Description
In my .env file, I have a variable TEST that depends on the APP_ENV variable like this:

# .env file

###> symfony/framework-bundle ###
APP_ENV=dev
APP_SECRET=2eb810c79fba0dd5c029a2fa53bfdb51
###< symfony/framework-bundle ###

TEST=foo_${APP_ENV}

I run composer dump-env dev command to generate my .env.locale.php, everything works fine, the value of my variable TEST is correct.

// .env.locale.php

return array (
  'APP_ENV' => 'dev',
  'TEST' => 'foo_dev',
  'APP_SECRET' => '2eb810c79fba0dd5c029a2fa53bfdb51',
);

Then I run the same command with prod environment (composer dump-env prod), the value of TEST is wrong (it is same as for dev)

// .env.locale.php

return array (
  'APP_ENV' => 'prod',
  'TEST' => 'foo_dev',
  'APP_SECRET' => '2eb810c79fba0dd5c029a2fa53bfdb51',
);

But when I put my variable TEST before the APP_ENV like this:

# .env file

TEST=foo_${APP_ENV}

###> symfony/framework-bundle ###
APP_ENV=dev
APP_SECRET=2eb810c79fba0dd5c029a2fa53bfdb51
###< symfony/framework-bundle ###

And I run composer dump-env prod again, the value of TEST is correct

// .env.locale.php

return array (
  'APP_ENV' => 'prod',
  'TEST' => 'foo_prod',
  'APP_SECRET' => '2eb810c79fba0dd5c029a2fa53bfdb51',
);

How can we explain that ?

How to reproduce

• Create a new Symfony project composer create-project symfony/skeleton bug_app
• Add new variable TEST in your .env
• Run composer dump-env prod
• Take a look at .env.locale.php
• In your .env file, put your TEST variable before the APP_ENV
• Then run composer dump-env prod again
• Take a look at .env.locale.php again