chore(neptune-alpha): use typed error (#35960)

### Issue # (if applicable)

Relates #32569

### Reason for this change

Throw typed errors everywhere.

### Description of changes

- add typed error for neptune alpha module

### Describe any new or updated permissions being added

n/a

### Description of how you validated changes

Existing tests. Exemptions granted as this is a refactor of existing code.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

Author: badmintoncryer

packages/@aws-cdk/aws-neptune-alpha/lib/cluster.ts

@@ -3,7 +3,7 @@ import * as ec2 from 'aws-cdk-lib/aws-ec2';
 import * as iam from 'aws-cdk-lib/aws-iam';
 import * as kms from 'aws-cdk-lib/aws-kms';
 import * as logs from 'aws-cdk-lib/aws-logs';
-import { Aws, Duration, IResource, Lazy, RemovalPolicy, Resource, Token } from 'aws-cdk-lib/core';
+import { Aws, Duration, IResource, Lazy, RemovalPolicy, Resource, Token, ValidationError } from 'aws-cdk-lib/core';
 import { Construct } from 'constructs';
 import { Endpoint } from './endpoint';
 import { InstanceType } from './instance';
@@ -540,7 +540,7 @@ export abstract class DatabaseClusterBase extends Resource implements IDatabaseC
 
   public grant(grantee: iam.IGrantable, ...actions: string[]): iam.Grant {
     if (this.enableIamAuthentication === false) {
-      throw new Error('Cannot grant permissions when IAM authentication is disabled');
+      throw new ValidationError('Cannot grant permissions when IAM authentication is disabled', this);
     }
 
     this.enableIamAuthentication = true;
@@ -643,7 +643,7 @@ export class DatabaseCluster extends DatabaseClusterBase implements IDatabaseClu
 
     // Cannot test whether the subnets are in different AZs, but at least we can test the amount.
     if (subnetIds.length < 2) {
-      throw new Error(`Cluster requires at least 2 subnets, got ${subnetIds.length}`);
+      throw new ValidationError(`Cluster requires at least 2 subnets, got ${subnetIds.length}`, this);
     }
 
     this.subnetGroup = props.subnetGroup ?? new SubnetGroup(this, 'Subnets', {
@@ -664,15 +664,15 @@ export class DatabaseCluster extends DatabaseClusterBase implements IDatabaseClu
     const storageEncrypted = props.storageEncrypted ?? true;
 
     if (props.kmsKey && !storageEncrypted) {
-      throw new Error('KMS key supplied but storageEncrypted is false');
+      throw new ValidationError('KMS key supplied but storageEncrypted is false', this);
     }
 
     const deletionProtection = props.deletionProtection ?? (props.removalPolicy === RemovalPolicy.RETAIN ? true : undefined);
 
     this.enableIamAuthentication = props.iamAuthentication;
 
     if (props.instanceType === InstanceType.SERVERLESS && !props.serverlessScalingConfiguration) {
-      throw new Error('You need to specify a serverless scaling configuration with a db.serverless instance type.');
+      throw new ValidationError('You need to specify a serverless scaling configuration with a db.serverless instance type.', this);
     }
 
     this.validateServerlessScalingConfiguration(props.serverlessScalingConfiguration);
@@ -729,7 +729,7 @@ export class DatabaseCluster extends DatabaseClusterBase implements IDatabaseClu
     // Create the instances
     const instanceCount = props.instances ?? DatabaseCluster.DEFAULT_NUM_INSTANCES;
     if (instanceCount < 1) {
-      throw new Error('At least one instance is required');
+      throw new ValidationError('At least one instance is required', this);
     }
 
     for (let i = 0; i < instanceCount; i++) {
@@ -769,14 +769,14 @@ export class DatabaseCluster extends DatabaseClusterBase implements IDatabaseClu
   private validateServerlessScalingConfiguration(serverlessScalingConfiguration?: ServerlessScalingConfiguration) {
     if (!serverlessScalingConfiguration) return;
     if (serverlessScalingConfiguration.minCapacity < 1) {
-      throw new Error(`ServerlessScalingConfiguration minCapacity must be greater or equal than 1, received ${serverlessScalingConfiguration.minCapacity}`);
+      throw new ValidationError(`ServerlessScalingConfiguration minCapacity must be greater or equal than 1, received ${serverlessScalingConfiguration.minCapacity}`, this);
     }
     if (serverlessScalingConfiguration.maxCapacity < 2.5 || serverlessScalingConfiguration.maxCapacity > 128) {
-      throw new Error(`ServerlessScalingConfiguration maxCapacity must be between 2.5 and 128, received ${serverlessScalingConfiguration.maxCapacity}`);
+      throw new ValidationError(`ServerlessScalingConfiguration maxCapacity must be between 2.5 and 128, received ${serverlessScalingConfiguration.maxCapacity}`, this);
     }
     if (serverlessScalingConfiguration.minCapacity >= serverlessScalingConfiguration.maxCapacity) {
-      throw new Error(`ServerlessScalingConfiguration minCapacity ${serverlessScalingConfiguration.minCapacity} ` +
-        `must be less than serverlessScalingConfiguration maxCapacity ${serverlessScalingConfiguration.maxCapacity}`);
+      throw new ValidationError(`ServerlessScalingConfiguration minCapacity ${serverlessScalingConfiguration.minCapacity} ` +
+        `must be less than serverlessScalingConfiguration maxCapacity ${serverlessScalingConfiguration.maxCapacity}`, this);
     }
   }
 }

packages/@aws-cdk/aws-neptune-alpha/lib/instance.ts

@@ -300,7 +300,7 @@ export class InstanceType {
     if (cdk.Token.isUnresolved(instanceType) || instanceType.startsWith('db.')) {
       this._instanceType = instanceType;
     } else {
-      throw new Error(`instance type must start with 'db.'; (got ${instanceType})`);
+      throw new cdk.UnscopedValidationError(`instance type must start with 'db.'; (got ${instanceType})`);
     }
   }
 }