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.

* Add explicit dep on plugin-proposal-object-rest-spread to babel-preset-react-app

* Bump babel-related deps to beta.42

* Pass useBuiltIns directly to react-preset

the screencast for react storybook is non-free. Remove.

s/allows to easily makes/allows you to easily make/

This is the current node LTS release.