[Bug] environment variables for CRA are omitted

[original001]

Describe the bug

Storybook overrides environment variables defined with prefix REACT_APP. Possibly, it overrides more variables, but I don't investigate it.

Steps to reproduce the behavior

1. Define any variable with REACT_APP prefix.
2. Run build-storybook
3. Open bundle in browser
4. Find place where webpack replace process.env with variable's object.
5. I don't see my variable in the list

Expected behavior

List of vars includes my extra REACT_APP variable

Screenshots and/or logs

After short investigation I found that preset override DefinePlugin of cra webpack.config in this line

Environment

• OS: MacOS Mojave
• Node.js version: v12.14.1
• NPM version: 6.13.4

Details

It works if I use .env file, but doesn't if I use cli

[generalov]

This probably due to mergePlugins function implementation. The function takes the first plugin definition into results. According to the order of plugins the function takes DefinePlugin from storybook and omits the definition produced by CRA webpack config.

Related:
storybookjs/storybook#4841
storybookjs/storybook#12270