Fix bug when comparing options that have a pre filter.

src/wp-includes/option.php

@@ -776,6 +776,24 @@ function update_option( $option, $value, $autoload = null ) {
 	 */
 	$value = apply_filters( 'pre_update_option', $value, $option, $old_value );
 
+	/*
+	 * To get the actual raw old value from the database, any existing pre filters need to be temporarily disabled.
+	 * Immediately after getting the raw value, they are reinstated.
+	 * The raw value is only used to determine whether a value is present in the database. It is not used anywhere
+	 * else, and is not passed to any of the hooks either.
+	 */
+	if ( has_filter( "pre_option_{$option}" ) ) {
+		global $wp_filter;
+
+		$old_filters = $wp_filter[ "pre_option_{$option}" ];
+		unset( $wp_filter[ "pre_option_{$option}" ] );
+
+		$raw_old_value                       = get_option( $option );
+		$wp_filter[ "pre_option_{$option}" ] = $old_filters;
+	} else {
+		$raw_old_value = $old_value;
+	}
+
 	/** This filter is documented in wp-includes/option.php */
 	$default_value = apply_filters( "default_option_{$option}", false, $option, false );
 
@@ -787,11 +805,11 @@ function update_option( $option, $value, $autoload = null ) {
 	 *
 	 * See https://core.trac.wordpress.org/ticket/38903 and https://core.trac.wordpress.org/ticket/22192.
 	 */
-	if ( $old_value !== $default_value && _is_equal_database_value( $old_value, $value ) ) {
+	if ( $raw_old_value !== $default_value && _is_equal_database_value( $raw_old_value, $value ) ) {
 		return false;
 	}
 
-	if ( $old_value === $default_value ) {
+	if ( $raw_old_value === $default_value ) {
 
 		// Default setting for new options is 'yes'.
 		if ( null === $autoload ) {

tests/phpunit/tests/option/option.php

@@ -439,7 +439,6 @@ public function test_update_loosey_options_from_refreshed_cache( $old_value, $ne
 		}
 	}
 
-
 	/**
 	 * Data provider.
 	 *
@@ -581,4 +580,58 @@ static function () use ( $default_value ) {
 
 		$this->assertSame( 1, $actual );
 	}
+
+	/**
+	 * Tests that a non-existing option is added even when its pre filter returns a value.
+	 *
+	 * @ticket 22192
+	 *
+	 * @covers ::update_option
+	 */
+	public function test_update_option_with_pre_filter_adds_missing_option() {
+		// Force a return value of integer 0.
+		add_filter( 'pre_option_foo', '__return_zero' );
+
+		/*
+		 * This should succeed, since the 'foo' option does not exist in the database.
+		 * The default value is false, so it differs from 0.
+		 */
+		$this->assertTrue( update_option( 'foo', 0 ) );
+	}
+
+	/**
+	 * Tests that an existing option is updated even when its pre filter returns the same value.
+	 *
+	 * @ticket 22192
+	 *
+	 * @covers ::update_option
+	 */
+	public function test_update_option_with_pre_filter_updates_option_with_different_value() {
+		// Add the option with a value of 1 to the database.
+		add_option( 'foo', 1 );
+
+		// Force a return value of integer 0.
+		add_filter( 'pre_option_foo', '__return_zero' );
+
+		/*
+		 * This should succeed, since the 'foo' option has a value of 1 in the database.
+		 * Therefore it differs from 0 and should be updated.
+		 */
+		$this->assertTrue( update_option( 'foo', 0 ) );
+	}
+
+	/**
+	 * Tests that calling update_option() does not permanently remove pre filters.
+	 *
+	 * @ticket 22192
+	 *
+	 * @covers ::update_option
+	 */
+	public function test_update_option_maintains_pre_filters() {
+		add_filter( 'pre_option_foo', '__return_zero' );
+		update_option( 'foo', 0 );
+
+		// Assert that the filter is still present.
+		$this->assertSame( 10, has_filter( 'pre_option_foo', '__return_zero' ) );
+	}
 }