Document webpack change: Add loader name to error message. Resolves #2878

[webpack-bot]

A pull request by @mc-zone was merged and maintainers requested a documentation change.

See pull request: webpack/webpack#6542

---

What kind of change does this PR introduce?
Feature.

Did you add tests for your changes?
Yes.

If relevant, link to documentation update:
N/A

Summary
Add loader name to Error message so that people can actually realize which loaders were emiting these errors clearly.

Demo:

webpack.config.js:

module.exports = {
  entry:"./index.js",
  output:{
    path:path.resolve(__dirname, "./dist"),
    filename:"[name].bundle.js",
  },
  mode:"development",
  module: {
    rules: [
      {
        test: /\.test$/,
        use: [
          "babel-loader",
          {
            loader:path.resolve(__dirname, './test-loader.js'),
          }
        ]
      },
    ]
  },
};

test-loader.js:

module.exports = function(source){
  this.emitWarning(new Error("This is a emit Warning"));
  this.emitError(new Error("This is a emit Error"));
  return source;
};

lib.test:

);a
console.log("I'm test");

Current output:

After this PR:

Resolves #2878.

Does this PR introduce a breaking change?
Nope (I think).

Other information
Note: This feature also need some changes in webpack/loader-runner to handle errors from throw and callback(error) (need add loader name to error.from). I will add it subsequently.
Updated: Now using loaderContext.loaderIndex in NormalModule.js for all to determine which loader the error is belong to .

[EugeneHlushko]

Hi @sokra i am not sure what we can update from this one, can you point out please?

[EugeneHlushko]

@ooflorent can you pls check this ?

[montogeek]

@EugeneHlushko Maybe update examples that show those errors?

[ooflorent]

Yeah, @montogeek is right. This issue has been open because the error messages used in the documentation may require an update.

[mc-zone]

Sorry for my late. Just let me try to update this tomorrow ☺