fix(core): exportValue does not work on number attributes (#19818)

Number attributes go through two levels of encoding:

- L1: because of lack of type information, all attributes are assumed to
  be `string`s, so we do `Token.asString(new CfnReference(...))`.
- L2: we recast select attributes to numbers by doing `Token.asNumber()`.

The end result is a Token that looks like:

```ts
asNumber(Intrinsic(asString(CfnReference({ 'Fn::GetAtt': [...] }))))
```

When we do `Tokenization.reverse()` on the number, we only reverse
the *first* encoding one layer, leaving us with an `Intrinsic` instead
of the original `CfnReference`. `exportValue()` then rejects the value
as not being the right type of token.

Solution: before encoding, try to decode the given value so we always
encode the innermost token, and not any of the inbetween ones.

Fixes #19537.


----

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

packages/@aws-cdk/assertions/lib/private/outputs.ts

@@ -20,7 +20,7 @@ export function hasOutput(template: Template, logicalId: string, props: any): st
   }
 
   if (result.closestResult === undefined) {
-    return `No outputs named ${logicalId} found in the template.`;
+    return `No outputs named ${logicalId} found in the template (found: ${Object.keys(section).join(', ')})`;
   }
 
   return [

packages/@aws-cdk/aws-docdb/test/endpoint.test.ts

@@ -1,8 +1,7 @@
 import { Token } from '@aws-cdk/core';
 import { Endpoint } from '../lib';
 
-// A numeric CDK token (see: https://docs.aws.amazon.com/cdk/latest/guide/tokens.html#tokens_number)
-const CDK_NUMERIC_TOKEN = -1.8881545897087626e+289;
+const CDK_NUMERIC_TOKEN = Token.asNumber({ Ref: 'abc' });
 
 describe('Endpoint', () => {
   test('accepts tokens for the port value', () => {

packages/@aws-cdk/aws-rds/test/serverless-cluster.test.ts

@@ -862,6 +862,27 @@ describe('serverless cluster', () => {
       vpcSubnets,
     })).toThrow(/A VPC is required to use vpcSubnets in ServerlessCluster. Please add a VPC or remove vpcSubnets/);
   });
+
+  test('can call exportValue on endpoint.port', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'VPC');
+    const cluster = new ServerlessCluster(stack, 'Database', {
+      engine: DatabaseClusterEngine.AURORA_MYSQL,
+      credentials: { username: 'admin' },
+      vpc,
+    });
+
+    // WHEN
+    stack.exportValue(cluster.clusterEndpoint.port);
+
+    // THEN
+    const template = Template.fromStack(stack);
+    template.hasOutput('ExportsOutputFnGetAttDatabaseB269D8BBEndpointPort3ACB3F51', {
+      Value: { 'Fn::GetAtt': ['DatabaseB269D8BB', 'Endpoint.Port'] },
+      Export: { Name: 'Default:ExportsOutputFnGetAttDatabaseB269D8BBEndpointPort3ACB3F51' },
+    });
+  });
 });
 
 function testStack(app?: cdk.App, id?: string): cdk.Stack {

packages/@aws-cdk/core/lib/token.ts

@@ -99,6 +99,10 @@ export class Token {
    * Return a resolvable representation of the given value
    */
   public static asAny(value: any): IResolvable {
+    // First, reverse any encoding that was already done (so we end up with an IResolvable
+    // if it was a token).
+    value = Tokenization.reverse(value) ?? value;
+    // Then,  either return the IResolvable we resolved to, or wrap in an Intrinsic
     return isResolvableObject(value) ? value : new Intrinsic(value);
   }
 

packages/@aws-cdk/core/test/tokens.test.ts

@@ -523,6 +523,21 @@ describe('tokens', () => {
       expect(resolved).toEqual({ value: 123 });
     });
 
+    test('Tokens are still reversible after having been encoded multiple times', () => {
+      // GIVEN
+      const original = new Intrinsic(123);
+
+      // WHEN
+      let x: any = original;
+      x = Token.asString(x);
+      x = Token.asNumber(x);
+      x = Token.asList(x);
+      x = Token.asString(x);
+
+      // THEN
+      expect(Tokenization.reverse(x)).toBe(original);
+    });
+
     test('regex detects all stringifications of encoded tokens', () => {
       expect(stringContainsNumberTokens(`${createTokenDouble(0)}`)).toBeTruthy();
       expect(stringContainsNumberTokens(`${createTokenDouble(Math.pow(2, 48) - 1)}`)).toBeTruthy(); // MAX_ENCODABLE_INTEGER