From 4b3201c7036d09fdf5adae99c8fe48b2c6c0b45b Mon Sep 17 00:00:00 2001
From: Konstantin Obenland <obenland@gmx.de>
Date: Fri, 5 Dec 2025 11:54:40 -0600
Subject: [PATCH 1/2] Preserve whitespace inside pre elements when federating
 content

---
 includes/class-sanitize.php                   | 21 ++++++++
 includes/class-shortcodes.php                 |  2 +-
 includes/transformer/class-post.php           |  4 +-
 .../includes/transformer/class-test-post.php  | 48 +++++++++++++++++++
 4 files changed, 72 insertions(+), 3 deletions(-)

diff --git a/includes/class-sanitize.php b/includes/class-sanitize.php
index 092a2b7bf3..6f131c1b87 100644
--- a/includes/class-sanitize.php
+++ b/includes/class-sanitize.php
@@ -201,4 +201,25 @@ public static function content( $content ) {
 
 		return $content;
 	}
+
+	/**
+	 * Strip newlines, carriage returns, and tabs from content while preserving them inside pre elements.
+	 *
+	 * Code blocks require whitespace to be preserved for proper formatting.
+	 *
+	 * @param string $content The content to process.
+	 *
+	 * @return string The trimmed content with whitespace stripped except inside pre elements.
+	 */
+	public static function strip_whitespace( $content ) {
+		return \trim(
+			\preg_replace_callback(
+				'/(<pre[^>]*>.*?<\/pre>)|[\n\r\t]+/is',
+				static function ( $matches ) {
+					return $matches[1] ?? '';
+				},
+				$content
+			)
+		);
+	}
 }
diff --git a/includes/class-shortcodes.php b/includes/class-shortcodes.php
index 1554fa646d..609752a306 100644
--- a/includes/class-shortcodes.php
+++ b/includes/class-shortcodes.php
@@ -191,7 +191,7 @@ public static function content( $attributes, $content, $tag ) {
 		// Replace script and style elements.
 		$content = \preg_replace( '@<(script|style)[^>]*?>.*?</\\1>@si', '', $content );
 		$content = \strip_shortcodes( $content );
-		$content = \trim( \preg_replace( '/[\n\r\t]/', '', $content ) );
+		$content = Sanitize::strip_whitespace( $content );
 
 		add_shortcode( 'ap_content', array( 'Activitypub\Shortcodes', 'content' ) );
 
diff --git a/includes/transformer/class-post.php b/includes/transformer/class-post.php
index 6ff5aa3db0..92323ad391 100644
--- a/includes/transformer/class-post.php
+++ b/includes/transformer/class-post.php
@@ -12,6 +12,7 @@
 use Activitypub\Collection\Interactions;
 use Activitypub\Collection\Replies;
 use Activitypub\Model\Blog;
+use Activitypub\Sanitize;
 use Activitypub\Shortcodes;
 
 use function Activitypub\esc_hashtag;
@@ -539,8 +540,7 @@ protected function get_content() {
 		\wp_reset_postdata();
 
 		$content = \wpautop( $content );
-		$content = \preg_replace( '/[\n\r\t]/', '', $content );
-		$content = \trim( $content );
+		$content = Sanitize::strip_whitespace( $content );
 
 		// Don't need these anymore, should never appear in a post.
 		Shortcodes::unregister();
diff --git a/tests/phpunit/tests/includes/transformer/class-test-post.php b/tests/phpunit/tests/includes/transformer/class-test-post.php
index 6ea906bc77..fccaa7929c 100644
--- a/tests/phpunit/tests/includes/transformer/class-test-post.php
+++ b/tests/phpunit/tests/includes/transformer/class-test-post.php
@@ -1106,6 +1106,54 @@ public function test_get_post_content_template_with_scenarios( $post_data, $expe
 		$this->assertSame( $expected_template, $template, $description );
 	}
 
+	/**
+	 * Test that code blocks preserve newlines when content is transformed.
+	 *
+	 * @covers ::get_content
+	 */
+	public function test_code_blocks_preserve_newlines() {
+		$code_content = "function test() {\n\treturn true;\n}";
+		$post         = self::factory()->post->create_and_get(
+			array(
+				'post_title'   => 'Code Example',
+				'post_content' => '<pre>' . $code_content . '</pre>',
+				'post_status'  => 'publish',
+			)
+		);
+
+		$object  = Post::transform( $post )->to_object();
+		$content = $object->get_content();
+
+		// The pre block content should preserve newlines and tabs.
+		$this->assertStringContainsString( '<pre>', $content, 'Content should contain pre tag' );
+		$this->assertStringContainsString( "\n", $content, 'Content should preserve newlines inside pre blocks' );
+		$this->assertStringContainsString( "\t", $content, 'Content should preserve tabs inside pre blocks' );
+	}
+
+	/**
+	 * Test that regular content has whitespace stripped while code blocks are preserved.
+	 *
+	 * @covers ::get_content
+	 */
+	public function test_mixed_content_preserves_code_blocks() {
+		$post = self::factory()->post->create_and_get(
+			array(
+				'post_title'   => 'Mixed Content',
+				'post_content' => "<p>Regular paragraph</p>\n\n<pre class=\"code\">line1\nline2\nline3</pre>\n\n<p>Another paragraph</p>",
+				'post_status'  => 'publish',
+			)
+		);
+
+		$object  = Post::transform( $post )->to_object();
+		$content = $object->get_content();
+
+		// Pre block should preserve newlines.
+		$this->assertStringContainsString( "line1\nline2\nline3", $content, 'Pre block should preserve newlines' );
+
+		// Regular paragraphs should be joined without extra newlines.
+		$this->assertStringNotContainsString( "</p>\n\n<p>", $content, 'Paragraphs should not have newlines between them' );
+	}
+
 	/**
 	 * Data provider for get_post_content_template tests with various scenarios.
 	 *

From 833b95333199f99e47149e4fe4be2d633c1a4b96 Mon Sep 17 00:00:00 2001
From: Automattic Bot <sysops+ghmatticbot@automattic.com>
Date: Fri, 5 Dec 2025 18:56:02 +0100
Subject: [PATCH 2/2] Add changelog

---
 .github/changelog/2595-from-description | 4 ++++
 1 file changed, 4 insertions(+)
 create mode 100644 .github/changelog/2595-from-description

diff --git a/.github/changelog/2595-from-description b/.github/changelog/2595-from-description
new file mode 100644
index 0000000000..9906da334c
--- /dev/null
+++ b/.github/changelog/2595-from-description
@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Preserve newlines inside pre elements when federating content.