Fix flash when clicking on template name when a plugin registered template matches a default WP theme template

src/wp-includes/block-template-utils.php

@@ -1168,9 +1168,35 @@ function get_block_templates( $query = array(), $template_type = 'wp_template' )
 		 * over the theme-provided ones, so we skip querying and building them.
 		 */
 		$query['slug__not_in'] = wp_list_pluck( $query_result, 'slug' );
-		$template_files        = _get_block_templates_files( $template_type, $query );
+		/*
+		 * We need to unset the post_type query param because some templates
+		 * would be excluded otherwise, like `page.html` when looking for
+		 * `page` templates. We need all templates so we can exclude duplicates
+		 * from plugin-registered templates.
+		 * See: https://github.com/WordPress/gutenberg/issues/65584
+		 */
+		$template_files_query = $query;
+		unset( $template_files_query['post_type'] );
+		$template_files = _get_block_templates_files( $template_type, $template_files_query );
 		foreach ( $template_files as $template_file ) {
-			$query_result[] = _build_block_template_result_from_file( $template_file, $template_type );
+			// If the query doesn't specify a post type, or it does and the template matches the post type, add it.
+			if (
+				! isset( $query['post_type'] ) ||
+				(
+					isset( $template_file['postTypes'] ) &&
+					in_array( $query['post_type'], $template_file['postTypes'], true )
+				)
+			) {
+				$query_result[] = _build_block_template_result_from_file( $template_file, $template_type );
+			} elseif ( ! isset( $template_file['postTypes'] ) ) {
+				// The custom templates with no associated post types are available for all post types as long
+				// as they are not default templates.
+				$candidate              = _build_block_template_result_from_file( $template_file, $template_type );
+				$default_template_types = get_default_block_template_types();
+				if ( ! isset( $default_template_types[ $candidate->slug ] ) ) {
+					$query_result[] = $candidate;
+				}
+			}
 		}
 
 		if ( 'wp_template' === $template_type ) {

tests/phpunit/tests/blocks/getBlockTemplates.php

@@ -228,4 +228,64 @@
 			),
 		);
 	}
+
+	/**
+	 * @dataProvider data_get_block_templates_should_not_leak_plugin_registered_templates_with_default_post_type_slugs
+	 * @ticket 62319
+
+	 @covers ::get_block_templates
+	 *
+	 * @param string $template_slug Default slug for the post type.
+	 * @param string $post_type     Post type for query.
+	 * @param array  $expected      Expected template IDs.
+	 */
+	public function test_get_block_templates_should_not_leak_plugin_registered_templates_with_default_post_type_slugs( $template_slug, $post_type, $expected ) {
+		$template_name = 'test-plugin//' . $template_slug;
+		$template_args = array(
+			'content'     => 'Template content',
+			'title'       => 'Test Template for ' . $post_type,
+			'description' => 'Description of test template',
+			'post_types'  => array( $post_type ),
+		);
+		register_block_template( $template_name, $template_args );
+
+		$templates = get_block_templates( array( 'post_type' => $post_type ) );
+
+		$this->assertSameSets(
+			$expected,
+			$this->get_template_ids( $templates )
+		);
+
+		unregister_block_template( $template_name );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * Make sure that plugin-registered templates with default post type slugs (ie: `single` or `page`)
+	 * don't leak into `get_block_templates()`.
+	 * See: https://core.trac.wordpress.org/ticket/62319.
+	 *
+	 * @return array
+	 */
+	public function data_get_block_templates_should_not_leak_plugin_registered_templates_with_default_post_type_slugs() {
+		return array(
+			'post' => array(
+				'template_slug' => 'single',
+				'post_type'     => 'post',
+				'expected'      => array(
+					'block-theme//custom-hero-template',
+					'block-theme//custom-single-post-template',
+				),
+			),
+			'page' => array(
+				'template_slug' => 'page',
+				'post_type'     => 'page',
+				'expected'      => array(
+					'block-theme//custom-hero-template',
+					'block-theme//page-home',
+				),
+			),
+		);
+	}
 }