fix(declarations): use correct TypeScript JSX typings

[maxpatiiuk]

What is the current behavior?

Fix incorrect JSX typings, as described in great detail in #5306

GitHub Issue Number: #5306

What is the new behavior?

TypeScript compiler is able to resolve Stencil's JSX typings correctly, thus working well with third-party tools that use TypeScript compiler types

Documentation

Described in great detail in #5306

Does this introduce a breaking change?

• Yes
• No

Testing

The error affects tools that use the TypeScript compiler. It is unfortunate that typescript does not report this error directly - instead, it just settles for an implicit any, which is how I discovered this bug in the first place.

Thus suggested testing:

1. In an app that is using Stencil and TypeScript, install typescript-eslint and enable the @typescript-eslint/no-unsafe-return rule
2. Create a small test file like this:

import { type VNode, h } from "@stencil/core/internal";

export function a(): VNode {
  return <br />;
}

Before this PR there would be an error on line return <br />;. After this PR, there should not be an error there

[github-actions]

--strictNullChecks error report

Typechecking with --strictNullChecks resulted in 1207 errors on this branch.

That's the same number of errors on main, so at least we're not creating new ones!

reports and statistics

Our most error-prone files

Path	Error Count
src/dev-server/index.ts	37
src/mock-doc/serialize-node.ts	36
src/dev-server/server-process.ts	32
src/compiler/prerender/prerender-main.ts	22
src/testing/puppeteer/puppeteer-element.ts	22
src/runtime/client-hydrate.ts	20
src/screenshot/connector-base.ts	19
src/runtime/vdom/vdom-render.ts	17
src/compiler/config/test/validate-paths.spec.ts	16
src/dev-server/request-handler.ts	15
src/compiler/prerender/prerender-optimize.ts	14
src/compiler/sys/stencil-sys.ts	14
src/compiler/transpile/transpile-module.ts	14
src/sys/node/node-sys.ts	14
src/compiler/prerender/prerender-queue.ts	13
src/compiler/sys/in-memory-fs.ts	13
src/runtime/connected-callback.ts	13
src/runtime/set-value.ts	13
src/compiler/output-targets/output-www.ts	12
src/compiler/transformers/test/parse-vdom.spec.ts	12

Our most common errors

Typescript Error Code	Count
TS2345	366
TS2322	362
TS18048	224
TS18047	99
TS2722	37
TS2532	26
TS2531	23
TS2454	14
TS2790	11
TS2352	10
TS2769	8
TS2538	8
TS2344	6
TS2416	6
TS2493	3
TS18046	2
TS2684	1
TS2430	1

Unused exports report

There are 14 unused exports on this PR. That's the same number of errors on main, so at least we're not creating new ones!

Unused exports

File	Line	Identifier
src/runtime/bootstrap-lazy.ts	21	setNonce
src/screenshot/screenshot-fs.ts	18	readScreenshotData
src/testing/testing-utils.ts	198	withSilentWarn
src/utils/index.ts	145	CUSTOM
src/utils/index.ts	269	normalize
src/utils/index.ts	7	escapeRegExpSpecialCharacters
src/compiler/app-core/app-data.ts	25	BUILD
src/compiler/app-core/app-data.ts	115	Env
src/compiler/app-core/app-data.ts	117	NAMESPACE
src/compiler/fs-watch/fs-watch-rebuild.ts	123	updateCacheFromRebuild
src/compiler/types/validate-primary-package-output-target.ts	61	satisfies
src/compiler/types/validate-primary-package-output-target.ts	61	Record
src/testing/puppeteer/puppeteer-declarations.ts	485	WaitForEventOptions
src/compiler/sys/fetch/write-fetch-success.ts	7	writeFetchSuccessSync

[rwaskiewicz]

Hey @maxpatiiuk 👋

I created a dev build based on this branch to test it out (you can grab it yourself using npm i @stencil/core@4.12.0-dev.1706795674.f7ef54c).

Using this dev build, I tested the PR by using it to build the Ionic Framework. There are a few cases where I think this would improve type checking, I noticed a few cases where setting type Element = VNode caused a few breaking changes with the typings used in the Framework today. I'm concerned this might be confusing to developers here if they were to upgrade Stencil and the type checker began to complain.

With that in mind and the current state of this PR, I'd like to revisit this for Stencil v5. I think this is the best case scenario for improving the typings of Stencil, while trying to minimize breaking changes in minor releases.

Now that I understand the issue here/how to reproduce it, I'm going to combine the two issues linked here. In the interim, I suggest adding an any return type to your render functions, as that appears to appease the ESLint rule no-unsafe-return and aligns with the currently typed return value of render

Thanks for your patience and let me know if you have any questions!

[rwaskiewicz]

While I understand the motivation for this change, I don't think we can make this change in Stencil v4. This changes the output of typeof Host, which would constitute a breaking change.

In Stencil v4, the following code type checks without error:

import { Host } from '@stencil/core';

const Hello: typeof Host = (_props: any, children: any, utils: any) =>
  utils.map(children, child => ({
    ...child,
    vattrs: {
      ...child.vattrs,
      class: `${child.vattrs.class} add-class`,
    },
  }));

Whereas with this commit/change, it fails with:

[ ERROR ]  TypeScript: src/components/my-component/my-component.tsx:4:7
           Type '(_props: any, children: any, utils: any) => any' is not assignable to type '(props: HostAttributes) =>
           VNode'.Target signature provides too few arguments. Expected 3 or more, but got 1.

      L4:  const Hello: typeof Host = (_props: any, children: any, utils: any) =>
      L5:    utils.map(children, child => ({

[rwaskiewicz]

Similar to my comment above - while I understand the motivation for this change, it would also be a breaking change.

In Stencil v4, the following code type checks without error:

import { Fragment } from '@stencil/core';

const Hello: typeof Fragment = (_props: any, children: any, utils: any) =>
  utils.map(children, child => ({
    ...child,
    vattrs: {
      ...child.vattrs,
      class: `${child.vattrs.class} add-class`,
    },
  }));

Whereas with this commit/change, it fails with:

[ ERROR ]  TypeScript: src/components/my-component/my-component.tsx:4:7
           Type '(_props: any, children: any, utils: any) => any' is not assignable to type '(props: {}) =>
           VNode'.Target signature provides too few arguments. Expected 3 or more, but got 1.

      L4:  const Hello: typeof Fragment = (_props: any, children: any, utils: any) =>
      L5:    utils.map(children, child => ({