No type error when setting an unknown property of a JSX element

Bug Report

I've augmented solid-js's JSX.IntrinsicElements with new intrinsic elements made within my solid-js-consuming application.

When I write an unknown prop manually (not with spread as detailed in https://github.com/microsoft/TypeScript/issues/18801), I do not get a type error.

https://user-images.githubusercontent.com/297678/104986944-4a9c7c00-59c9-11eb-9a24-24edb1dd8617.mp4

🔎 Search Terms

typescript no error on unknown prop

🕗 Version & Regression Information

Not sure when this happened, but I've been trying unsuccessfully to import {JSX} into particular files to as not to clash with React's global JSX definitions, but because import {JSX} does not work (https://github.com/microsoft/TypeScript/issues/41813), I've since started trying to use the new @jsxImportSource feature as comments inside my files.

So far, I have gotten types to appear using per-file @jsxImportSource comments, and there are no other global JSX types in those files (I have segregated React JSX code from Solid.js JSX code using Project References and placing the two forms of files in separate projects with their own tsconfig to ensure only certain types are available to each group of files).

So, I'm not sure, but it could be that I'm one of the few people testing unknown waters in TypeScript, and hitting this issue.

I have not tried with an older version of TypeScript, because @jsxImportSource doesn't work there, and import {JSX} has never worked for JSX markup (#41813).

⏯ Playground Link

I tried to recreate the issue in playground, but due to https://github.com/microsoft/TypeScript-Website/issues/1427, @jsxImportSource comments to not work in the playground, so I can't reproduce a small version of my environment.

The following is my attempt to try @jsxImportSource just to get started, but no luck (same example from https://github.com/microsoft/TypeScript-Website/issues/1427):

playground

I'll see if I can make a reproduction in a repo...

💻 Code

As you see in the video, I can hover on an unknown prop, and TypeScript will infer the type of the prop as whatever value I have set it to.

For example, in the next video I changed the value to a number, and now the type shows up as a number instead of a function:

https://user-images.githubusercontent.com/297678/104987468-a9aec080-59ca-11eb-83ed-11f802b4d8ba.mp4

I have double checked that the type supplied to JSX.IntrinsicElements does not contain an index signature. There are only specific properties defined in the type of the video's timeline-scrubber.

🙁 Actual behavior

It infers unknown props.

🙂 Expected behavior

It should give a type error.

Empieza reduciendo el escenario reportado de JSX.IntrinsicElements y @jsxImportSource por archivo, usando como referencia el intento enlazado en Playground y teniendo en cuenta su limitación indicada. Traza cómo se comprueban las props JSX desconocidas escritas manualmente, manteniendo las props spread fuera del alcance. Se considera completado cuando una prop desconocida escrita manualmente produce un error de tipo sin romper la separación reportada entre JSX de Solid.js y de React.