Webpack 4 support

[filipesilva]

Briefly describe the issue you are experiencing (or the feature you want to see
added to the plugin). Tell us what you were trying to do and what happened
instead. Remember, this is not a place to ask questions. For that, go to
http://gitter.im/postcss/postcss

Details

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Trying to use postcss-loader with webpack@4.0.0-alpha.0 (webpack/webpack#6064).

Error (Logs|Stacks)

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The main error seems to be Module build failed: TypeError: loader._compilation.applyPluginsWaterfall is not a function.

ERROR in D:/work/angular/aio/node_modules/css-loader?{"sourceMap":false,"importLoaders":1}!D:/work/angular/aio/node_modules/postcss-loader?{"ident":"postcss","sourceMap":false}!D:/work/angular/aio/node_modules/sass-loader/lib/loader.js?{"sourceMap":false,"precision":8,"includePaths":[]}!D:/work/angular/aio/src/styles.scss
Module build failed: TypeError: loader._compilation.applyPluginsWaterfall is not a function
    at D:\work\angular\aio\node_modules\postcss-loader\index.js:122:43
    at <anonymous>
 @ D:/work/angular/aio/src/styles.scss 4:14-189
 @ multi D:/work/angular/aio/src/styles.scss

Reproduction [Code]

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I think this happens whenever postcss-loader is used with Webpack 4, but if you think that's not the case and need to zone in on the issue let me know and I will make a repro.

Environment

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Please provide information about your environment.

OS	node	npm	PostCSS
Windows 10	8.9.1	5.6.0	2.0.8

[michael-ciniawsky]

hmm.. I wonder where this is actually coming from in v2.0.0 since I removed the 'Custom Plugin Compilation Hook' in v1.0.0...v2.0.0. Could you point my to the where in angular-cli the loader is getting used atm ?

[filipesilva]

We use it here: https://github.com/angular/angular-cli/blob/master/packages/@angular/cli/models/webpack-configs/styles.ts#L175-L182

But now that you mention the versions, I went and checked and it seems that in that project the postcss-loader version was actually 1.3.x. I updated to 2.0.8 and didn't have that problem anymore. So, user error :/

[TimeBandit]

Saw same issue, upgrading to "postcss-loader": "^2.1.5" and the problem went away

[OliverJAsh]

What was the exact fix for this issue, and in which release did it first appear?

Upgrading to the latest version isn't a great solution, as many times that only replaces old bugs for new bugs (as I have just found). If we can work in terms of specific fixes, then we can deal with bugs on a case-by-case basis.

[OliverJAsh]

It appears the fix for this issue first appeared in v2.0.0, although the changelog doesn't mention it: https://github.com/postcss/postcss-loader/blob/928d5c41d5e2bdec130b3c0899760889466ae7bd/CHANGELOG.md#200-2017-05-08

From this PR: #191