Xunnamius commented 2 years ago

Bug Report

🔎 Search Terms

tsserver typescript langauge server loading intellisense status indefinite error forever asserts assertion function vscode conditional type

🕗 Version & Regression Information

This changed between versions 4.7.4 and 4.8.0-beta and happens in all versions up to 4.9.0-dev.20221015

⏯ Playground Link

Unfortunately, painstakingly copy-pasting all the types from the various packages into the playground doesn't allow me to reproduce the issue. So instead, I've created a minimal example repository that demonstrates the issue: https://github.com/Xunnamius/mre-typescript-issue-51188

💻 Code

import { visit, SKIP, type Visitor } from 'unist-util-visit';

import type { Content as MdastContent } from 'mdast';

function assertNonNullable<T>(
  value: T,
  err: string
): asserts value is NonNullable<T> {
  if (value === null) {
    throw new Error(err);
  }
}

export function visitAndReveal<Tree extends MdastContent>(
  tree: Tree,
  visitor?: Visitor,
  reverse?: boolean
) {
  visit(
    tree,
    'hidden',
    (node, index, parent) => {
      // UNCOMMENTING THIS WILL KILL INTELLISENSE
      // assertNonNullable(
      //   index,
      //   'error while revealing hidden node: node index is missing'
      // );

      // UNCOMMENTING THIS WILL KILL INTELLISENSE
      // assertNonNullable(
      //  parent,
      //  'error while revealing hidden node: node parent is missing'
      //);

      return visitor?.(node, index, parent) ?? [SKIP, index];
    },
    reverse
  );
}

🙁 Actual behavior

Tsserver and intellisense in vscode (latest version) hang when using a TypeScript version >=4.8.0-beta. See video example below.

🙂 Expected behavior

Tsserver/intellisense does not hang in latest versions of vscode and TypeScript.

https://user-images.githubusercontent.com/656017/195998496-e83d5c99-dc27-4867-8bcc-aa3d6a54ff55.mp4

jakebailey commented 2 years ago

This seems to bisect to #49119.

ahejlsberg commented 2 years ago

Stumbled across this one and took a quick look. The core issue is that the types in the repo are very expensive to compute, as is evident by the painful slowness of intellisense in the example. For example, checking the visitAndReveal function in the example causes ~5.8M type instantiations in 4.7 when compiled with tsc. This shrinks to ~1.2M type instantiations in 4.8 and later. Those numbers are big warning flags that the types are too complex.

That said, we obviously shouldn't hang the language service and I'm not sure why that happens. The example compiles with tsc with or without the commented out section, and I would expect the same from the language service.

jakebailey commented 2 years ago

Very odd that we hang in 4.8+ when those versions have the fewer instantiations; I would have assumed the opposite.

Xunnamius commented 2 years ago

For example, checking the visitAndReveal function in the example causes ~5.8M type instantiations in 4.7 when compiled with tsc. This shrinks to ~1.2M type instantiations in 4.8 and later. Those numbers are big warning flags that the types are too complex.

Thanks for taking a look! I had a suspicion complexity was a problem after some other small issues with the types coming from the unist-util-visit package. For example, sometimes TS would give me "Type instantiation is excessively deep and possibly infinite" seemingly at random, then I'd restart the language server, and it would return the expected type.

cc unified team: @wooorm

ahejlsberg commented 2 years ago

For example, sometimes TS would give me "Type instantiation is excessively deep and possibly infinite" seemingly at random

That error is caused by our type instantiation governor when a single source element gives rise to >5M type instantiations. Any code that triggers this is definitely highly suspect. It looks like you were barely managing to squeeze under the limit in 4.7, so I would strongly recommend simplifying the types. In particular, the InclusiveDescendant<...> type appears expensive. I think it is trying to reduce the set of possible descendant types. I don't know how important that added precision is, but it clearly comes at a very high cost.

wooorm commented 2 years ago

A TS wizard can probably improve InclusiveDescendant. It’s quite useful though, I’d rather not yank it out if possible.