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enable webpack sideEffects for css and scss files #3805

Merged
merged 1 commit into from
Jul 27, 2020
Merged

enable webpack sideEffects for css and scss files #3805

merged 1 commit into from
Jul 27, 2020

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chandlerprall
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@chandlerprall chandlerprall commented Jul 27, 2020 •
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Summary

Closes #3397

Marks EUI's *.css and *.scss files as having sideEffects when they are imported by webpack. Setup I tested with:

package.json 
{
  "name": "test",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "dependencies": {
    "@babel/core": "^7.10.5",
    "@babel/preset-env": "^7.10.4",
    "@babel/preset-react": "^7.10.4",
    "@elastic/datemath": "^5.0.3",
    "@elastic/eui": "^27.2.0",
    "babel-loader": "^8.1.0",
    "css-loader": "^4.0.0",
    "lodash": "^4.17.19",
    "moment": "^2.27.0",
    "react": "^16.13.1",
    "react-dom": "^16.13.1",
    "style-loader": "^1.2.1",
    "webpack": "^4.44.0",
    "webpack-cli": "^3.3.12",
    "webpack-dev-server": "^3.11.0"
  }
}
webpack.config.js 
const path = require('path');

module.exports = {
	mode: 'production',

	entry: path.resolve(__dirname, './src/index.js'),

	output: {
		path: path.resolve(__dirname, 'dist'),
		filename: 'bundle.js',
	},

	module: {
		rules: [
			{
				test: /\.(js|tsx?)$/,
				loader: 'babel-loader',
				options: {
					babelrc: false,
					presets: [
						'@babel/react',
						'@babel/env'
					],
				},
				exclude: /node_modules/,
			},
			{
				test: /\.css$/,
				loaders: [
					'style-loader',
					'css-loader',
				],
			},
		],
	},
};
src/index.js 
import React from 'react';
import ReactDOM from 'react-dom';
import { EuiButton } from '@elastic/eui';
import '@elastic/eui/dist/eui_theme_dark.css';

const App = () => (
	<>
		<EuiButton onClick={() => {}}>Click Me!</EuiButton>
	</>
);

ReactDOM.render(
	<App/>,
	document.getElementById('app')
);
dist/index.html 
<!DOCTYPE html>
<html>
	<body>
		<div id="app"></div>
		<script type="text/javascript" src="./bundle.js"></script>
	</body>
</html>

First confirmed that the css imports were tree-shaken away, and the page left unstyled. Then I manually applied the change in this PR to node_modules/@elastic/eui/package.json and rebuilt, confirming the expected styles were then present.

This change somewhat makes the assumption that the usual css-loader/style-loader configuration is used, which does follow our consuming.md documentation. If the files are instead processed with a loader like css modules, turning them into import Styles from '...', then there is technically no side effect, as the contents are handled elsewhere - but this change would have no effect as they are already imported. However, this change could in theory bloat applications which are configured to use css modules but have an import '@elastic/eui/dist/some_theme.css'; as that would have previously been [correctly] tree shaken out. My concern for that case is barely measurable 😁

/cc @clintandrewhall

Checklist

- [ ] Check against all themes for compatibility in both light and dark modes
- [ ] Checked in mobile
- [ ] Checked in IE11 and Firefox
- [ ] Props have proper autodocs
- [ ] Added documentation
- [ ] Checked Code Sandbox works for the any docs examples
- [ ] Added or updated jest tests

  • Checked for breaking changes and labeled appropriately
    - [ ] Checked for accessibility including keyboard-only and screenreader modes
  • A changelog entry exists and is marked appropriately

@chandlerprall chandlerprall requested a review from thompsongl July 27, 2020 18:33
@kibanamachine
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Preview documentation changes for this PR: https://eui.elastic.co/pr_3805/

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@kibanamachine
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Preview documentation changes for this PR: https://eui.elastic.co/pr_3805/

thompsongl
thompsongl approved these changes Jul 27, 2020
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@thompsongl thompsongl left a comment

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🙌

I agree that the potentially negative scenarios cause little real concern.

@chandlerprall chandlerprall merged commit b1dd1f5 into elastic:master Jul 27, 2020
@chandlerprall chandlerprall deleted the bug/3379-sideeffects branch July 27, 2020 21:04
@clintandrewhall
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Bravo!! For anyone curious, this was the case that got caught within Kibana: elastic/kibana#72990

Our Shareable Runtime bundles up EUI with itself, (and I still want to figure out a better approach). But thankfully the bug was caught and fixed before 7.9 was released.

Thanks for the vigilant follow-up, @chandlerprall ...!

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@thompsongl thompsongl thompsongl approved these changes

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Reconsider sideEffects designation
4 participants
@chandlerprall @kibanamachine @clintandrewhall @thompsongl