Implements .env file support

[arcanis]

What's the problem this PR addresses?

A common need is to provide environment values into the environment via .env files. There's been a couple of issues and attempts at implementation already, which all were decently upvoted. I myself could have used it once or twice 😄

Props to @jj811208 for his implementation in #4835 - I wanted to make the configuration a little more generic (allowing to have multiple environment files, and to possibly disable it altogether), but it was a appreciated start.

Fixes #4718
Closes #4835 (Supercedes it)

How did you fix it?

A new setting, injectEnvironmentFiles, lets you define files that Yarn will load and inject into all scripts. It only affects subprocesses - Yarn itself still uses process.env for its checks, so you can't for example set YARN_* values and expect them to be applied to the current process (use the yarnrc file for that instead).

The injectEnvironmentFiles setting has a few properties:

• It defaults to .env
• Nothing will be injected if it's set to an empty array or null
• The paths inside may be suffixed by ? - in that case, Yarn won't throw if the file doesn't exist

The idea with this last property is to allow for simple user configuration (imagine, with the example below, that the project also has a gitignore with .env.*):

injectEnvironmentFiles:
  - .env
  - .env.${USER}?

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.

• I will check that all automated PR checks pass before the PR gets reviewed.

[daniluk4000]

Will this allow to use any variables from .env in .yarnrc.yml?

For example:

injectEnvironmentFiles:
  - .env

npmScopes:
  myScope:
    npmAlwaysAuth: true
    npmAuthToken: "${NPM_TOKEN:-}" #From .env
    npmRegistryServer: "https://customgitlab/api/v4/packages/npm"

[arcanis]

I forgot to add a test case covering it but I think it should.

[belgattitude]

Nothing will be injected if it's set to an empty array or null

Worth to mention that

injectEnvironmentFiles: []  # <-- works
injectEnvironmentFiles: null # <-- Internal Error: ENOENT: no such file or directory, open '/home/sebastien/github/nextjs-monorepo-example/null'

[belgattitude]

Added some concerns here: #5544 (comment)

Myself I'd recommend to make it 'opt-in'. It will create issues with few projects (ie nextjs...)

[hanzelkatomas]

May I ask which version will be this released?

[merceyz]

It will be in v4, you can use one of the release candidates if you want.

yarn set version canary

[lukeapage]

I was trying it out, thanks. Its worth noting that if you specify a env file that does not exist, you get an error, which means the use-case of .env.user that is git ignored is bad dx (the user needs to create an empty env file in order to run yarn install)

[arcanis]

I was trying it out, thanks. Its worth noting that if you specify a env file that does not exist, you get an error, which means the use-case of .env.user that is git ignored is bad dx (the user needs to create an empty env file in order to run yarn install)

It doesn't error if you suffix the path with a question mark (ie .env.user? won't throw if .env.user is missing).

[lukeapage]

Perfect, thanks - that works.

I just discovered it also errors when I run the command to setup my editor

yarn dlx @yarnpkg/sdks vscode

Internal Error: ENOENT: no such file or directory, open 'C:\Users\xxxx\AppData\Local\Temp\xfs-e4f23b26\dlx-12060\.env'
Error: ENOENT: no such file or directory, open 'C:\Users\xxxx\AppData\Local\Temp\xfs-e4f23b26\dlx-12060\.env'

which must be a bug?

(edit - easy to work around by adding ?)

[SimpleCreations]

For anyone having trouble with using env variable substitution in injectEnvironmentFiles field itself, and finding this PR, I've opened a bug report here: #6679