Ts-morph: Shorthand ambient modules do not have a body

[velut]

Describe the bug

Typescript allows declaring ambient modules without a body, known as shorthand ambient modules.

// index.d.ts

declare module "foo";

Operations accessing the body of this kind of modules fail with the error Bodied node should have a body..

Version: 9.1.0
Typescript version: 4.1.3

To Reproduce

import { Node, Project, ts } from "ts-morph";

// Logs `4.1.3`
console.log(ts.version);

// Create ambient file `index.d.ts` containing a shorthand ambient module
const project = new Project();
const sourceFile = project.createSourceFile(
  "index.d.ts",
  `declare module "foo";`
);

// Module name is "foo" with quotes included
const fooModule = sourceFile.getNamespaceOrThrow('"foo"');

// Another way to access module "foo" as a simple `Node` and not a `NamespaceDeclaration`
// const fooModule = project.getAmbientModuleOrThrow('"foo"').getDeclarations()[0];

// Logs `declare module "foo";`
console.log(fooModule.getFullText());

// Throws `Bodied node should have a body.`
if (Node.isBodiedNode(fooModule)) {
  fooModule.getBody();
}

Expected behavior

Shorthand ambient modules should not be considered bodied modules.

Workaround

A possible workaround to identify shorthand ambient modules consists in checking if they have any ModuleBlock descendants.

const isShorthandAmbientModule = module.getDescendantsOfKind(SyntaxKind.ModuleBlock).length === 0

[dsherret]

Yes, this is a bug. I think probably in this case it shouldn't show up for any getNamespace methods either.

export interface NamespaceDeclaration extends ModuleDeclaration {
    readonly name: Identifier;
    readonly body: NamespaceBody;
}

export interface ModuleDeclaration extends DeclarationStatement, JSDocContainer {
    readonly kind: SyntaxKind.ModuleDeclaration;
    readonly parent: ModuleBody | SourceFile;
    readonly name: ModuleName;
    readonly body?: ModuleBody | JSDocNamespaceDeclaration;
}

Given the compiler does the above, I think probably a ModuleDeclaration node should be introduced for these.

[dsherret]

Just looking into this now... ts-morph doesn't represent ambient module declarations acurately. Also, I discovered there is an internal AmbientModuleDeclaration type in the compiler API:

export interface AmbientModuleDeclaration extends ModuleDeclaration {
    readonly body?: ModuleBlock;
}

That said, these types seem to be just for assertions.

I've been thinking about this more and ts-morph relies heavily on having a mapping from syntax kind to wrapped node. Given ModuleDeclaration, NamespaceDeclaration and AmbientModuleDeclaration all have the same kind, I'm thinking to rename NamespaceDeclaration to ModuleDeclaration and then ModuleDeclaration will handle all of these. It would have been nice if the compiler api had structured these a little nicer, but it is what it is.

I'll make these updates before the next TS major release on Feb 23rd.