`--fix` mangles TypeScript files outside the program

[patrik-csak]

Given:

• XO v3.0.1

• Project structure:

  .
  ├── source/
  │   └── index.ts
  └── test/
      └── index.ts
  

• TSConfig:

  {
  	"include": ["source/**/*"],
  	"compilerOptions": {
  		"outDir": "distribution",
  		"rootDir": "source",
  		"types": ["node"]
  	}
  }

• The same file at both source/index.ts and test/index.ts:

  import assert from 'node:assert/strict';
  import {test} from 'node:test';
  
  function fn(integer: number) {
  	if (!Number.isSafeInteger(integer)) {
  		throw new RangeError('Not an integer');
  	}
  }
  
  void test('throws RangeError for invalid numbers', () => {
  	assert.throws(() => fn(Number.NaN), RangeError);
  	assert.throws(() => fn(1.5), RangeError);
  });

xo reports the same issues in both files:

npx xo source/index.ts test/index.ts

source/index.ts:11:22
✖  11:22  Returning a void expression from an arrow function shorthand is forbidden. Please add braces to the arrow function.  @typescript-eslint/no-confusing-void-expression
✖  11:25  Prefer NaN over Number.NaN.                                                                                          unicorn/prefer-global-number-constants
✖  12:22  Returning a void expression from an arrow function shorthand is forbidden. Please add braces to the arrow function.  @typescript-eslint/no-confusing-void-expression

test/index.ts:11:22
✖  11:22  Returning a void expression from an arrow function shorthand is forbidden. Please add braces to the arrow function.  @typescript-eslint/no-confusing-void-expression
✖  11:25  Prefer NaN over Number.NaN.                                                                                          unicorn/prefer-global-number-constants
✖  12:22  Returning a void expression from an arrow function shorthand is forbidden. Please add braces to the arrow function.  @typescript-eslint/no-confusing-void-expression

6 errors

xo --fix fixes source/index.ts as expected, but mangles test/index.ts

npx xo --fix source/index.ts test/index.ts

source/index.ts:

 void test('throws RangeError for invalid numbers', () => {
- assert.throws(() => fn(Number.NaN), RangeError);
- assert.throws(() => fn(1.5), RangeError);
+	assert.throws(() => { fn(NaN); }, RangeError);
+	assert.throws(() => { fn(1.5); }, RangeError);
 });

test/index.ts:

 void test('throws RangeError for invalid numbers', () => {
- assert.throws(() => fn(Number.NaN), RangeError);
- assert.throws(() => fn(1.5), RangeError);
+	assert.throws(() => { { { { { { { { ; }{ ; }{ ; }fn; }(N; }um; }be; }r.; }N{ a; }N{ ; }); },{ ; } Rang{ ; }eErro{ ; }r);
+	{ ; }asser{ ; }t.thr{ ; }ows(({ ; }) => { ; }fn(1.5); }, RangeError);
 });

[patrik-csak]

Thanks, @sindresorhus!