feat(lambda): validate function description length (#20476)

closes #20475.

----

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packages/@aws-cdk/aws-lambda/lib/function.ts

@@ -668,6 +668,12 @@ export class Function extends FunctionBase {
       }
     }
 
+    if (props.description && !Token.isUnresolved(props.description)) {
+      if (props.description.length > 256) {
+        throw new Error(`Function description can not be longer than 256 characters but has ${props.description.length} characters.`);
+      }
+    }
+
     const managedPolicies = new Array<iam.IManagedPolicy>();
 
     // the arn is in the form of - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

packages/@aws-cdk/aws-lambda/test/function.test.ts

@@ -2648,6 +2648,31 @@ describe('function', () => {
     }).not.toThrow();
   });
 
+  test('Error when function description is longer than 256 chars', () => {
+    const stack = new cdk.Stack();
+    expect(() => new lambda.Function(stack, 'MyFunction', {
+      code: lambda.Code.fromInline('foo'),
+      runtime: lambda.Runtime.NODEJS_14_X,
+      handler: 'index.handler',
+      description: 'a'.repeat(257),
+    })).toThrow(/Function description can not be longer than 256 characters/);
+  });
+
+  test('No error when function name is Tokenized and Unresolved', () => {
+    const stack = new cdk.Stack();
+    expect(() => {
+      const realFunctionDescription = 'a'.repeat(257);
+      const tokenizedFunctionDescription = cdk.Token.asString(new cdk.Intrinsic(realFunctionDescription));
+
+      new lambda.Function(stack, 'foo', {
+        code: new lambda.InlineCode('foo'),
+        handler: 'index.handler',
+        runtime: lambda.Runtime.NODEJS_14_X,
+        description: tokenizedFunctionDescription,
+      });
+    }).not.toThrow();
+  });
+
   describe('FunctionUrl', () => {
     test('addFunctionUrl creates a function url with default options', () => {
     // GIVEN