* - [x] Upgrade to webpack 4.8.X
- [x] Utilize webpack 4 development and production modes
- [x] Upgrade webpack dev server
- [x] Webpack 4 compatible release of thread-loader
- [x] Webpack 4 compatible release of HtmlWebpackPlugin
- [x] Webpack 4 compatible release of SwPrecacheWebpackPlugin
- [x] Webpack 4 compatible release of WebpackManifestPlugin
- [x] Update README
- [x] Update WebpackDevServerUtils
- [x] Update InterpolateHtmlPlugin
- [x] Update ModuleScopePlugin
- [x] Update WatchMissingNodeModulesPlugin
- [x] Move UglifyJS options to webpack 4 optimize
- [x] Move InterpolateHtmlPlugin to make it tapable on HtmlWebpackPlugin
- [x] vendor splitting via splitChunks.splitChunks (https://twitter.com/wSokra/status/969633336732905474)
- [x] long term caching via splitChunks.runtimeChunk (https://twitter.com/wSokra/status/969679223278505985)
- [x] Make sure process.env.NODE_ENV is proxied correctly to `react-error-overlay`
- [x] Implicit webpack.NamedModulesPlugin in dev config as its default in webpack 4
- [x] Disable webpack performance hints as we have our own filesize reporter
- [x] Replace ExtractTextPlugin with MiniCssExtractPlugin
- [x] Switch to css whole file minification via OptimizeCSSAssetsPlugin rather than per module css minification to gain performance

* disable module concatenation

* fix cleanup

* fix optimization

* restore tmp removal

* preserve

* fix css tests

* fix test run

* fix svg test

* revert tmp dir

* fix import

* fix import

* help debugging

* fix tests

* fix sass test

* restore cleanup

- [x] Utilize webpack 4 development and production modes
- [x] Upgrade webpack dev server
- [x] Webpack 4 compatible release of thread-loader
- [x] Webpack 4 compatible release of HtmlWebpackPlugin
- [x] Webpack 4 compatible release of SwPrecacheWebpackPlugin
- [x] Webpack 4 compatible release of WebpackManifestPlugin
- [x] Update README
- [x] Update WebpackDevServerUtils
- [x] Update InterpolateHtmlPlugin
- [x] Update ModuleScopePlugin
- [x] Update WatchMissingNodeModulesPlugin
- [x] Move UglifyJS options to webpack 4 optimize
- [x] Move InterpolateHtmlPlugin to make it tapable on HtmlWebpackPlugin
- [x] vendor splitting via splitChunks.splitChunks (https://twitter.com/wSokra/status/969633336732905474)
- [x] long term caching via splitChunks.runtimeChunk (https://twitter.com/wSokra/status/969679223278505985)
- [x] Make sure process.env.NODE_ENV is proxied correctly to `react-error-overlay`
- [x] Implicit webpack.NamedModulesPlugin in dev config as its default in webpack 4
- [x] Disable webpack performance hints as we have our own filesize reporter
- [x] Replace ExtractTextPlugin with MiniCssExtractPlugin
- [x] Switch to css whole file minification via OptimizeCSSAssetsPlugin rather than per module css minification to gain performance

* Update svgr to 1.9.2 in order to reduce install size

Update babel-plugin-macros to 2.2.1.

Summary:
The `hasSlash` method uses `path.substr(path, path.length - 1)` to
remove the last character from `path`. Clearly, the first parameter is
suspect; it should be `0`. The code works as written, but only very
accidentally: the first parameter is coerced by `ToNumber` to `NaN`,
which is then coerced by `ToInteger` to `+0`, per [the spec][1].

[1]: https://www.ecma-international.org/ecma-262/6.0/#sec-string.prototype.substr

Test Plan:
Reading the spec should be sufficient. To verify in the Real World:
```js
const path = "has-slash-but-does-not-need-slash/"
const a = path.substr(path, path.length - 1);
const b = path.substr(0, path.length - 1);
console.log(a === b);  // true
console.log(a);        // has-slash-but-does-not-need-slash
```

wchargin-branch: ensureslash-accidental-coercion

* Update getCSSModuleLocalIdent to support Sass

* Fix Sass/SCSS index module tests

Also make them more consistent with the non-index variants.

* fix: update envinfo + implementation, update issue_template

* update envinfo to 5.4.0, add IE and Edge to —info command,

* Update sass-loader (#4363)

* Added bootstrap scss test (#4376)

* Support package distribution tags (#4348)

* Remove redundand variable check in `getInstallPackage`

* Simplify react-scripts version using `--scripts-version=@tagname` notation

* Add dist-tag tests to e2e-installs

* Updated jest version.

* Installs and adds sass loader task in webpack for dev environment.

* Uses Timer's branch of sass-loader without node-sass dependency.

* Adds method for handling SASS modules.

* Fixes extension of excluded files when looking for scss modules.

* Adds support for both .scss and .sass extensions.

* Uses ExtractTextPlugin with sass-loader to bundle styles for the production build.

* Bundles SASS modules for the production build.

* Uses the latest version of sass-loader.

* Adds function to create different rules for style loaders in dev environment.

* Abstracts style loaders to a common function to avoid repetition.

* Simplifies the common function that creates style loaders.

* Creates assets for testing SASS/SCSS support.

* Creates mock components and unit tests for SASS and SCSS with and without modules.

* Creates integration tests for SASS/SCSS support.

* Adds node-sass as a template dependency so sass-loader can be tested.

* Includes sass tests when test component is mounted.

* Fixes asserted module name for sass and scss modules tests.

* Removes tests against css imports in SCSS and SASS files.

* Updates sass-loader to v7.

* Uses getCSSModuleLocalIdent from react-dev-utils.

* Fixes tests to match the use of getCSSModuleLocalIdent.

* Improves readability of getStyleLoader function.

* Uses postcss after sass.

* Refactors dev config to simplify common function for style loaders.

* Refactors prod config to simplify common function for style loaders.

* Use importLoaders config according to css-loader docs.

Learnstorybook is a tutorial for Storybook that both uses CRA and is at a level of introductionary detail appropriate for CRA users.

* Docs - Document multiple build environments via

* Docs - Document multiple build environments via

* Docs - Document multiple build environments via

* Docs - Document multiple build environments via env-cmd

* fix - based upon requests

* Update README.md

* Update CSS Modules localIndetName

* Add missing file to package

* Correct regex

* plz plz plz

* Enable loose mode for `class-properties`

* Update comment to point to discussion

Resolves #4263 

Add troubleshooting for an issue that has to do with either 2FA, or using Windows, or both, when trying to deploy an app via gh-pages

* use the lastest url of gitignore file

* Update gitignore

* Revert to use ecma 5 in uglifyOptions

* remove explicit ecma version from uglifyOptions settings

The defaults are already what we want

* be explicit of where we use ecma: 8 and ecma: 5

* add `create-react-app --help` info for local file path --scripts-version

* make example path `../my-react-scripts` for local file path --help info

This reverts commit 1dcb3db3.

* allow appSrc accepting an array

* fixture of finding all appSrcs logic

* update docs on ModuleScopePlugin accepts an array for appSrc

* minor typo fix in docs: change directory to directories.