microsoft / microsoft/TypeScript

Opaque types for WebGL

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Bug Domain: lib.d.ts Help Wanted
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Description

WebGL types are included in the default lib.d.ts. However, most types are defined as empty interfaces, which means that the compiler doesn't catch many WebGL errors.

Consider the following code:

function foo(gl: WebGLRenderingContext, fbo: WebGLFramebuffer) {
  gl.bindFramebuffer(gl.FRAMEBUFFER, fbo); // Correct call
  gl.bindFramebuffer(gl.FRAMEBUFFER, "abc"); // This should be a compile error!

  fbo = gl.createFramebuffer(); // Correct call
  fbo = new WebGLFramebuffer; // This should be a compile error!
}
  • The second parameter of gl.bindFramebuffer should be a WebGLFramebuffer object, but passing a string does not emit a compile error or warning.
  • The type WebGLFramebuffer can only be constructed via WebGLRenderingContext.createFramebuffer, calling new throws an error at runtime

Ideally, Typescript would know that WebGLFramebuffer, even though it has no public properties, cannot be constructed or converted to any other type.
I assume that this is not easy to specify with structural typing, but having such opaque types could be useful for other libraries as well (e.g., for returning handles).

If that is not possible, can we find a workaround that at least helps catching the above mentioned bugs?

For reference, here's how the above types are currently defined in lib.d.ts:

interface WebGLFramebuffer extends WebGLObject {
}
declare var WebGLFramebuffer: {
    prototype: WebGLFramebuffer;
    new(): WebGLFramebuffer;
}
interface WebGLRenderingContext {
    bindFramebuffer(target: number, framebuffer: WebGLFramebuffer): void;
    // + many other methods
}

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the WebGLFramebuffer and WebGLRenderingContext definitions shown in lib.d.ts, then trace how the compiler handles their structural types and constructor declarations. The issue is done only when TypeScript has an agreed mechanism or workaround that rejects the invalid bindFramebuffer argument and direct construction, with the behavior covered by appropriate compiler tests.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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