ClassDeclaration::set() can't take instances of a class structure with getters among the methods safely

[ajvincent]

Describe the bug

Version: 22.0.0

To Reproduce

import { Project } from "ts-morph";

const project = new Project();
const sourceFile = project.createSourceFile("test.ts", ``);

const classDecl: ClassDeclaration = sourceFile.addClass({ name: "MyClass" });

const outerStructure: ClassDeclarationStructure = {
  kind: StructureKind.Class,
  name: "MyClass",

  methods: [],
};
// ...

class FourthMethod implements MethodDeclarationStructure {
  kind: StructureKind.Method = StructureKind.Method;
  #name = "fourthMethod";
  get name(): string {
    return this.#name;
  }
  set name(newName: string) {
    this.#name = newName;
  }
}
outerStructure.methods?.push(new FourthMethod);

classDecl.set(outerStructure);
console.log(classDecl.print());

Expected behavior

class MyClass {
    fourthMethod {
    }
}

Actual Behavior

ManipulationError: Manipulation error: A syntax error was inserted.

module.ts:11:5 - error TS1068: Unexpected token. A constructor, method, accessor, or property was expected.

Analysis

I tracked this down to a single line in ClassLikeDeclarationBase.ts, in the insertMethods() method:

structures = structures.map(s => ({ ...s }));

Frankly, I don't understand the point of this line. The spread operator, however, will not enumerate over inherited properties (such as the name getter in my sample class above).

Commenting out this line, every existing test in ts-morph still passes. I assume the line itself is a protection against something... but what?

[dsherret]

Without seeing the code, my guess is a naive attempt at cloning in order to not modify the objects the user passed in. Not sure if that actually occurs there though.