transpileModule does not elide type only "import equals" under emitDecoratorMetadata

[frigus02]

🔎 Search Terms

isolatedModules import alias

🕗 Version & Regression Information

• This is the behavior in every version I tried: v5.1.1, v5.2.2, v5.3.0-dev.20230830

⏯ Playground Link

https://www.typescriptlang.org/play?importHelpers=true&experimentalDecorators=true&emitDecoratorMetadata=true&isolatedModules=true&noResolve=true&ts=5.3.0-dev.20230830#code/JYWwDg9gTgLgBAbwJIDsYFMoDMCGBjdAXziyghDgHIA6AehgE8x0BnSgbgChPRJY4AcqwwATVBmz50cALxxxmXAWpCWohZIJdOI9HgA2OKNLwQUa+SjABXGAC44OFA23oAHn3gGcLFnABiEBCInHBhcAACqDbwYGRgAIQOqupoilJchEA

💻 Code

import {Interface} from './types';

import NestedInterface = Interface.NestedInterface;

declare const Input: any;

export class Foo {
 @Input prop!: NestedInterface;
}

🙁 Actual behavior

var _a;
import { __decorate, __metadata } from "tslib";
import { Interface } from './types';
var NestedInterface = Interface.NestedInterface; // <-- this can throw at runtime
export class Foo {
}
__decorate([
 Input,
 __metadata("design:type", typeof (_a = typeof NestedInterface !== "undefined" && NestedInterface) === "function" ? _a : Object)
], Foo.prototype, "prop", void 0);

🙂 Expected behavior

Either of the following would work, I think:

• Make this pattern an error, possibly requiring sth like import type NestedInterface = Interface.NestedInterface;
• Elide import equals
• Emit var NestedInterface = ... using a runtime check, similarly as in the decorator metadata code

Additional information about the issue

Very similar to #49450