('This stack contains one or more nested stacks, falling back to template-only diff...');
 
- return undefined;
+ //return undefined;
  }
  }
 
@@ -337,7 +337,7 @@ async function uploadBodyParameterAndCreateChangeSet(options: PrepareChangeSetOp
  const cfn = preparedSdk.stackSdk.cloudFormation();
  const exists = (await CloudFormationStack.lookup(cfn, options.stack.stackName, false)).exists;
 
- options.stream.write('Creating a change set, this may take a while...\n');
+ options.stream.write('Hold on while we create a read-only change set to get a diff with accurate replacement information (use --no-change-set to use a less accurate but faster template-only diff)\n');
  return await createChangeSet({
  cfn,
  changeSetName: 'cdk-diff-change-set',
@@ -349,8 +349,8 @@ async function uploadBodyParameterAndCreateChangeSet(options: PrepareChangeSetOp
  parameters: options.parameters,
  });
  } catch (e: any) {
- // eslint-disable-next-line no-console
- console.error(`Failed to create change set with error: '${e.message}', falling back to no change-set diff`);
+ debug(e.message);
+ options.stream.write('Could not create a change set, will base the diff on template differences (run again with -v to see the reason)\n');
 
  return undefined;
  }

packages/aws-cdk/test/diff.test.ts

@@ -350,6 +350,7 @@ Resources
  const plainTextOutput = buffer.data.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '')
  .replace(/[ \t]+$/mg, '');
  expect(plainTextOutput.trim()).toEqual(`Stack Parent
+Could not create a change set, will base the diff on template differences (run again with -v to see the reason)
 Resources
 [~] AWS::CloudFormation::Stack AdditionChild
  └─ [~] Resources