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[Bug] Mixin parameters failed to use as Method Parameter types of Inner Classes #50792
Description
🔎 Search Terms
mixin, parameter, class method, type declaration, decorator
🕗 Version & Regression Information
- This is a crash
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about mixin & parameter
⏯ Playground Link
Playground link with relevant code
💻 Code
const register: MethodDecorator = () => { }
const validate: ParameterDecorator = () => { }
function mixin<T>(Model: new (...data: any[]) => T) {
class Trait {
@register
method(@validate input: Model) { }
}
return Trait;
}
class TestModel {
id = 0
}
class TestController extends mixin(TestModel) { }🙁 Actual behavior
Type checking crashed
error TS2749: 'Model' refers to a value, but is being used as a type here. Did you mean 'typeof Model'?
method(@validate input: Model) {
~~~~~
Compiled seems to work
function mixin(Model) {
var _a;
class Trait {
method(input) { }
}
__decorate([
register,
__param(0, validate),
__metadata("design:type", Function),
__metadata("design:paramtypes", [typeof (_a = typeof Model !== "undefined" && Model) === "function" ? _a : Object]),
__metadata("design:returntype", void 0)
], Trait.prototype, "method", null);
return Trait;
}🙂 Expected behavior
Shown sample code works, so that projects with Decorator frameworks will be much simpler, like what my service scaffold does: idea2app/REST-Node-ts#1
Activity
whzx5byb commentedon Sep 15, 2022
The error message is correct.
Modelrefers to a value of a function parameter and you should usetypeofto refer to the type of it.See https://www.typescriptlang.org/docs/handbook/2/typeof-types.html.
TechQuery commentedon Sep 15, 2022
I know that
typeofis the "correct syntax", but if I change it like that, Parameter Decorator will failed to get emited classes:const register: MethodDecorator = () => { } const validate: ParameterDecorator = () => { } function mixin<T>(Model: new (...data: any[]) => T) { class Trait { @register - method(@validate input: Model) { } + method(@validate input: typeof Model) { } } return Trait; } class TestModel { id = 0 } class TestController extends mixin(TestModel) { }function mixin(Model) { var _a; class Trait { method(input) { } } __decorate([ register, __param(0, validate), __metadata("design:type", Function), - __metadata("design:paramtypes", [typeof (_a = typeof Model !== "undefined" && Model) === "function" ? _a : Object]), + __metadata("design:paramtypes", [Object]), __metadata("design:returntype", void 0) ], Trait.prototype, "method", null); return Trait; }whzx5byb commentedon Sep 15, 2022
I think this workaround should work:
function mixin<T>(Model: new (...data: any[]) => T) { + type Model = typeof Model; class Trait { @register method(@validate input: Model) { } } return Trait; }TechQuery commentedon Sep 15, 2022
whzx5byb Thanks your hack code, but I wonder that
classsyntax is both type & value, why should I usetypeofin mixins?TechQuery commentedon Sep 15, 2022
whzx5byb If I use both type & value of classes, your hack code shows a type error in my VS Code 1.71.0:
but
tsccompiling with the sametypescript@4.8.3innode_modulesworks fine...TS playground & GitPod's VS Code 1.69.2 works fine, too...
whzx5byb commentedon Sep 15, 2022
South Drifter (@TechQuery)
A class declaration does create value and type entities but a variable only create the value one. In your case
Modelis just a variable refers to the class, so it doesn't create a type entity.I believe this is a bug, which is similar to #50191 and #50161. I have reported it in #50795.
HerringtonDarkholme commentedon Sep 15, 2022
Minimal reproduction.
compiles to
It looks like the behavior of
typeof Expris not handled properly in decorator metadata.TechQuery commentedon Sep 15, 2022
whzx5byb Thanks your explanation & issue reporting.
When I open my GitPod VS Code again, the same error hints...
Just like #50161 said: sometimes...