[no-namespace] Allow namespaces in module and the global namespace augmentation

[cherryblossom000]

Repro

{
  "rules": {
    "@typescript-eslint/no-namespace": [2, {"allowDeclarations": true}]
  }
}

declare module 'fs' {
  namespace SomeNamespace {}
}

declare global {
  namespace Intl {}
}
export {}

Expected Result
No error because the namespaces are being declared in a module augmentation or in the global namespace. declare namespace can't be used because it's already in an ambient context.

Actual Result

/path/to/file.ts
  2:3  error  ES2015 module syntax is preferred over custom TypeScript modules and namespaces  @typescript-eslint/no-namespace
  6:3  error  ES2015 module syntax is preferred over custom TypeScript modules and namespaces  @typescript-eslint/no-namespace

✖ 2 problems (2 errors, 0 warnings)

Additional Info

Versions

package	version
@typescript-eslint/eslint-plugin	3.3.0
@typescript-eslint/parser	3.3.0
TypeScript	3.9.5
ESLint	7.3.0
node	12.18.0
npm	6.14.5

[bradzacher]

happy to accept a pr!

[rrrix]

Would this also be applicable to how Jest recommends extending expect with custom matchers?

https://jestjs.io/docs/en/expect#expectextendmatchers

declare global {
  namespace jest {
    interface Matchers<R> {
      toBeWithinRange(a: number, b: number): R;
    }
  }
}

expect.extend({
  toBeWithinRange(received, floor, ceiling) {
    const pass = received >= floor && received <= ceiling;
    if (pass) {
      return {
        message: () =>
          `expected ${received} not to be within range ${floor} - ${ceiling}`,
        pass: true,
      };
    } else {
      return {
        message: () =>
          `expected ${received} to be within range ${floor} - ${ceiling}`,
        pass: false,
      };
    }
  },
});

test('numeric ranges', () => {
  expect(100).toBeWithinRange(90, 110);
  expect(101).not.toBeWithinRange(0, 100);
  expect({apples: 6, bananas: 3}).toEqual({
    apples: expect.toBeWithinRange(1, 10),
    bananas: expect.not.toBeWithinRange(11, 20),
  });
});

Today this gives me an error with ESLint: ES2015 module syntax is preferred over custom TypeScript modules and namespaces.(@typescript-eslint/no-namespace).

I'm using all the defaults:

  plugins: ['@typescript-eslint'],
  extends: [
    'plugin:@typescript-eslint/recommended',
  ],

Is there a right / better/ correct way to do this with Jest?

[cherryblossom000]

@rrrix That was actually one of the reasons why I opened this issue. I don't think there is another way of adding types for custom Jest matchers, so just use // eslint-disable-next-line @typescript-eslint/no-namespace for now until #2238 is merged.