Bug: "Too many files (>8) have matched the default project" error triggers on every file after 8

[ehoogeveen-medweb]

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• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
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Issue Description

Split out from #8925 as I realized you requested an issue. As the title says, this error seems to trigger for every file after the 8th. With 9 files I get the error once, with 10 files I get the error twice, etc.

Reproduction Repository Link

https://github.com/ehoogeveen-medweb/glob-too-wide.git

Repro Steps

1. clone the repo
2. npm ci
3. npx eslint --ext ts .

Versions

package	version
typescript-eslint	7.8.0
TypeScript	5.4.5
ESLint	8.57.0
node	20.12.2

[ehoogeveen-medweb]

Workaround: Set parserOptions.EXPERIMENTAL_useProjectService.maximumDefaultProjectFileMatchCount_THIS_WILL_SLOW_DOWN_LINTING to some huge value like Infinity.

{
  parserOptions: {
    EXPERIMENTAL_useProjectService: {
      maximumDefaultProjectFileMatchCount_THIS_WILL_SLOW_DOWN_LINTING: Infinity,
    },
  },
}

(but note that Infinity isn't supported by JSON so you'll need to use a finite number like 1e10 in JSON-based configs)

[JoshuaKGoldberg]

Un-assigning from myself as I'm on vacation and then conference-traveling this month, and won't have time to investigate. If anybody would like to dive into the code to investigate then please do!

maximumDefaultProjectFileMatchCount_THIS_WILL_SLOW_DOWN_LINTING is appropriately obnoxiously named. It's a "bandaid" solution to files being unmatched by the project service. A better solution is to figure out why they're unmatched and fix that bug - which is either in the ESLint config being used or in typescript-eslint.

As mentioned, #8925 is the PR that added these new code paths. That PR touches the relevant files in packages/typescript-estree you'll likely want to look at first.

[ehoogeveen-medweb]

I've updated the reproduction to typescript-eslint version 7.9.0 and set maximumDefaultProjectFileMatchCount_THIS_WILL_SLOW_DOWN_LINTING: 0 to simplify the reproduction.

[ehoogeveen-medweb]

Looking at the code, I think the problem might be here:

typescript-eslint/packages/typescript-estree/src/useProgramFromProjectService.ts

Line 86 in 77fc366

defaultProjectMatchedFiles.add(filePathAbsolute);

It unconditionally does

  defaultProjectMatchedFiles.add(filePathAbsolute);

so every file will be considered as matching the default project. If I understand the code correctly, it should be checking against opened.configFilename:

  if (!opened.configFileName) {
    defaultProjectMatchedFiles.add(filePathAbsolute);
  }

I've tried adding that check locally and no longer get the warnings (but I haven't checked to see if files that actually don't have a project still trigger it).

[JoshuaKGoldberg]

@ehoogeveen-medweb excellent find, thanks for pointing this out! Are you up for sending a PR to fix this? 😁

[ehoogeveen-medweb]

Technically I think the old title was more accurate if my diagnosis is correct, as it's in-project files getting reported as out-of-project files 😁

I'll try to put together a pull request.

[JoshuaKGoldberg]

Haha fair point!