fix(core): CfnParameter of Number type cannot be used as a string (#1…

…0422)

CloudFormation allows for parameters of type 'Number' to be referenced,
using the 'Ref' keyword, into properties that are of type 'String'.

This will let customers now use CloudFormation maximum and minimum
constraints on the number parameter type, and still use the resulting
value in a property of string type.

fixes #10228


----

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

packages/@aws-cdk/core/lib/cfn-parameter.ts

@@ -289,8 +289,8 @@ export class CfnParameter extends CfnElement {
    * The parameter value, if it represents a string.
    */
   public get valueAsString(): string {
-    if (!isStringType(this.type)) {
-      throw new Error(`Parameter type (${this.type}) is not a string type`);
+    if (!isStringType(this.type) && !isNumberType(this.type)) {
+      throw new Error(`Parameter type (${this.type}) is not a string or number type`);
     }
     return Token.asString(this.value);
   }

packages/@aws-cdk/core/test/test.cfn-parameter.ts

@@ -0,0 +1,32 @@
+import { Test } from 'nodeunit';
+import { CfnParameter, Stack } from '../lib';
+
+export = {
+  'valueAsString supports both string and number types'(test: Test) {
+    // GIVEN
+    const stack = new Stack();
+    const numberParam = new CfnParameter(stack, 'numberParam', { type: 'Number', default: 10 });
+    const stringParam = new CfnParameter(stack, 'stringParam', { type: 'String', default: 'a-default' });
+
+    // WHEN
+    const numVal = numberParam.valueAsString;
+    const strVal = stringParam.valueAsString;
+
+    // THEN
+    test.deepEqual(stack.resolve(numVal), { Ref: 'numberParam' });
+    test.deepEqual(stack.resolve(strVal), { Ref: 'stringParam' });
+
+    test.done();
+  },
+
+  'valueAsString fails for unsupported types'(test: Test) {
+    // GIVEN
+    const stack = new Stack();
+    const listParam = new CfnParameter(stack, 'listParam', { type: 'List', default: 10 });
+
+    // WHEN - THEN
+    test.throws(() => listParam.valueAsList, /Parameter type \(List\)/);
+
+    test.done();
+  },
+}