Cypress extreme slow initial test with Webpack 5 + Typescript

[petermanders89]

Current behavior

The first test run with open is extreme slow with Webpack 5 and a typescript setup. However when using run command it goes fast (as expected). Downgrading to Webpack 4 makes it a lot faster. The message "Your tests are loading" takes about 2 minutes. After which it proceeds to execute the test. Running this with the cypress-preprocessor-webpack-5 did not change anything. I added a complete debug log from a webpack 5 run. Tested with Chrome on Linux, however this also occurs on FireFox and other browsers. I tested on Windows as well, same issue.

Desired behavior

The first test with Webpack 5 should be equally fast as Webpack 4.

Test code to reproduce

I have provided a test repository: https://github.com/petermanders89/cypress-test-repo

Versions

You can see it in the repository, but here are the installed and used versions. Changing Webpack 5 to Webpack 4 solves it, but that's not desired behavior.

{
    "@babel/core": "^7.13.10",
    "@babel/preset-env": "^7.13.10",
    "@babel/preset-typescript": "^7.13.0",
    "@cypress/webpack-preprocessor": "^5.6.0",
    "babel-loader": "^8.2.2",
    "cypress": "^6.6.0",
    "typescript": "^4.2.3",
    "webpack": "^5.25.0"
}

logs.txt

[lukeapage]

this is exactly what I've been investigating. What happens is that inside the cypress plugin

https://github.com/cypress-io/cypress/blob/develop/npm/webpack-preprocessor/index.ts#L305

onCompile is called before the timeout finishes for the handler is called with the result:
https://github.com/cypress-io/cypress/blob/develop/npm/webpack-preprocessor/index.ts#L297

Therefore the handler resolves the 2nd promise - but the 1st promise is the one that is sent back to the proprocessor and the ipc interface.

The call to get the js times out after 2 minutes and is retried. The second time the file is in the cache and is served.

I get this most of the time in webpack 5, but it is intermittant.

[cypress-bot]

The code for this is done in cypress-io/cypress#15611, but has yet to be released.
We'll update this issue and reference the changelog when it's released.

[cypress-bot]

Released in 7.6.0.

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Cypress v7.6.0, please open a new issue.