PostCSS does not honor options passed to Autoprefixer

• Laravel Mix Version: 1.5.1
• Node Version: 8.5.0
• NPM Version: 5.4.2
• OS: OS X El Capitan v10.11.5

Description:

Attempting to pass custom options to Autoprefixer through the postCss array appears to do nothing.

Custom options may be necessary when dealing with cross-device / cross-browser QA on common frontend frameworks like Bootstrap.

Steps To Reproduce:

package.json

{
  "private": true,
  "scripts": {
    "dev": "./node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js"
  },
  "devDependencies": {
    "bootstrap": "^4.0.0-alpha.6",
    "laravel-mix": "^1.0"
  }
}

webpack.mix.js

let mix = require('laravel-mix');

mix.sass('assets/scss/main.scss', 'public/css');
mix.sass('assets/scss/main2.scss', 'public/css').options({
    postCss: [
        require('autoprefixer')({
            browsers: [
                'last 2 versions',
                'iOS >= 8',
                'Safari >= 8',
            ],
            cascade: false,
            flexbox: "no-2009"
        }),
    ]
});

assets/main.scss

@import '~bootstrap/scss/bootstrap';

assets/main2.scss

@import '~bootstrap/scss/bootstrap';

Then run npm run dev.

Note that the output of public/css/main.css and public/css/main2.css are identical.

Hardcoding in some options on line 160 of /src/builder/webpack-rules.js will yield the desired results. Differences can be found by turning off one of the sass tasks and running the build with hardcoded options in place:

plugins.push(require('autoprefixer')({
    browsers: [
        'last 2 versions',
        'iOS >= 8',
        'Safari >= 8',
    ],
    cascade: false,
    flexbox: "no-2009"
}));

Is there something I could be missing? Is there a place I can pass in Autoprefixer options without altering source code?

[exfriend]

Thanks @AndreasElia and great job @JeffreyWay !

[andreaselia]

@maiorano84 did you solve this issue?