[4.1 BC Break][DI] Env placeholder defaulting to float now rejected for scalar config node

[Majkl578]

Symfony version(s) affected: 4.1.0

Description
Symfony 4.1.0 introduced validation of env vars in #23888. This breaks env defaults defined as parameters directly in YAML config for seemingly incompatible types, i.e. env defaulting to float value while node is declared as scalarNode (float is scalar too btw).

In ValidateEnvPlaceholdersPass.php line 54:
                                                                                                              
  [Symfony\Component\DependencyInjection\Exception\LogicException]                                            
  Invalid type for env parameter "env(ABC)". Expected "string", but got "float".

How to reproduce

This is based on real configuration of SncRedisBundle which now suffers from this BC break.

Have a bundle with DI configuration having a scalar config node as such:

...
->arrayNode('options')
    ->children()
        ->scalarNode('profile')->defaultValue('default')

Then configured using YAML like this:

parameters:
    env(REDIS_PROFILE): 3.2

snc_redis:
    clients:
        default:
            type: predis
            alias: default
            dsn: '%env(REDIS_DSN)%'
            options:
                profile: '%env(REDIS_PROFILE)%'

Since options.profile is defined as scalarNode(), default value 3.2 (being a float) is rejected and exception above is thrown.

Additional context

Exception trace:
 Symfony\Component\DependencyInjection\Compiler\ValidateEnvPlaceholdersPass->process() at vendor/symfony/dependency-injection/Compiler/Compiler.php:95
 Symfony\Component\DependencyInjection\Compiler\Compiler->compile() at vendor/symfony/dependency-injection/ContainerBuilder.php:736
 Symfony\Component\DependencyInjection\ContainerBuilder->compile() at vendor/symfony/http-kernel/Kernel.php:513
 Symfony\Component\HttpKernel\Kernel->initializeContainer() at vendor/symfony/http-kernel/Kernel.php:125
 Symfony\Component\HttpKernel\Kernel->boot() at vendor/symfony/framework-bundle/Console/Application.php:64
 Symfony\Bundle\FrameworkBundle\Console\Application->doRun() at vendor/symfony/console/Application.php:143
 Symfony\Component\Console\Application->run() at bin/console:37

[ro0NL]

Gave it a quick look, and i think we can include all scalar types here:

symfony/src/Symfony/Component/DependencyInjection/Compiler/ValidateEnvPlaceholdersPass.php

Line 50 in c81f88f

$types = $envTypes[$prefix] ?? array('string');

As those types are in fact allowed as env parameter defaults (or only number|string i believe)

cc @nicolas-grekas

[ro0NL]

On the other side.. we can also deprecate non-string values here 🤔 as we imply a default string prefix (for envs being string values)

symfony/src/Symfony/Component/DependencyInjection/Compiler/ValidateEnvPlaceholdersPass.php

Line 49 in c81f88f

$prefix = (false === $i = strpos($env, ':')) ? 'string' : substr($env, 0, $i);

[nicolas-grekas]

We should not force ppl to be stricter than PHP's default mode. Let's follow the default coercion rules.