feat(transformer/decorator): support emitting decorator metadata

[Dunqing]

close: #9186

Implementation

The Implementation port from TypeScript

Example

Input:

class Demo {
  @LogMethod
  public foo(bar: number) {}
  @Prop
  prop: string = "hello";
}

Output:

class Demo {
  foo(bar) {}
  prop = "hello";
}
babelHelpers.decorate([
  LogMethod,
  babelHelpers.decorateParam(0, babelHelpers.decorateMetadata("design:type", Function)),
  babelHelpers.decorateParam(0, babelHelpers.decorateMetadata("design:paramtypes", [Number])),
  babelHelpers.decorateParam(0, babelHelpers.decorateMetadata("design:returntype", void 0))
], Demo.prototype, "foo", null);
babelHelpers.decorate([Prop, babelHelpers.decorateMetadata("design:type", String)], Demo.prototype, "prop", void 0);

Limitations

Compared to TypeScript

We lack a type inference ability that TypeScript has, so we cannot determine the exact type of the TyepReference refers to. See [LegacyDecoratorMetadata::serialize_type_reference_node] does.

For example:
Input:

type Foo = string;
class Cls {
  @dec
  p: Foo = ""
}

TypeScript Output:

class Cls {
  constructor() {
    this.p = "";
  }
}
__decorate([
  dec,
  __metadata("design:type", String) // Infer the type of `Foo` is `String`
], Cls.prototype, "p", void 0);

OXC Output:

var _ref;
class Cls {
    p = "";
}
babelHelpers.decorate([
  dec,
  babelHelpers.decorateMetadata("design:type", typeof (_ref = typeof Foo === "undefined" && Foo) === "function" ? _ref : Object)
],
Cls.prototype, "p", void 0);

Compared to SWC

SWC also has the above limitation, considering that SWC has been adopted in NestJS, so the limitation may not be a problem. In addition, SWC provides additional support for inferring enum members, which we currently do not have. We haven't dived into how NestJS uses it, so we don't know if it matters, thus we may leave it until we receive feedback.

[Dunqing]

• test(transformer/legacy-decorator): add an exec test that verifies it working with reflect-metadata well. #9219
• feat(napi/transform): support enabling emitDecoratorMetadata #9190
• feat(npm/runtime): add decorateMetadata helper function #9189
• feat(transformer/decorator): support emitting decorator metadata #9057 👈 (View in Graphite)
• test(transformer/legacy-decorator): update update-fixtures for emitDecoratorMetadata #9185
• main

---

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[alfaproject]

Yay, looking forward to this!

[codspeed-hq]

CodSpeed Performance Report

Merging #9057 will not alter performance

_{Comparing 02-12-feat_transformer_decorator_support_emitting_decorator_metadata (90ba283) with main (bde4126)}

Summary

✅ 33 untouched benchmarks

[graphite-app]

Merge activity

• Feb 19, 9:04 AM EST: A user added this pull request to the Graphite merge queue.
• Feb 19, 9:11 AM EST: A user merged this pull request with the Graphite merge queue.