fix(cloudformation): cannot reference resource attributes with "." in nested stacks (#4684)

When rendering the "GetAtt" to reference an auto-generated nested stack output
we did not use the actual `output.logicalId`, which can differ from the `id` passed
into the output (for example, periods are omitted since they are not supported in logical IDs).

This change uses the actual logical ID, but then requires that for sibling-references
we resolve this string since it's used for the logical ID of the parameter. Yeah, tricky.

Author: Elad Ben-Israel

packages/@aws-cdk/aws-cloudformation/lib/nested-stack.ts

@@ -149,7 +149,8 @@ export class NestedStack extends Stack {
     // the nested stack references a resource from the parent stack:
     // we pass it through a as a cloudformation parameter
     if (targetStack === sourceStack.parentStack) {
-      const paramId = `reference-to-${reference.target.node.uniqueId}.${reference.displayName}`;
+      // we call "this.resolve" to ensure that tokens do not creep in (for example, if the reference display name includes tokens)
+      const paramId = this.resolve(`reference-to-${reference.target.node.uniqueId}.${reference.displayName}`);
       let param = this.node.tryFindChild(paramId) as CfnParameter;
       if (!param) {
         param = new CfnParameter(this, paramId, { type: 'String' });
@@ -195,7 +196,7 @@ export class NestedStack extends Stack {
       output = new CfnOutput(this, outputId, { value: Token.asString(reference) });
     }
 
-    return this.resource.getAtt(`Outputs.${outputId}`);
+    return this.resource.getAtt(`Outputs.${output.logicalId}`);
   }
 
   private contextualAttribute(innerValue: string, outerValue: string) {

packages/@aws-cdk/aws-cloudformation/test/test.nested-stack.ts

@@ -827,6 +827,50 @@ export = {
         data: 'bar'
       }
     ]);
+    test.done();
+  },
+
+  'referencing attributes with period across stacks'(test: Test) {
+    // GIVEN
+    const parent = new Stack();
+    const nested = new NestedStack(parent, 'nested');
+    const consumed = new CfnResource(nested, 'resource-in-nested', { type: 'CONSUMED' });
+
+    // WHEN
+    new CfnResource(parent, 'resource-in-parent', {
+      type: 'CONSUMER',
+      properties: {
+        ConsumedAttribute: consumed.getAtt('Consumed.Attribute')
+      }
+    });
+
+    // THEN
+    expect(nested).toMatch({
+      Resources: {
+        resourceinnested: {
+          Type: "CONSUMED"
+        }
+      },
+      Outputs: {
+        nestedresourceinnested59B1F01CConsumedAttribute: {
+          Value: {
+            "Fn::GetAtt": [
+              "resourceinnested",
+              "Consumed.Attribute"
+            ]
+          }
+        }
+      }
+    });
+    expect(parent).to(haveResource('CONSUMER', {
+      ConsumedAttribute: {
+        "Fn::GetAtt": [
+          "nestedNestedStacknestedNestedStackResource3DD143BF",
+          "Outputs.nestedresourceinnested59B1F01CConsumedAttribute"
+        ]
+      }
+    }));
+
     test.done();
   }
 };