exportsPresence does not work for unused imports

[menelaos]

Bug report

What is the current behavior?

Setting exportsPresence to 'error' does not emit an error if the import is unused.

If the current behavior is a bug, please provide the steps to reproduce.

1. git clone https://github.com/rwieruch/minimal-webpack-setup
2. cd minimal-webpack-setup
3. npx npm-check-updates -u
4. npm install
5. Create src/foo.js with the following content:

   export const foo = 42;

6. Modify webpack.config.js to include

   module: { parser: { javascript: { exportsPresence: 'error' } } },

7. Modify src/index.js to look like:

   import { bar, foo } from './foo';
   
   console.log(foo);
   
   // Uncommenting the following line will result in an error
   // console.log(bar);

8. npx webpack

What is the expected behavior?

Webpack should emit an error that bar is an invalid import regardless of whether console.log(bar) is commented out or not.

Other relevant information:
webpack version: 5.91.0
Node.js version: 21.7.1

This seems to be a regression since the same issue was reported a few years ago and allegedly resolved (#4897).

[alexander-akait]

hm, intresting, no sure we can't fix it, because we don't handle at all unused imports for perf reasons, maybe linter is the best solution here, but I look at this deeply

[alexander-akait]

@vankop What do you think? Honestly, I'm not sure that we should process this, personally I think it's more work for a linter, because bar import is not unsed and we just drop it, so we don't generate broken code

[vankop]

probably original issue was closed as a stale one..

So basically idea of the warning/error here is to notify user about highly likely issues at runtime ( if exports are reachable code ), with unused imports it is not a problem. If you didn't disable optimisations in config, webpack will remove unused exports for you.

If you want to improve your source code, in this case better to use linters (e.g. eslint )