feature #19681 [DI] Allow injecting ENV parameters at runtime using %env(MY_ENV_VAR)% (nicolas-grekas)

This PR was merged into the 3.2-dev branch.

Discussion
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[DI] Allow injecting ENV parameters at runtime using %env(MY_ENV_VAR)%

| Q             | A
| ------------- | ---
| Branch?       | master
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |  #10138, #7555, #16403, #18155
| License       | MIT
| Doc PR        | symfony/symfony-docs#6918

This is an alternative approach to #18155 for injecting env vars into container configurations.

With this PR, anywhere parameters are allowed, one can use `%env(ENV_VAR)%` to inject a dynamic env var. Additionally, if one sets a value to such parameters in e.g. the `parameter.yml` file (`env(ENV_VAR): foo`), this value will be used as a default value when the env var is not defined. If no default value is specified, an `EnvVarNotFoundException` will be thrown at runtime.

Unlike previous attempts that also used parameters (#16403), the implementation is compatible with DI extensions: before being dumped, env vars are resolved to uniquely identifiable string placeholders that can get through DI extensions manipulations. When dumped, these unique placeholders are replaced by dynamic calls to a getEnv method..

ping @magnusnordlander @dzuelke @fabpot

Commits
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bac2132 [DI] Allow injecting ENV parameters at runtime using %env(MY_ENV_VAR)% syntax

Author: fabpot

Kernel.php

@@ -16,7 +16,6 @@
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Dumper\PhpDumper;
-use Symfony\Component\DependencyInjection\ParameterBag\ParameterBag;
 use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;
 use Symfony\Component\DependencyInjection\Loader\YamlFileLoader;
 use Symfony\Component\DependencyInjection\Loader\IniFileLoader;
@@ -611,7 +610,8 @@ protected function prepareContainer(ContainerBuilder $container)
      */
     protected function getContainerBuilder()
     {
-        $container = new ContainerBuilder(new ParameterBag($this->getKernelParameters()));
+        $container = new ContainerBuilder();
+        $container->getParameterBag()->add($this->getKernelParameters());
 
         if (class_exists('ProxyManager\Configuration') && class_exists('Symfony\Bridge\ProxyManager\LazyProxy\Instantiator\RuntimeInstantiator')) {
             $container->setProxyInstantiator(new RuntimeInstantiator());