discuss for remove unused argument in runtime function template in webpack5

I’m not sure if this is a bug or expected feature(not compatibility for the wrong module library)，so I marked it as discuss.

good case

when we not use module spec keyword like module,require ,import,export etc in js file

// a.js
console.log(1)

in webpack4 ,we will get output like

function(module, exports){
  console.log(1)
}

but webpack5 ( maybe this commit ) ,we will get output like

function(/* argument is omit for unused */){
  console.log(1)
}

I think this is a useful optimization in most cases。

bad case

However. suppose you have a library whick name “A”

// my simple lib A
eval("if(typeof module === 'object') module.exports='A'")

in webpack4 we will get string "A" with import A from "A"

function(module, exports){
  eval("if(typeof module === 'object') module.exports='A'")
}

but in webpack5 we get an empty object {}. because arcon ast can not detect the correlation of the module variable.so that the first module argument will be remove due to unused

function(/* argument is omit for unused */){
  eval("if(typeof module === 'object') module.exports='A'")
}

real case

we use a lib which name watermark-dom(it has a star close to 1k github npm) in webpack5

Below is the minimal reproduce link https://github.com/VisonM/webpack-reproduce-demo

Summarize

I have to say the npm package of watermark-dom is terrible, but do we still need to be compatible with such libs？if we should keep unused argument when code exist some keyword like eval,new Function etc

[VisonM]

@alexander-akait @vankop Thanks for your patience！🌈 just closed this issue.

I think noParse is enough for such weird libraries.

I also found docs about runtime optimization in release blog, but I think it’s a little obscure for developers, I may send a docs pr to optimized, make it more understandable, but it’s a bit difficult for me, I haven’t done anything like that, but I’ll try my best.

[alexander-akait]

but,I don’t see any instructions about this in the relevant weback documentation or migration guide, am I missing something? I think adding documentation may be helpful to those who care it, and I’m willing to contribute pr if needed

These changes happen because webpack v5 is more stricky

Workaround:

module.exports = {
  module: {
    noParse: /watermark-dom/,
  },
  target: ["web", "es5"], // remove arrow function in output
};

But I think it’s really weird and I don’t think this code should be used in libraries

And yes - welcome to update docs