revert: prevent changeset diff for non-deployed stacks (#29485)

reverts #29394, which prevented changeset creation during `cdk diff` if
a stack did not exist. The lookup of the stack to check its existence is
failing for customers that have CI/CD that won't assume the deploy role
when running CDK diff.

Long-term fix: delete the stack if it didn't exist before we created the
changeset, but wait for its state to reach `DELETE_COMPLETE` to avoid
problems with subsequent commands.

Preserves changes from #29172

----

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

packages/@aws-cdk/cloudformation-diff/lib/diff-template.ts

@@ -37,7 +37,6 @@ const DIFF_HANDLERS: HandlerRegistry = {
  * @param currentTemplate the current state of the stack.
  * @param newTemplate     the target state of the stack.
  * @param changeSet       the change set for this stack.
- * @param isImport        if the stack is importing resources (a migrate stack).
  *
  * @returns a +types.TemplateDiff+ object that represents the changes that will happen if
  *      a stack which current state is described by +currentTemplate+ is updated with
@@ -47,7 +46,6 @@ export function fullDiff(
   currentTemplate: { [key: string]: any },
   newTemplate: { [key: string]: any },
   changeSet?: CloudFormation.DescribeChangeSetOutput,
-  isImport?: boolean,
 ): types.TemplateDiff {
 
   normalize(currentTemplate);
@@ -57,9 +55,6 @@ export function fullDiff(
     filterFalsePositives(theDiff, changeSet);
     addImportInformation(theDiff, changeSet);
   }
-  if (isImport) {
-    addImportInformation(theDiff);
-  }
 
   return theDiff;
 }
@@ -214,25 +209,13 @@ function deepCopy(x: any): any {
   return x;
 }
 
-/**
- * Sets import flag to true for resource imports.
- * When the changeset parameter is not set, the stack is a new migrate stack,
- * so all resource changes are imports.
- */
-function addImportInformation(diff: types.TemplateDiff, changeSet?: CloudFormation.DescribeChangeSetOutput) {
-  if (changeSet) {
-    const imports = findResourceImports(changeSet);
-    diff.resources.forEachDifference((logicalId: string, change: types.ResourceDifference) => {
-      if (imports.includes(logicalId)) {
-        change.isImport = true;
-      }
-    });
-  } else {
-    diff.resources.forEachDifference((logicalId: string, change: types.ResourceDifference) => {
-      logicalId; // dont know how to get past warning that this variable is not used.
+function addImportInformation(diff: types.TemplateDiff, changeSet: CloudFormation.DescribeChangeSetOutput) {
+  const imports = findResourceImports(changeSet);
+  diff.resources.forEachDifference((logicalId: string, change: types.ResourceDifference) => {
+    if (imports.includes(logicalId)) {
       change.isImport = true;
-    });
-  }
+    }
+  });
 }
 
 function filterFalsePositives(diff: types.TemplateDiff, changeSet: CloudFormation.DescribeChangeSetOutput) {

packages/aws-cdk/lib/cdk-toolkit.ts

@@ -136,14 +136,7 @@ export class CdkToolkit {
         throw new Error(`There is no file at ${options.templatePath}`);
       }
 
-      const stackExistsOptions = {
-        stack: stacks.firstStack,
-        deployName: stacks.firstStack.stackName,
-      };
-
-      const stackExists = await this.props.deployments.stackExists(stackExistsOptions);
-
-      const changeSet = (stackExists && options.changeSet) ? await createDiffChangeSet({
+      const changeSet = options.changeSet ? await createDiffChangeSet({
         stack: stacks.firstStack,
         uuid: uuid.v4(),
         willExecute: false,
@@ -175,23 +168,13 @@ export class CdkToolkit {
           removeNonImportResources(stack);
         }
 
-        const stackExistsOptions = {
-          stack,
-          deployName: stack.stackName,
-        };
-
-        const stackExists = await this.props.deployments.stackExists(stackExistsOptions);
-
-        // if the stack does not already exist, do not do a changeset
-        // this prevents race conditions between deleting the dummy changeset stack and deploying the real changeset stack
-        // migrate stacks that import resources will not previously exist and default to old diff logic
-        const changeSet = (stackExists && options.changeSet) ? await createDiffChangeSet({
+        const changeSet = options.changeSet ? await createDiffChangeSet({
           stack,
           uuid: uuid.v4(),
           deployments: this.props.deployments,
           willExecute: false,
           sdkProvider: this.props.sdkProvider,
-          parameters: Object.assign({}, parameterMap['*'], parameterMap[stacks.firstStack.stackName]), // should this be stack?
+          parameters: Object.assign({}, parameterMap['*'], parameterMap[stacks.firstStack.stackName]),
           resourcesToImport,
           stream,
         }) : undefined;
@@ -200,11 +183,10 @@ export class CdkToolkit {
           stream.write('Parameters and rules created during migration do not affect resource configuration.\n');
         }
 
-        // pass a boolean to print if the stack is a migrate stack in order to set all resource diffs to import
         const stackCount =
         options.securityOnly
           ? (numberFromBool(printSecurityDiff(currentTemplate, stack, RequireApproval.Broadening, changeSet)))
-          : (printStackDiff(currentTemplate, stack, strict, contextLines, quiet, changeSet, stream, nestedStacks, !!resourcesToImport));
+          : (printStackDiff(currentTemplate, stack, strict, contextLines, quiet, changeSet, stream, nestedStacks));
 
         diffs += stackCount;
       }

packages/aws-cdk/lib/diff.ts

@@ -26,10 +26,9 @@ export function printStackDiff(
   quiet: boolean,
   changeSet?: CloudFormation.DescribeChangeSetOutput,
   stream: cfnDiff.FormatStream = process.stderr,
-  nestedStackTemplates?: { [nestedStackLogicalId: string]: NestedStackTemplates },
-  isImport?: boolean): number {
+  nestedStackTemplates?: { [nestedStackLogicalId: string]: NestedStackTemplates }): number {
 
-  let diff = cfnDiff.fullDiff(oldTemplate, newTemplate.template, changeSet, isImport);
+  let diff = cfnDiff.fullDiff(oldTemplate, newTemplate.template, changeSet);
 
   // detect and filter out mangled characters from the diff
   let filteredChangesCount = 0;