Fix regression bug for duplicate block rendering with getSortedChildren() (#4480)

* Fix regression bug for duplicate block rendering with getSortedChildren()

* Fix code formatting via php-cs

---------

Co-authored-by: Sven Reichel <github-sr@hotmail.com>

Author: bucha

app/code/core/Mage/Core/Block/Abstract.php

@@ -465,7 +465,6 @@ public function setChild($alias, $block)
 
         $block->setParentBlock($this);
         $block->setBlockAlias($alias);
-        $this->unsetChild($alias);
         $this->_children[$alias] = $block;
         return $this;
     }
@@ -705,6 +704,11 @@ public function insert($block, $siblingName = '', $after = false, $alias = '')
             $this->setChild($name, $block);
         }
 
+        $existingKey = array_search($name, $this->_sortedChildren);
+        if ($existingKey !== false) {
+            array_splice($this->_sortedChildren, $existingKey, 1);
+        }
+
         if ($siblingName === '') {
             if ($after) {
                 $this->_sortedChildren[] = $name;

tests/unit/Mage/Core/Block/Text/ListTest.php

@@ -90,14 +90,33 @@ public function testUniqueBlockNameOrdering(): void
         $parentBlock->insert($childBlockC, 'child_b', true);
 
         $childBlockA = $layout->createBlock('core/text', 'child_a')->setText('A');
-        $parentBlock->insert($childBlockC, 'child_b', false);
+        $parentBlock->insert($childBlockA, 'child_b', false);
 
         $childBlockB = $layout->createBlock('core/text', 'child_b')->setText('B');
-        $parentBlock->insert($childBlockC, 'child_a', true);
+        $parentBlock->insert($childBlockB, 'child_a', true);
 
         $parentBlock->unsetChild('child_a');
         $parentBlock->unsetChild('child_b');
 
         $this->assertSame('CD', $parentBlock->toHtml());
     }
+
+    public function testSortInstructionsAfterReplaceChild()
+    {
+        $layout = Mage::getModel('core/layout');
+
+        $parentBlock = $layout->createBlock('core/text_list', 'parent');
+
+        $childBlockA = $layout->createBlock('core/text', 'target_block')->setText('A');
+        $parentBlock->insert($childBlockA, '', false, 'child');
+
+        $childBlockB = $layout->createBlock('core/text', 'target_block')->setText('B');
+
+        // Replacing the block but keeping its order within the parent
+        $layout->unsetBlock('target_block');
+        $layout->setBlock('target_block', $childBlockB);
+        $parentBlock->setChild('child', $childBlockB);
+
+        $this->assertSame('B', $parentBlock->toHtml());
+    }
 }