Generic components fail to typecheck

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#2,895 8 comments 8 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
30/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
typescript
Domain
compilers

Research direction

Start by reproducing the generic @Component with its @Prop and @Event declarations, then inspect the generated src/components.d.ts where the unresolved Data type is reported. Determine the intended generic behavior for the generated component typings; done means the component compiles and consumer event and result types remain correctly associated with the supplied data type.

Written by the indexing model from the issue text.

Description

Help Wanted Resolution: Refine

Stencil version:

 @stencil/core@2.5.1

I'm submitting a:

[x] bug report
[ ] feature request
[ ] support request => Please do not submit support requests here, use one of these channels: https://stencil-worldwide.herokuapp.com/ or https://forum.ionicframework.com/

Current behavior:

When you try to compile a component that has a generic type based on a property type it fails to compile:

[ ERROR ]  TypeScript: ./src/components.d.ts:152:17
           Cannot find name 'Data'.

    L151:   */
    L152:  "data": Data[];
    L153:  /**

Expected behavior:

The component should compile without issues

Steps to reproduce:

Related code:

If I have a component, say a table-like component that operates on generic types (e.g. emits events of said types), is it possible to make it generic?

@Component(/* ... */)
export class MyTable<Data> {
  @Prop() data: Data[] = [];

  get result(): Data[] {
    // data will be sorted, filtered and sliced
  }

  // Pass the result to parent.
  @Event() update: EventEmitter<Data[]>
}

Now when a consumer sets the data property of <my-table> to say Pokemon you would expect e.g. the update event to reflect that.

type Pokemon = {
  name: string;
  type: string;
  cp: number;
 };

const pokemon: Pokemon = [
  { name: 'Pikachu', type: 'Electric', cp: 500 },
  { name: Magikarp, type: 'Water', cp: 23 },
];

myTable.data = pokemon;
myTable.addEventListener('update', (event) => {
  // `event.detail` and `event.target.result` should be of type `Pokemon[]`
});

Other information:

This is only a minor annoyance as it is trivial to use unknown in this case. But it could offer a nice quality of life if fixed.

Dominant language
TypeScript
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