error: Parsing error: "parserOptions.project" has been set for @typescript-eslint/parser.

[ljwagerfield]

Repro

Run eslint . --ext .js,.jsx,.ts,.tsx on the following codebase:

/.eslintrc.yaml

root: true
parser: "@typescript-eslint/parser"
parserOptions:
  project: "./tsconfig.json"
plugins:
  - "@typescript-eslint"
env:
  node: true

/tsconfig.json

{
  "compilerOptions": {
    "lib": ["es2019"],
    "module": "commonjs",
    "target": "es2019",
    "strict": true,
    "esModuleInterop": true,
    "allowJs": true,
    "checkJs": true,
    "baseUrl": "./"
  },
  "include": ["./**/*"],
  "exclude": ["./node_modules/**/*"]
}

/package.json

{
  "devDependencies": {
    "@typescript-eslint/eslint-plugin": "4.8.2",
    "@typescript-eslint/parser": "4.8.2",
    "eslint": "7.14.0",
    "typescript": "4.1.2"
  }
}

/src/Foo.ts

export default function foo(): string {
  return "";
}

/src/Foo.js

export default function foo() {
  return "";
}

Expected Result

eslint to succeed.

Actual Result

eslint fails due to Foo.js not being included within the project (even though it's covered by my "include" settings):

/Users/lawrence/Repositories/playground/eslint-js-example/src/Foo.js
  0:0  error  Parsing error: "parserOptions.project" has been set for @typescript-eslint/parser.
The file does not match your project config: src/Foo.js.
The file must be included in at least one of the projects provided

✖ 1 problem (1 error, 0 warnings)

Versions

package	version
@typescript-eslint/parser	4.8.2
TypeScript	4.1.2
ESLint	7.14.0
node	12.19.0

[bradzacher]

This is a known problem with typescript and files named the same.
Nothing we can do about it unfortunately!

Please checkout the readme - this is explicitly called out!

https://github.com/typescript-eslint/typescript-eslint/tree/master/packages/parser#parseroptionsproject

TypeScript will ignore files with duplicate filenames in the same folder (for example, src/file.ts and src/file.js). TypeScript purposely ignore all but one of the files, only keeping the one file with the highest priority extension (the extension priority order (from highest to lowest) is .ts, .tsx, .d.ts, .js, .jsx). For more info see #955.

Also this is a duplicate of #955

[ljwagerfield]

Thank you for the fast response 😄