[!!!][FEATURE] Boolean and Null literals (#949)

This patch enhances Fluid's capabilities of dealing with booleans and null significantly.
Previously, the actual booleans `false` and `true` could be only created from within inline
syntax or if a ViewHelper argument was defined as boolean (in which case strings were
parsed as boolean). `null` values couldn't really be created at all. Now, there exist
standard variables for true, false, and null, which can be used in all contexts.

This patch is marked as breaking because it disallows the usage of the variable names
`true`, `false` and `null` in variable providers.

src/Core/Parser/SyntaxTree/ObjectAccessorNode.php

@@ -62,29 +62,42 @@ public function getObjectPath(): string
      */
     public function evaluate(RenderingContextInterface $renderingContext): mixed
     {
-        $objectPath = strtolower($this->objectPath);
         $variableProvider = $renderingContext->getVariableProvider();
-        if ($objectPath === '_all') {
-            return $variableProvider->getAll();
-        }
-        return $variableProvider->getByPath($this->objectPath);
+        return match (strtolower($this->objectPath)) {
+            '_all' => $variableProvider->getAll(),
+            'true' => true,
+            'false' => false,
+            'null' => null,
+            default => $variableProvider->getByPath($this->objectPath),
+        };
     }
 
     public function convert(TemplateCompiler $templateCompiler): array
     {
-        $path = $this->objectPath;
-        if ($path === '_all') {
-            return [
+        return match (strtolower($this->objectPath)) {
+            '_all' => [
                 'initialization' => '',
                 'execution' => '$renderingContext->getVariableProvider()->getAll()',
-            ];
-        }
-        return [
-            'initialization' => '',
-            'execution' => sprintf(
-                '$renderingContext->getVariableProvider()->getByPath(\'%s\')',
-                $path,
-            ),
-        ];
+            ],
+            'true' => [
+                'initialization' => '',
+                'execution' => 'true',
+            ],
+            'false' => [
+                'initialization' => '',
+                'execution' => 'false',
+            ],
+            'null' => [
+                'initialization' => '',
+                'execution' => 'null',
+            ],
+            default => [
+                'initialization' => '',
+                'execution' => sprintf(
+                    '$renderingContext->getVariableProvider()->getByPath(\'%s\')',
+                    $this->objectPath,
+                ),
+            ],
+        };
     }
 }

src/Core/Variables/InvalidVariableIdentifierException.php

@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file belongs to the package "TYPO3 Fluid".
+ * See LICENSE.txt that was shipped with this package.
+ */
+
+namespace TYPO3Fluid\Fluid\Core\Variables;
+
+class InvalidVariableIdentifierException extends \Exception {}

src/Core/Variables/StandardVariableProvider.php

@@ -14,6 +14,8 @@
  */
 class StandardVariableProvider implements VariableProviderInterface
 {
+    protected array $disallowedIdentifiers = ['null', 'true', 'false', '_all'];
+
     /**
      * Variables stored in context
      *
@@ -75,6 +77,9 @@ public function getAll(): array|\ArrayAccess
      */
     public function add(string $identifier, mixed $value): void
     {
+        if (in_array(strtolower($identifier), $this->disallowedIdentifiers)) {
+            throw new InvalidVariableIdentifierException('Invalid variable identifier: ' . $identifier, 1723131119);
+        }
         $this->variables[$identifier] = $value;
     }
 

tests/Unit/Core/Parser/SyntaxTree/ObjectAccessorNodeTest.php

@@ -28,6 +28,9 @@ public static function getEvaluateTestValues(): array
             [['foo' => ['bar' => 'test'], 'dynamic' => 'bar'], 'foo.{dynamic}', 'test'],
             [['foo' => ['bar' => 'test'], 'dynamic' => ['sub' => 'bar']], 'foo.{dynamic.sub}', 'test'],
             [['foo' => ['bar' => 'test'], 'dynamic' => ['sub' => 'bar'], 'baz' => 'sub'], 'foo.{dynamic.{baz}}', 'test'],
+            [[], 'true', true],
+            [[], 'false', false],
+            [[], 'null', null],
         ];
     }
 
@@ -43,7 +46,7 @@ public function testEvaluateGetsExpectedValue(array $variables, string $path, $e
         $variableContainer = new StandardVariableProvider($variables);
         $renderingContext->expects(self::any())->method('getVariableProvider')->willReturn($variableContainer);
         $value = $node->evaluate($renderingContext);
-        self::assertEquals($expected, $value);
+        self::assertSame($expected, $value);
     }
 
     #[Test]

tests/Unit/Core/Variables/StandardVariableProviderTest.php

@@ -12,6 +12,7 @@
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
+use TYPO3Fluid\Fluid\Core\Variables\InvalidVariableIdentifierException;
 use TYPO3Fluid\Fluid\Core\Variables\StandardVariableProvider;
 use TYPO3Fluid\Fluid\Tests\Unit\Core\Variables\Fixtures\StandardVariableProviderModelFixture;
 
@@ -434,4 +435,13 @@ public function getByPathReturnsExpectedValues(array $variables, string $path, $
         $result = $subject->getByPath($path);
         self::assertEquals($expected, $result);
     }
+
+    #[Test]
+    public function exceptionIsThrownForInvalidVariableIdentifier(): void
+    {
+        self::expectException(InvalidVariableIdentifierException::class);
+        self::expectExceptionCode(1723131119);
+        $subject = new StandardVariableProvider();
+        $subject->add('TrUe', false);
+    }
 }