From 6c61b07131d7942ac6d9a3eb4ff817135ef9e985 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C5=81ukasz=20Bajsarowicz?= <lukasz@lbajsarowicz.me>
Date: Mon, 13 Apr 2026 23:28:53 +0200
Subject: [PATCH] perf: cache resolved theme in Theme Resolver

Avoid redundant theme collection loading on repeated get() calls
within the same request.

Ref: magento/magento2#40721
---
 .../Magento/Theme/Model/Theme/Resolver.php    |  37 ++++--
 .../Test/Unit/Model/Theme/ResolverTest.php    | 120 ++++++++++++++++++
 2 files changed, 148 insertions(+), 9 deletions(-)

diff --git a/app/code/Magento/Theme/Model/Theme/Resolver.php b/app/code/Magento/Theme/Model/Theme/Resolver.php
index 2d52dc19b00f0..bc7a87c60459c 100644
--- a/app/code/Magento/Theme/Model/Theme/Resolver.php
+++ b/app/code/Magento/Theme/Model/Theme/Resolver.php
@@ -10,6 +10,16 @@
  */
 class Resolver implements \Magento\Framework\View\Design\Theme\ResolverInterface
 {
+    /**
+     * @var array
+     */
+    private $resolvedThemes = [];
+
+    /**
+     * @var bool[]
+     */
+    private $isThemeResolved = [];
+
     /**
      * @var \Magento\Framework\View\DesignInterface
      */
@@ -48,19 +58,28 @@ public function __construct(
     public function get()
     {
         $area = $this->appState->getAreaCode();
-        if ($this->design->getDesignTheme()->getArea() == $area || $this->design->getArea() == $area) {
-            return $this->design->getDesignTheme();
+        if ($this->isThemeResolved[$area] ?? false) {
+            return $this->resolvedThemes[$area];
         }
 
-        /** @var \Magento\Theme\Model\ResourceModel\Theme\Collection $themeCollection */
-        $themeCollection = $this->themeFactory->create();
-        $themeIdentifier = $this->design->getConfigurationDesignTheme($area);
-        if (is_numeric($themeIdentifier)) {
-            $result = $themeCollection->getItemById($themeIdentifier);
+        $designTheme = $this->design->getDesignTheme();
+        if (($designTheme && $designTheme->getArea() == $area) || $this->design->getArea() == $area) {
+            $result = $designTheme;
         } else {
-            $themeFullPath = $area . \Magento\Framework\View\Design\ThemeInterface::PATH_SEPARATOR . $themeIdentifier;
-            $result = $themeCollection->getThemeByFullPath($themeFullPath);
+            /** @var \Magento\Theme\Model\ResourceModel\Theme\Collection $themeCollection */
+            $themeCollection = $this->themeFactory->create();
+            $themeIdentifier = $this->design->getConfigurationDesignTheme($area);
+            if (is_numeric($themeIdentifier)) {
+                $result = $themeCollection->getItemById($themeIdentifier);
+            } else {
+                $themeFullPath = $area . \Magento\Framework\View\Design\ThemeInterface::PATH_SEPARATOR . $themeIdentifier;
+                $result = $themeCollection->getThemeByFullPath($themeFullPath);
+            }
         }
+
+        $this->resolvedThemes[$area] = $result;
+        $this->isThemeResolved[$area] = true;
+
         return $result;
     }
 }
diff --git a/app/code/Magento/Theme/Test/Unit/Model/Theme/ResolverTest.php b/app/code/Magento/Theme/Test/Unit/Model/Theme/ResolverTest.php
index 78caf14e9b046..b436fe3a5c40b 100644
--- a/app/code/Magento/Theme/Test/Unit/Model/Theme/ResolverTest.php
+++ b/app/code/Magento/Theme/Test/Unit/Model/Theme/ResolverTest.php
@@ -258,4 +258,124 @@ public function testGetByAreaWithOtherAreaAndNumericThemeId()
 
         $this->assertEquals($this->themeMock, $this->model->get());
     }
+
+    public function testGetCachesResolvedThemeByArea()
+    {
+        $this->designMock->expects(
+            $this->once()
+        )->method(
+            'getDesignTheme'
+        )->willReturn(
+            $this->themeMock
+        );
+        $this->designMock->expects(
+            $this->once()
+        )->method(
+            'getArea'
+        )->willReturn(
+            'design_area'
+        );
+        $this->designMock->expects(
+            $this->once()
+        )->method(
+            'getConfigurationDesignTheme'
+        )->with(
+            'other_area'
+        )->willReturn(
+            'other_theme'
+        );
+
+        $this->themeMock->expects(
+            $this->once()
+        )->method(
+            'getArea'
+        )->willReturn(
+            'theme_area'
+        );
+
+        $this->themeCollectionFactoryMock->expects(
+            $this->once()
+        )->method(
+            'create'
+        )->willReturn(
+            $this->themeCollectionMock
+        );
+
+        $this->themeCollectionMock->expects(
+            $this->once()
+        )->method(
+            'getThemeByFullPath'
+        )->with(
+            'other_area' . ThemeInterface::PATH_SEPARATOR . 'other_theme'
+        )->willReturn(
+            $this->themeMock
+        );
+
+        $this->appStateMock->expects(
+            $this->exactly(2)
+        )->method(
+            'getAreaCode'
+        )->willReturn(
+            'other_area'
+        );
+
+        $this->assertSame($this->themeMock, $this->model->get());
+        $this->assertSame($this->themeMock, $this->model->get());
+    }
+
+    public function testGetCachesNullResolvedThemeByArea()
+    {
+        $this->designMock->expects(
+            $this->once()
+        )->method(
+            'getDesignTheme'
+        )->willReturn(
+            null
+        );
+        $this->designMock->expects(
+            $this->once()
+        )->method(
+            'getArea'
+        )->willReturn(
+            'design_area'
+        );
+        $this->designMock->expects(
+            $this->once()
+        )->method(
+            'getConfigurationDesignTheme'
+        )->with(
+            'other_area'
+        )->willReturn(
+            12
+        );
+
+        $this->themeCollectionFactoryMock->expects(
+            $this->once()
+        )->method(
+            'create'
+        )->willReturn(
+            $this->themeCollectionMock
+        );
+
+        $this->themeCollectionMock->expects(
+            $this->once()
+        )->method(
+            'getItemById'
+        )->with(
+            12
+        )->willReturn(
+            null
+        );
+
+        $this->appStateMock->expects(
+            $this->exactly(2)
+        )->method(
+            'getAreaCode'
+        )->willReturn(
+            'other_area'
+        );
+
+        $this->assertNull($this->model->get());
+        $this->assertNull($this->model->get());
+    }
 }