Incorrect reference `this` in static context with `experimentalDecorators` enabled

🔎 Search Terms

"static this", "experimental decorators"

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about static

⏯ Playground Link

https://www.typescriptlang.org/play/?experimentalDecorators=true&target=7&ts=5.9.3&emitDecoratorMetadata=true#code/GYVwdgxgLglg9mABAEQKYTgJwIZS4gCim0wHNUoAuRAMXGnjABpEBrVAT2oGcpMYwpRAB9E4ACapgA1OJYDJAD2pgQAWwBGqTAEpEAbwC+AKGMQANtm7dEAWQ4BhADJWb+44kS9cMCIkyo2OII5hxexLAQACoAFjDcAEpSiAC8iFBx3ADcHogYYLyYINBYBAACaBg4eJiIwHBwKupaugYmJkA

💻 Code

function Decorator (target: Function, key: string | undefined, index: number) {}

class MyClass {
  static readonly staticThisRef = this;
  constructor(@Decorator foo: number) {}
}

🙁 Actual behavior

MyClass.staticThisRef = (void 0);

🙂 Expected behavior

staticThisRef points to the class.

Additional information about the issue

Enabling or disabling experimentalDecorators fixes the issue.

With experimentalDecorators:

let MyClass = class MyClass {
    constructor(foo) { }
};
MyClass.staticThisRef = (void 0);
MyClass = __decorate([
    __param(0, Decorator)
], MyClass);

Without experimentalDecorators:

class MyClass {
    constructor(foo) { }
}
_a = MyClass;
MyCLass.staticThisRef = _a;

However only experimental decorators support decorating parameters.

Also TypeScript compiler behavior here is different from esbuild with experimentalDecorators feature enabled:

https://esbuild.github.io/try/#dAAwLjI3LjMALS1sb2FkZXI9dHMgIi0tdHNjb25maWctcmF3PXtcImNvbXBpbGVyT3B0aW9uc1wiOntcImV4cGVyaW1lbnRhbERlY29yYXRvcnNcIjp0cnVlfX0iAGZ1bmN0aW9uIERlY29yYXRvciAodGFyZ2V0OiBGdW5jdGlvbiwga2V5OiBzdHJpbmcgfCB1bmRlZmluZWQsIGluZGV4OiBudW1iZXIpIHt9CgpjbGFzcyBNeUNMYXNzIHsKICBzdGF0aWMgcmVhZG9ubHkgc3RhdGljVGhpc1JlZiA9IHRoaXM7CiAgY29uc3RydWN0b3IoQERlY29yYXRvciBmb286IG51bWJlcikge30KfQ

提供されている TypeScript Playground の例から始め、experimentalDecorators を有効にした場合と無効にした場合の出力を比較します。デコレートされたコンストラクターパラメーターを持つクラスに対して、static な this 参照を出力するコンパイラーパスを調査します。experimental-decorator の出力によって staticThisRef が MyClass を指し、パラメーターのデコレーションのサポートが維持されれば完了です。