chore: cannot write file 'aws-iam/index.d.ts' because it would overwrite input file (#36262)

We have been starting to get the above error, because of the style of imports we've been using.

If *inside* `aws-cdk-lib` we use an import of the form:

```ts
import * as iam from 'aws-cdk-lib/aws-iam';
```

Then we add an `index.d.ts` file to the set of inputs, despite there being an `index.ts` right next to it.

This code was being generated by the Grants module generator. Fix it to use a relative import.

----

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

Author: rix0rrr

tools/@aws-cdk/spec2cdk/lib/cdk/aws-cdk-lib.ts

@@ -159,10 +159,14 @@ export class AwsCdkLibBuilder extends LibraryBuilder<AwsCdkLibServiceSubmodule>
 
   private createGrantsModule(moduleName: string, service: Service, grantsConfig: string): LocatedModule<GrantsModule> {
     const filePath = this.pathsFor(moduleName, service).grants;
-    return {
-      module: new GrantsModule(service, this.db, JSON.parse(grantsConfig)),
+    const imports = this.resolveImportPaths(filePath);
+
+    const module = {
+      module: new GrantsModule(service, this.db, JSON.parse(grantsConfig), imports.iam),
       filePath,
     };
+
+    return module;
   }
 
   protected addResourceToSubmodule(submodule: AwsCdkLibServiceSubmodule, resource: Resource, props?: AddServiceProps): void {
@@ -284,6 +288,7 @@ export class AwsCdkLibBuilder extends LibraryBuilder<AwsCdkLibServiceSubmodule>
         coreHelpers: 'aws-cdk-lib/core/lib/helpers-internal',
         coreErrors: 'aws-cdk-lib/core/lib/errors',
         cloudwatch: 'aws-cdk-lib/aws-cloudwatch',
+        iam: 'aws-cdk-lib/aws-iam',
       };
     }
 
@@ -293,6 +298,7 @@ export class AwsCdkLibBuilder extends LibraryBuilder<AwsCdkLibServiceSubmodule>
       coreHelpers: relativeImportPath(sourceModule, 'core/lib/helpers-internal'),
       coreErrors: relativeImportPath(sourceModule, 'core/lib/errors'),
       cloudwatch: relativeImportPath(sourceModule, 'aws-cloudwatch'),
+      iam: relativeImportPath(sourceModule, 'aws-iam'),
     };
   }
 
@@ -337,4 +343,9 @@ export interface ImportPaths {
    * The import name used to import the CloudWatch module
    */
   readonly cloudwatch: string;
+
+  /**
+   * The import name used to import the IAM module
+   */
+  readonly iam: string;
 }

tools/@aws-cdk/spec2cdk/lib/cdk/grants-module.ts

@@ -25,7 +25,12 @@ const $this = $E(expr.this_());
  * repository.
  */
 export class GrantsModule extends Module {
-  public constructor(private readonly service: Service, private readonly db: SpecDatabase, private readonly schema: GrantsFileSchema) {
+  public constructor(
+    private readonly service: Service,
+    private readonly db: SpecDatabase,
+    private readonly schema: GrantsFileSchema,
+    private readonly iamModulePath: string,
+  ) {
     super(`${service.shortName}.grants`);
   }
 
@@ -261,7 +266,7 @@ export class GrantsModule extends Module {
     if (hasContent) {
       new ExternalModule(`aws-cdk-lib/aws-${this.service.shortName}`)
         .import(this, this.service.shortName, { fromLocation: `./${this.service.shortName}.generated` });
-      new ExternalModule('aws-cdk-lib/aws-iam').import(this, 'iam');
+      new ExternalModule('aws-cdk-lib/aws-iam').import(this, 'iam', { fromLocation: this.iamModulePath });
     }
   }
 }

tools/@aws-cdk/spec2cdk/test/grants.test.ts

@@ -29,7 +29,7 @@ test('generates grants for methods with and without key actions', async () => {
     },
   };
   const service = db.lookup('service', 'name', 'equals', 'aws-sns').only();
-  const module = new GrantsModule(service, db, config);
+  const module = new GrantsModule(service, db, config, 'aws-cdk-lib/aws-iam');
 
   const scope = new Module('@aws-cdk/aws-sns');
   const refInterface = new InterfaceType(scope, {