Fix template part area variation matching (#49500)

* Use a different name for instance and area template part variations to ensure they can all be registered

* Hide area variations in inserter when an instance exists for the same area

packages/block-library/src/template-part/index.php

@@ -173,21 +173,34 @@ function render_block_core_template_part( $attributes ) {
 /**
  * Returns an array of area variation objects for the template part block.
  *
+ * @param array $instance_variations The variations for instances.
+ *
  * @return array Array containing the block variation objects.
  */
-function build_template_part_block_area_variations() {
+function build_template_part_block_area_variations( $instance_variations ) {
 	$variations    = array();
 	$defined_areas = get_allowed_block_template_part_areas();
+
 	foreach ( $defined_areas as $area ) {
 		if ( 'uncategorized' !== $area['area'] ) {
+			$has_instance_for_area = false;
+			foreach ( $instance_variations as $variation ) {
+				if ( $variation['attributes']['area'] === $area['area'] ) {
+					$has_instance_for_area = true;
+					break;
+				}
+			}
+
+			$scope = $has_instance_for_area ? array() : array( 'inserter' );
+
 			$variations[] = array(
-				'name'        => $area['area'],
+				'name'        => 'area_' . $area['area'],
 				'title'       => $area['label'],
 				'description' => $area['description'],
 				'attributes'  => array(
 					'area' => $area['area'],
 				),
-				'scope'       => array( 'inserter' ),
+				'scope'       => $scope,
 				'icon'        => $area['icon'],
 			);
 		}
@@ -223,7 +236,7 @@ function build_template_part_block_instance_variations() {
 
 	foreach ( $template_parts as $template_part ) {
 		$variations[] = array(
-			'name'        => sanitize_title( $template_part->slug ),
+			'name'        => 'instance_' . sanitize_title( $template_part->slug ),
 			'title'       => $template_part->title,
 			// If there's no description for the template part don't show the
 			// block description. This is a bit hacky, but prevent the fallback
@@ -255,7 +268,9 @@ function build_template_part_block_instance_variations() {
  * @return array Array containing the block variation objects.
  */
 function build_template_part_block_variations() {
-	return array_merge( build_template_part_block_area_variations(), build_template_part_block_instance_variations() );
+	$instance_variations = build_template_part_block_instance_variations();
+	$area_variations     = build_template_part_block_area_variations( $instance_variations );
+	return array_merge( $area_variations, $instance_variations );
 }
 
 /**