Enable parserOptions.allowAutomaticSingleRunInference

Coming over from https://twitter.com/andhaveaniceday/status/1738986013320794313: typescript-eslint has a relatively undocumented allowAutomaticSingleRunInference feature that in many cases speeds up single-run linting. That includes CI.

Because eslint/rfcs#102 wasn't accepted (😞) and one last bug with it has yet to be explained (typescript-eslint/typescript-eslint#3851), we've been cautious to enable it by default in typescript-eslint. But as @jakebailey noted, [DT doesn't] have project references and it's all single run outside of the editor.

I misspoke; we do run in the editor, I actually just meant that the big single run is the "slow" run. Does this negatively impact the editor? Should this be set in the runner instead?

Does this negatively impact the editor?

I don't believe it does, no. @bradzacher can probably keep me honest - but to my knowledge the only known issue is the mysterious one from the case that uses project references.

Note that if you've got custom scripts to run eslint we won't be able to infer it as a CLI run and so the option will do nothing. You'll need to set the env var to force it on for that case.

What's the env var? I must have missed it trying to look through the docs.

TSESTREE_SINGLE_RUN=true should do it for you

Thanks! I think we should probably just set that right at the start of dtslint's main entrypoint, and skip the setting (given it won't work). When I (or someone else) gets a chance, I'll be curious to benchmark it.

I also want to try the ProjectService, though I suspect that there will be some OOMing because the functionality to ask it to drop files is probably not there yet.

So, it turns out that we already do this:

DefinitelyTyped-tools/packages/dtslint/src/lint.ts

Line 22 in d64f518

process.env.TSESTREE_SINGLE_RUN = "true";

Removing that, then benchmarking reenabling it, shows that it unfortunately does not help:

Benchmark 1: pnpm test gensync
  Time (mean ± σ):      5.412 s ±  0.022 s    [User: 8.465 s, System: 0.588 s]
  Range (min … max):    5.372 s …  5.435 s    10 runs
 
Benchmark 2: TSESTREE_SINGLE_RUN=true pnpm test gensync
  Time (mean ± σ):      5.444 s ±  0.050 s    [User: 8.517 s, System: 0.599 s]
  Range (min … max):    5.374 s …  5.521 s    10 runs
 
Summary
  'pnpm test gensync' ran
    1.01 ± 0.01 times faster than 'TSESTREE_SINGLE_RUN=true pnpm test gensync'

So, I guess this issue can be closed as we're already enabling it... but is it suspicious that it doesn't actually help?

Heh, maybe the issue should be tracking why it doesn't actually help?

But we're also planning on enabling it by default in v7 (typescript-eslint/typescript-eslint#8121). And this issue isn't very high on my priority queue to investigate. So I'm probably not going to be taking action soon tbh.