[BUGFIX] Explicitly set variables override local variables (#849)

Documentation/Usage/Syntax.rst

@@ -200,3 +200,15 @@ the scope:
         <f:variable name="lastItem" value="{item}" />
     </f:for>
     <!-- {lastItem} is "second" -->
+
+If a global variable is created inside a local scope and uses the same name as a local
+variable, it will still leak out of the scope and will also be valid inside the scope:
+
+.. code-block:: xml
+
+    <f:for each="{0: 'first', 1: 'second'}" as="item">
+        <!-- {item} is "first" or "second" -->
+        <f:variable name="item" value="overwritten" />
+        <!-- {item} is "overwritten" -->
+    </f:for>
+    <!-- {item} is "overwritten" -->

src/Core/Variables/ScopedVariableProvider.php

@@ -42,6 +42,7 @@ public function getLocalVariableProvider(): VariableProviderInterface
     public function add($identifier, $value): void
     {
         $this->globalVariables->add($identifier, $value);
+        $this->localVariables->add($identifier, $value);
     }
 
     /**

tests/Functional/ViewHelpers/ForViewHelperTest.php

@@ -178,6 +178,13 @@ public static function renderDataProvider(): \Generator
             'overwritten',
         ];
 
+        $value = ['bar', 2];
+        yield 'local variables can be converted to global variables inside loop' => [
+            '<f:for each="{value}" as="item">{item}|<f:variable name="item" value="overwritten" />{item}|</f:for>{item}',
+            ['value' => $value],
+            'bar|overwritten|2|overwritten|overwritten',
+        ];
+
         $value = ['bar', 2];
         yield 'variables set inside loop can be used after loop' => [
             '<f:for each="{value}" key="key" as="item"><f:variable name="foo" value="bar" /></f:for>{foo}',

tests/Unit/Core/Variables/ScopedVariableProviderTest.php

@@ -283,7 +283,7 @@ public function addVariable()
         $variableProvider = new ScopedVariableProvider(new StandardVariableProvider(), new StandardVariableProvider());
         $variableProvider->add('globalVar', 'global');
         self::assertEquals('global', $variableProvider->getGlobalVariableProvider()->get('globalVar'));
-        self::assertNull($variableProvider->getLocalVariableProvider()->get('globalVar'));
+        self::assertEquals('global', $variableProvider->getLocalVariableProvider()->get('globalVar'));
     }
 
     /**