[DependencyInjection] Add defined prefix for env var processor

src/Symfony/Component/DependencyInjection/CHANGELOG.md

@@ -5,6 +5,7 @@ CHANGELOG
 ---
 
  * Deprecate `ContainerAwareInterface` and `ContainerAwareTrait`, use dependency injection instead
+ * Add `defined` env var processor that returns `true` for defined and neither null nor empty env vars
 
 6.3
 ---

src/Symfony/Component/DependencyInjection/EnvVarProcessor.php

@@ -56,6 +56,7 @@ public static function getProvidedTypes(): array
             'require' => 'bool|int|float|string|array',
             'enum' => \BackedEnum::class,
             'shuffle' => 'array',
+            'defined' => 'bool',
         ];
     }
 
@@ -103,6 +104,14 @@ public function getEnv(string $prefix, string $name, \Closure $getEnv): mixed
             return $backedEnumClassName::tryFrom($backedEnumValue) ?? throw new RuntimeException(sprintf('Enum value "%s" is not backed by "%s".', $backedEnumValue, $backedEnumClassName));
         }
 
+        if ('defined' === $prefix) {
+            try {
+                return '' !== ($getEnv($name) ?? '');
+            } catch (EnvNotFoundException) {
+                return false;
+            }
+        }
+
         if ('default' === $prefix) {
             if (false === $i) {
                 throw new RuntimeException(sprintf('Invalid env "default:%s": a fallback parameter should be provided.', $name));

src/Symfony/Component/DependencyInjection/Tests/Compiler/RegisterEnvVarProcessorsPassTest.php

@@ -50,6 +50,7 @@ public function testSimpleProcessor()
             'require' => ['bool', 'int', 'float', 'string', 'array'],
             'enum' => [\BackedEnum::class],
             'shuffle' => ['array'],
+            'defined' => ['bool'],
         ];
 
         $this->assertSame($expected, $container->getParameterBag()->getProvidedTypes());

src/Symfony/Component/DependencyInjection/Tests/EnvVarProcessorTest.php

@@ -925,4 +925,21 @@ public function testGetEnvCastsNull($expected, string $prefix)
             });
         }));
     }
+
+    /**
+     * @dataProvider provideGetEnvDefined
+     */
+    public function testGetEnvDefined(bool $expected, callable $callback)
+    {
+        $this->assertSame($expected, (new EnvVarProcessor(new Container()))->getEnv('defined', 'NO_SOMETHING', $callback));
+    }
+
+    public static function provideGetEnvDefined(): iterable
+    {
+        yield 'Defined' => [true, fn () => 'foo'];
+        yield 'Falsy but defined' => [true, fn () => '0'];
+        yield 'Empty string' => [false, fn () => ''];
+        yield 'Null' => [false, fn () => null];
+        yield 'Env var not defined' => [false, fn () => throw new EnvNotFoundException()];
+    }
 }