Fix increasing & decreasing sale price in product bulk edit (#50842)

* Set the regular price when the `Change to:` price is left empty

* Avoid fatal error when price is empty

* Add changefile(s) from automation for the following project(s): woocommerce

* Avoid setting the price to 0 when there wasn't a previous sale

* Move the WC_Tests_Admin_Post_Types test to the appropiate folder so it's run

* Add e2e test

* Add e2e test

* Add changefile(s) from automation for the following project(s): woocommerce

* Add changefile(s) from automation for the following project(s): woocommerce

* Fix lint errors

* Fix lint errors

* Fix test

* Fix lint errors

* Revert mv

* Address increasing sale from 0

---------

Co-authored-by: github-actions <github-actions@github.com>

plugins/woocommerce/changelog/50842-43149-fix-bulk-product-price-in-de-crease

@@ -0,0 +1,4 @@
+Significance: minor
+Type: fix
+
+Product bulk edit: fix increasing & decreasing sale price when there was no previous sale.

plugins/woocommerce/includes/admin/class-wc-admin-post-types.php

@@ -896,7 +896,8 @@ class WC_Admin_Post_Types {
 			return false;
 		}
 
-		$old_price     = (float) $product->{"get_{$price_type}_price"}();
+		$old_price     = $product->{"get_{$price_type}_price"}();
+		$old_price     = '' === $old_price ? (float) $product->get_regular_price() : (float) $old_price;
 		$price_changed = false;
 
 		$change_price  = absint( $request_data[ "change_{$price_type}_price" ] );

plugins/woocommerce/tests/e2e-pw/tests/merchant/product-edit.spec.js

@@ -282,3 +282,119 @@ test(
 		} );
 	}
 );
+
+test(
+	'can decrease the sale price if the product was not previously in sale when bulk editing products',
+	{ tag: [ '@gutenberg', '@services' ] },
+	async ( { page, products } ) => {
+		await page.goto( `wp-admin/edit.php?post_type=product` );
+
+		const salePriceDecrease = 10;
+
+		await test.step( 'Update products with the "Sale > Decrease existing sale price" option', async () => {
+			await page.goto( `wp-admin/edit.php?post_type=product` );
+
+			for ( const product of products ) {
+				await page.getByLabel( `Select ${ product.name }` ).click();
+			}
+
+			await page
+				.locator( '#bulk-action-selector-top' )
+				.selectOption( 'Edit' );
+			await page.locator( '#doaction' ).click();
+
+			await page
+				.locator( 'select[name="change_sale_price"]' )
+				.selectOption(
+					'Decrease existing sale price by (fixed amount or %):'
+				);
+			await page
+				.getByPlaceholder( 'Enter sale price ($)' )
+				.fill( `${ salePriceDecrease }%` );
+
+			await page.getByRole( 'button', { name: 'Update' } ).click();
+		} );
+
+		await test.step( 'Verify products have a sale price', async () => {
+			for ( const product of products ) {
+				await page.goto( `product/${ product.slug }` );
+
+				const expectedSalePrice = (
+					product.regular_price *
+					( 1 - salePriceDecrease / 100 )
+				).toFixed( 2 );
+
+				await expect
+					.soft(
+						await page
+							.locator( 'ins' )
+							.getByText( `$${ expectedSalePrice }` )
+							.count()
+					)
+					.toBeGreaterThan( 0 );
+			}
+		} );
+	}
+);
+
+test(
+	'increasing the sale price from 0 does not change the sale price when bulk editing products',
+	{ tag: [ '@gutenberg', '@services' ] },
+	async ( { page, api } ) => {
+		let product;
+		await api
+			.post( 'products', {
+				id: 0,
+				name: `Product _${ Date.now() }`,
+				type: 'simple',
+				regular_price: '100',
+				sale_price: '0',
+				manage_stock: true,
+				stock_quantity: 10,
+				stock_status: 'instock',
+			} )
+			.then( ( response ) => {
+				product = response.data;
+			} );
+
+		const salePriceIncrease = 10;
+
+		await test.step( 'Update products with the "Sale > Increase existing sale price" option', async () => {
+			await page.goto( `wp-admin/edit.php?post_type=product` );
+
+			await page.getByLabel( `Select ${ product.name }` ).click();
+
+			await page
+				.locator( '#bulk-action-selector-top' )
+				.selectOption( 'Edit' );
+			await page.locator( '#doaction' ).click();
+
+			await page
+				.locator( 'select[name="change_sale_price"]' )
+				.selectOption(
+					'Increase existing sale price by (fixed amount or %):'
+				);
+
+			await page
+				.getByPlaceholder( 'Enter sale price ($)' )
+				.fill( `${ salePriceIncrease }%` );
+
+			await page.getByRole( 'button', { name: 'Update' } ).click();
+		} );
+
+		await test.step( 'Verify products have a sale price', async () => {
+			await page.goto( `product/${ product.slug }` );
+
+			const expectedSalePrice = '$0.00';
+
+			await expect
+				.soft(
+					await page
+						.locator( 'ins' )
+						.getByText( expectedSalePrice )
+						.count()
+				)
+				.toBeGreaterThan( 0 );
+		} );
+	}
+);