magento/magento2#39959 catalog_product_save_before observer throws date-related error when using REST API without store-level values (getFinalPrice() issue)

app/code/Magento/Catalog/Observer/SetSpecialPriceStartDate.php

@@ -39,7 +39,14 @@ public function execute(\Magento\Framework\Event\Observer $observer)
         /** @var  $product \Magento\Catalog\Model\Product */
         $product = $observer->getEvent()->getProduct();
         if ($product->getSpecialPrice() && $product->getSpecialFromDate() === null) {
-            $product->setData('special_from_date', $this->localeDate->date()->setTime(0, 0));
+            // Set the special_from_date to the current date with time 00:00:00 when a special price is defined
+            // but no start date is specified. This ensures the special price takes effect immediately
+            // and is consistent with how the special price validation works in Magento.
+            // The time is explicitly set to midnight to ensure the special price is active for the entire day.
+            $product->setData(
+                'special_from_date',
+                $this->localeDate->date()->setTime(0, 0)->format('Y-m-d H:i:s')
+            );
         }
         return $this;
     }

app/code/Magento/Catalog/Test/Unit/Observer/SetSpecialPriceStartDateTest.php

@@ -88,13 +88,13 @@ protected function setUp(): void
     }
 
     /**
-     * Test observer execute method
+     * Test observer execute method when special_from_date is null
      */
     public function testExecuteModifySpecialFromDate(): void
     {
         $specialPrice = 15;
         $specialFromDate = null;
-        $localeDateMock = ['special_from_date' => $this->returnValue($this->dateObject)];
+        $formattedDate = '2023-01-01 00:00:00';
 
         $this->observerMock
             ->expects($this->once())
@@ -106,10 +106,18 @@ public function testExecuteModifySpecialFromDate(): void
             ->method('getProduct')
             ->willReturn($this->productMock);
 
-        $this->dateObject->expects($this->any())
+        $this->dateObject
+            ->expects($this->once())
             ->method('setTime')
+            ->with(0, 0)
             ->willReturnSelf();
 
+        $this->dateObject
+            ->expects($this->once())
+            ->method('format')
+            ->with('Y-m-d H:i:s')
+            ->willReturn($formattedDate);
+
         $this->timezone
             ->expects($this->once())
             ->method('date')
@@ -128,7 +136,79 @@ public function testExecuteModifySpecialFromDate(): void
         $this->productMock
             ->expects($this->once())
             ->method('setData')
-            ->willReturn($localeDateMock);
+            ->with('special_from_date', $formattedDate);
+
+        $this->observer->execute($this->observerMock);
+    }
+
+    /**
+     * Test observer doesn't modify special_from_date when it's already set
+     */
+    public function testExecuteDoesNotModifyExistingSpecialFromDate(): void
+    {
+        $specialPrice = 15;
+        $existingSpecialFromDate = '2023-01-01 00:00:00';
+
+        $this->observerMock
+            ->expects($this->once())
+            ->method('getEvent')
+            ->willReturn($this->eventMock);
+
+        $this->eventMock
+            ->expects($this->once())
+            ->method('getProduct')
+            ->willReturn($this->productMock);
+
+        $this->productMock
+            ->expects($this->once())
+            ->method('getSpecialPrice')
+            ->willReturn($specialPrice);
+
+        $this->productMock
+            ->expects($this->once())
+            ->method('getSpecialFromDate')
+            ->willReturn($existingSpecialFromDate);
+
+        $this->productMock
+            ->expects($this->never())
+            ->method('setData');
+
+        $this->timezone
+            ->expects($this->never())
+            ->method('date');
+
+        $this->observer->execute($this->observerMock);
+    }
+
+    /**
+     * Test observer doesn't set special_from_date when special price is not set
+     */
+    public function testExecuteDoesNotSetSpecialFromDateWithoutSpecialPrice(): void
+    {
+        $specialPrice = null;
+
+        $this->observerMock
+            ->expects($this->once())
+            ->method('getEvent')
+            ->willReturn($this->eventMock);
+
+        $this->eventMock
+            ->expects($this->once())
+            ->method('getProduct')
+            ->willReturn($this->productMock);
+
+        $this->productMock
+            ->expects($this->once())
+            ->method('getSpecialPrice')
+            ->willReturn($specialPrice);
+
+        $this->productMock
+            ->expects($this->never())
+            ->method('getSpecialFromDate');
+
+        $this->productMock
+            ->expects($this->never())
+            ->method('setData');
 
         $this->observer->execute($this->observerMock);
     }

dev/tests/integration/testsuite/Magento/Catalog/Model/Product/SpecialPriceTest.php

@@ -0,0 +1,116 @@
+<?php
+/**
+ * Copyright 2025 Adobe
+ * * All Rights Reserved.
+ */
+declare(strict_types=1);
+
+namespace Magento\Catalog\Model\Product;
+
+use Magento\Catalog\Api\ProductRepositoryInterface;
+use Magento\Framework\App\ObjectManager;
+use Magento\Framework\ObjectManagerInterface;
+use Magento\Framework\Stdlib\DateTime\TimezoneInterface;
+use Magento\TestFramework\Helper\Bootstrap;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Integration test for special price functionality
+ */
+class SpecialPriceTest extends TestCase
+{
+    /**
+     * @var ObjectManager
+     */
+    private ObjectManager $objectManager;
+
+    /**
+     * @var ProductRepositoryInterface
+     */
+    private mixed $productRepository;
+
+    /**
+     * @var TimezoneInterface
+     */
+    private mixed $localeDate;
+
+    /**
+     * Set up
+     */
+    protected function setUp(): void
+    {
+        $this->objectManager = Bootstrap::getObjectManager();
+        $this->productRepository = $this->objectManager->get(ProductRepositoryInterface::class);
+        $this->localeDate = $this->objectManager->get(TimezoneInterface::class);
+    }
+
+    /**
+     * Test that special_from_date is automatically set when special price is set via API
+     *
+     * @magentoDbIsolation enabled
+     * @magentoAppIsolation enabled
+     * @magentoDataFixture Magento/Catalog/_files/product_simple.php
+     */
+    public function testSpecialFromDateSetWhenSpecialPriceSet(): void
+    {
+        $product = $this->productRepository->get('simple');
+        $product->setSpecialPrice(5.99);
+        $product->setSpecialFromDate(null);
+
+        $this->productRepository->save($product);
+        $updatedProduct = $this->productRepository->get('simple', false, null, true);
+        $this->assertNotNull($updatedProduct->getSpecialFromDate());
+        $expectedDate = $this->localeDate->date()->setTime(0, 0, 0)->format('Y-m-d');
+        $actualDate = substr($updatedProduct->getSpecialFromDate(), 0, 10);
+
+        // Assert special_from_date is set to current date with time 00:00:00
+        $this->assertEquals($expectedDate, $actualDate);
+    }
+
+    /**
+     * Test that existing special_from_date is not changed when product is saved
+     *
+     * @magentoDbIsolation enabled
+     * @magentoAppIsolation enabled
+     * @magentoDataFixture Magento/Catalog/_files/product_simple.php
+     */
+    public function testExistingSpecialFromDateNotChanged(): void
+    {
+        $product = $this->productRepository->get('simple');
+
+        $specificDate = '2023-01-01 00:00:00';
+        $product->setSpecialPrice(5.99);
+        $product->setSpecialFromDate($specificDate);
+
+        $this->productRepository->save($product);
+        $updatedProduct = $this->productRepository->get('simple', false, null, true);
+
+        // Assert special_from_date remains unchanged
+        $this->assertEquals($specificDate, $updatedProduct->getSpecialFromDate());
+    }
+
+    /**
+     * Test that special price is correctly applied when special_from_date is today
+     *
+     * @magentoDbIsolation enabled
+     * @magentoAppIsolation enabled
+     * @magentoDataFixture Magento/Catalog/_files/product_simple.php
+     */
+    public function testSpecialPriceAppliedWithTodayDate(): void
+    {
+        $product = $this->productRepository->get('simple');
+        $regularPrice = 10.00;
+        $specialPrice = 5.99;
+
+        $product->setPrice($regularPrice);
+        $today = $this->localeDate->date()->format('Y-m-d 00:00:00');
+        $product->setSpecialPrice($specialPrice);
+        $product->setSpecialFromDate($today);
+
+        $this->productRepository->save($product);
+        $updatedProduct = $this->productRepository->get('simple', false, null, true);
+
+        // Assert special price is applied
+        $this->assertEquals($specialPrice, $updatedProduct->getFinalPrice());
+    }
+}