HTML API: Guard against non-string attribute values.

lib/experimental/interactivity-api/directive-processing.php

@@ -136,11 +136,11 @@ function gutenberg_interactivity_evaluate_reference( $path, array $context = arr
 	);
 
 	/*
-	 * Check first if the directive path is preceded by a negator operator (!),
+	 * Check first if the directive path is preceded by a negation operator (!),
 	 * indicating that the value obtained from the Interactivity Store (or the
 	 * passed context) using the subsequent path should be negated.
 	 */
-	$should_negate_value = '!' === $path[0];
+	$should_negate_value = strlen( $path ) > 0 && '!' === $path[0];
 
 	$path          = $should_negate_value ? substr( $path, 1 ) : $path;
 	$path_segments = explode( '.', $path );

lib/experimental/interactivity-api/directives/wp-bind.php

@@ -26,6 +26,7 @@ function gutenberg_interactivity_process_wp_bind( $tags, $context ) {
 		}
 
 		$expr  = $tags->get_attribute( $attr );
+		$expr  = is_string( $expr ) ? $expr : '';
 		$value = gutenberg_interactivity_evaluate_reference( $expr, $context->get_context() );
 		$tags->set_attribute( $bound_attr, $value );
 	}

lib/experimental/interactivity-api/directives/wp-class.php

@@ -26,6 +26,7 @@ function gutenberg_interactivity_process_wp_class( $tags, $context ) {
 		}
 
 		$expr      = $tags->get_attribute( $attr );
+		$expr      = is_string( $expr ) ? $expr : '';
 		$add_class = gutenberg_interactivity_evaluate_reference( $expr, $context->get_context() );
 		if ( $add_class ) {
 			$tags->add_class( $class_name );

lib/experimental/interactivity-api/directives/wp-context.php

@@ -18,7 +18,7 @@ function gutenberg_interactivity_process_wp_context( $tags, $context ) {
 	}
 
 	$value = $tags->get_attribute( 'data-wp-context' );
-	if ( null === $value ) {
+	if ( ! is_string( $value ) || empty( $value ) ) {
 		// No data-wp-context directive.
 		return;
 	}

lib/experimental/interactivity-api/directives/wp-style.php

@@ -26,9 +26,11 @@ function gutenberg_interactivity_process_wp_style( $tags, $context ) {
 		}
 
 		$expr        = $tags->get_attribute( $attr );
+		$expr        = is_string( $expr ) ? $expr : '';
 		$style_value = gutenberg_interactivity_evaluate_reference( $expr, $context->get_context() );
 		if ( $style_value ) {
 			$style_attr = $tags->get_attribute( 'style' );
+			$style_attr = is_string( $style_value ) ? $style_attr : '';
 			$style_attr = gutenberg_interactivity_set_style( $style_attr, $style_name, $style_value );
 			$tags->set_attribute( 'style', $style_attr );
 		} else {

lib/experimental/interactivity-api/directives/wp-text.php

@@ -18,7 +18,7 @@ function gutenberg_interactivity_process_wp_text( $tags, $context ) {
 	}
 
 	$value = $tags->get_attribute( 'data-wp-text' );
-	if ( null === $value ) {
+	if ( ! is_string( $value ) || empty( $value ) ) {
 		return;
 	}
 

packages/block-library/src/cover/index.php

@@ -54,6 +54,7 @@ function render_block_core_cover( $attributes, $content ) {
 		$processor->next_tag();
 
 		$styles         = $processor->get_attribute( 'style' );
+		$styles         = is_string( $styles ) ? $styles : '';
 		$merged_styles  = ! empty( $styles ) ? $styles . ';' : '';
 		$merged_styles .= 'background-image:url(' . esc_url( $current_featured_image ) . ');';