fix(cli): hotswap doesn't update SSM parameter environment variables …

…properly (#26382)

Closes #25387
Closes #25483  

The actual value for a CfnParameter backed by a SSM parameter is returned via `ResolvedValue` (and only for SSM parameters, [doc](https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_Parameter.html#API_Parameter_Contents)). We use the field from DescirbeStacks API response to populate `stackParams`, instead of `ParameterValue`, which is just a parameter's name. 

As far as I checked it is not a breaking change. The `parameter` field is not a public API, and internally the values of SSM parameters are only used for hotswap.

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*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

@@ -156,7 +156,7 @@ export class CloudFormationStack {
     if (!this.exists) { return {}; }
     const ret: Record<string, string> = {};
     for (const param of this.stack!.Parameters ?? []) {
-      ret[param.ParameterKey!] = param.ParameterValue!;
+      ret[param.ParameterKey!] = param.ResolvedValue ?? param.ParameterValue!;
     }
     return ret;
   }

packages/aws-cdk/test/api/deploy-stack.test.ts

@@ -149,6 +149,36 @@ test('correctly passes CFN parameters when hotswapping', async () => {
   expect(tryHotswapDeployment).toHaveBeenCalledWith(expect.anything(), { A: 'A-value', B: 'B=value' }, expect.anything(), expect.anything(), HotswapMode.FALL_BACK);
 });
 
+test('correctly passes SSM parameters when hotswapping', async () => {
+  // GIVEN
+  givenStackExists({
+    Parameters: [
+      { ParameterKey: 'SomeParameter', ParameterValue: 'ParameterName', ResolvedValue: 'SomeValue' },
+    ],
+  });
+
+  // WHEN
+  await deployStack({
+    ...standardDeployStackArguments(),
+    stack: testStack({
+      stackName: 'stack',
+      template: {
+        Parameters: {
+          SomeParameter: {
+            Type: 'AWS::SSM::Parameter::Value<String>',
+            Default: 'ParameterName',
+          },
+        },
+      },
+    }),
+    hotswap: HotswapMode.FALL_BACK,
+    usePreviousParameters: true,
+  });
+
+  // THEN
+  expect(tryHotswapDeployment).toHaveBeenCalledWith(expect.anything(), { SomeParameter: 'SomeValue' }, expect.anything(), expect.anything(), HotswapMode.FALL_BACK);
+});
+
 test('call CreateStack when method=direct and the stack doesnt exist yet', async () => {
   // WHEN
   await deployStack({