index.js

// Dependencies
var loaderUtils = require('loader-utils');
var assign = require('object-assign');

// Modules
var linter = require('./lib/linter');

// Check if plugin is ignored
function ignorePlugins(plugins, currentPlugin) {
  return plugins.reduce(function (acc, plugin) {
    if (currentPlugin && currentPlugin.indexOf(plugin) > -1) {
      return true;
    }

    return acc;
  }, false);
}

function apply(options, compiler) {
  // access to compiler and options
  compiler.plugin('compilation', function(compilation, params) {
    // Avoid redundant lint when it comes to running with other plugins
    if (options.ignorePlugins &&
      ignorePlugins(options.ignorePlugins, compilation.name)
    ) {
      return;
    }

    // Linter returns a simple report of FilePath + Warning or Errors
    var contexts = options.context || [compiler.context];
    var report = [];
    contexts.forEach(function(context) {
      report = report.concat(linter(context + '/' + options.glob, options));
    });

    // Hook into the compilation as early as possible, at the seal step
    compilation.plugin('seal', function() {
      // We need to keep the reference to the compilation's scope
      var _this = this;

      // Errors/Warnings are pushed to the compilation's error handling
      // so we can drop out of the processing tree on warn/error
      report.forEach(function(x) {
        if(x.error) {
          _this.errors.push(x.file);
        } else {
          _this.warnings.push(x.file);
        }
      });
    });
  });
}

// makes it easier to pass and check options to the plugin thank you webpack doc
// [https://webpack.github.io/docs/plugins.html#the-compiler-instance]
module.exports = function(options) {
  options = options || {};
  // Default Glob is any directory level of scss and/or sass file,
  // under webpack's context and specificity changed via globbing patterns
  options.glob = options.glob || '**/*.s?(c|a)ss';

  var arrayOptions = [
    'ignoreFiles',
    'ignorePlugins',
    'context'
  ];

  arrayOptions.forEach(function(option) {
    if(options[option] && typeof options[option] === 'string') {
      options[option] = [options[option]];
    }
  });

  if (options instanceof Array) {
    options = {
      include: options,
    };
  }

  if (!Array.isArray(options.include)) {
    options.include = [options.include];
  }

  return {
    apply: apply.bind(this, options)
  };
};