Test fails using yarn@berry and pnp-webpack-plugin

[irudoy]

🐛 Bug Report

Testing webpack build with babel-jest fails using yarn@berry and pnp-webpack-plugin.

test.js

const webpack = require('webpack');

test('simple', () => {
    expect(
        webpack({
            resolve: {
                plugins: [require('pnp-webpack-plugin')],
            },
        })
    ).not.toThrow();
});

output

    The whole PnP file got strict-mode-ified, which is known to break (Emscripten libraries aren't strict mode). This usually happens when the file goes through Babel.

       5 |   Object.freeze({}).detectStrictMode = true;
       6 | } catch (error) {
    >  7 |   throw new Error(`The whole PnP file got strict-mode-ified, which is known to break (Emscripten libraries aren't strict mode). This usually happens when the file goes through Babel.`);
         |         ^
       8 | }
       9 |
      10 | var __non_webpack_module__ = module;

      at Object.<anonymous> (.pnp.js:7:9)
      at Object.<anonymous> (index.test.js:7:27)

To Reproduce

https://github.com/irudoy/yarn-berry-webpack-jest-repro

Expected behavior

The test is successfully passed.

Link to repl or repo (highly encouraged)

https://github.com/irudoy/yarn-berry-webpack-jest-repro

envinfo

  System:
    OS: macOS 10.15.4
    CPU: (8) x64 Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
  Binaries:
    Node: 14.2.0 - /usr/local/bin/node
    Yarn: 2.0.0-rc.33 - /usr/local/bin/yarn
    npm: 6.14.4 - /usr/local/bin/npm

[irudoy]

there was a workaround for webpack@4

resolve: {
  plugins: IS_TEST ? [] : [require('pnp-webpack-plugin')],
},

but webpack@5 supports yarn pnp by default, so it's not working anymore

[SimenB]

@arcanis any ideas?

[arcanis]

Can't check right now, but I suspect babel-jest is transpiling the .pnp.js file, which it shouldn't do for the reason described in the error message. I'd suggest to try disabling transforms on this file.

[SimenB]

Interesting! Our current default transformIgnorePatterns is just node_modules - should we add .pnp.js as well?

[arcanis]

That would be ideal! In fact, if you can ignore .pnp.* it would probably be the best - we'll likely change the file name to .pnp.cjs in the next major, otherwise it causes problem with projects configured for ESM.

[SimenB]

@irudoy can you confirm adding .pnp.js to transformIgnorePatterns fixes the issue?

[irudoy]

Adding .pnp.js to transformIgnorePatterns fixes the issue, but only for webpack 4. For webpack 5 it didn't work, and it still throws.

[arcanis]

Curious - afaik Webpack 5 also simply requires pnpapi, I don't know why it would still be transpiled 🤔

[irudoy]

I'm sorry for the misinformation. Definitely, it's working just fine with webpack 5! It was late at night, and I missed something.

Big thanks for finding a solution 😸

@SimenB this should be added to the default value of transformIgnorePatterns, I guess?

[SimenB]

Yeah, let's do it. Wanna send a PR?

[irudoy]

done

[github-actions]

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