feature #28858 [DI] Deprecated using env vars with cannotBeEmpty() (ro0NL)

This PR was squashed before being merged into the 4.3-dev branch (closes #28858).

Discussion
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[DI] Deprecated using env vars with cannotBeEmpty()

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes-ish
| New feature?  | yes
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | yes
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #28827
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

Continuation of #28838 for 4.2

Using environment variables for nodes marked `cannotBeEmpty()` is semantically not possible, we'll never know the value is empty yes/no during compile time. Neither we should assume one or another.

Commits
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397c19ee5f [DI] Deprecated using env vars with cannotBeEmpty()

Author: nicolas-grekas

Tests/Compiler/ValidateEnvPlaceholdersPassTest.php

@@ -211,6 +211,38 @@ public function testEmptyEnvWhichCannotBeEmptyForScalarNode(): void
         $this->assertSame($expected, $container->resolveEnvPlaceholders($ext->getConfig()));
     }
 
+    /**
+     * NOT LEGACY (test exception in 5.0).
+     *
+     * @group legacy
+     * @expectedDeprecation Setting path "env_extension.scalar_node_not_empty_validated" to an environment variable is deprecated since Symfony 4.2. Remove "cannotBeEmpty()", "validate()" or include a prefix/suffix value instead.
+     */
+    public function testEmptyEnvWhichCannotBeEmptyForScalarNodeWithValidation(): void
+    {
+        $container = new ContainerBuilder();
+        $container->registerExtension($ext = new EnvExtension());
+        $container->prependExtensionConfig('env_extension', $expected = array(
+            'scalar_node_not_empty_validated' => '%env(SOME)%',
+        ));
+
+        $this->doProcess($container);
+
+        $this->assertSame($expected, $container->resolveEnvPlaceholders($ext->getConfig()));
+    }
+
+    public function testPartialEnvWhichCannotBeEmptyForScalarNode(): void
+    {
+        $container = new ContainerBuilder();
+        $container->registerExtension($ext = new EnvExtension());
+        $container->prependExtensionConfig('env_extension', $expected = array(
+            'scalar_node_not_empty_validated' => 'foo %env(SOME)% bar',
+        ));
+
+        $this->doProcess($container);
+
+        $this->assertSame($expected, $container->resolveEnvPlaceholders($ext->getConfig()));
+    }
+
     public function testEnvWithVariableNode(): void
     {
         $container = new ContainerBuilder();
@@ -282,6 +314,14 @@ public function getConfigTreeBuilder()
             ->children()
                 ->scalarNode('scalar_node')->end()
                 ->scalarNode('scalar_node_not_empty')->cannotBeEmpty()->end()
+                ->scalarNode('scalar_node_not_empty_validated')
+                    ->cannotBeEmpty()
+                    ->validate()
+                        ->always(function ($value) {
+                            return $value;
+                        })
+                    ->end()
+                ->end()
                 ->integerNode('int_node')->end()
                 ->floatNode('float_node')->end()
                 ->booleanNode('bool_node')->end()