Code Quality: Resolve the isset.variable PHPStan errors

phpstan.neon.dist

@@ -57,7 +57,6 @@ includes:
 	- tests/phpstan/baselines/instanceof.alwaysTrue.neon
 	- tests/phpstan/baselines/isset.offset.neon
 	- tests/phpstan/baselines/isset.property.neon
-	- tests/phpstan/baselines/isset.variable.neon
 	- tests/phpstan/baselines/method.childParameterType.neon
 	- tests/phpstan/baselines/method.nonObject.neon
 	- tests/phpstan/baselines/method.notFound.neon

src/wp-admin/includes/class-custom-image-header.php

@@ -841,7 +841,7 @@ public function step_2() {
 			$file          = get_attached_file( $attachment_id, true );
 			$url           = wp_get_attachment_image_src( $attachment_id, 'full' );
 			$url           = $url[0];
-		} elseif ( isset( $_POST ) ) {
+		} else {
 			$data          = $this->step_2_manage_upload();
 			$attachment_id = $data['attachment_id'];
 			$file          = $data['file'];

src/wp-admin/includes/file.php

@@ -397,9 +397,10 @@ function wp_edit_theme_plugin_file( $args ) {
 	$file    = $args['file'];
 	$content = $args['newcontent'];
 
-	$plugin    = null;
-	$theme     = null;
-	$real_file = null;
+	$plugin     = null;
+	$stylesheet = null;
+	$theme      = null;
+	$real_file  = null;
 
 	if ( ! empty( $args['plugin'] ) ) {
 		$plugin = $args['plugin'];
@@ -560,7 +561,7 @@ function wp_edit_theme_plugin_file( $args ) {
 		// Attempt loopback request to editor to see if user just whitescreened themselves.
 		if ( $plugin ) {
 			$url = add_query_arg( compact( 'plugin', 'file' ), admin_url( 'plugin-editor.php' ) );
-		} elseif ( isset( $stylesheet ) ) {
+		} elseif ( $stylesheet ) {
 			$url = add_query_arg(
 				array(
 					'theme' => $stylesheet,

src/wp-admin/includes/media.php

@@ -1773,7 +1773,7 @@ function get_media_item( $attachment_id, $args = null ) {
 
 	if ( isset( $_GET['post_id'] ) ) {
 		$calling_post_id = absint( $_GET['post_id'] );
-	} elseif ( isset( $_POST ) && count( $_POST ) ) {// Like for async-upload where $_GET['post_id'] isn't set.
+	} elseif ( ! empty( $_POST ) ) {// Like for async-upload where $_GET['post_id'] isn't set.
 		$calling_post_id = $post->post_parent;
 	}
 

src/wp-includes/class-wp-block-parser.php

@@ -268,7 +268,7 @@ public function next_token() {
 		$is_closer = isset( $matches['closer'] ) && -1 !== $matches['closer'][1];
 		$is_void   = isset( $matches['void'] ) && -1 !== $matches['void'][1];
 		$namespace = $matches['namespace'];
-		$namespace = ( isset( $namespace ) && -1 !== $namespace[1] ) ? $namespace[0] : 'core/';
+		$namespace = -1 !== $namespace[1] ? $namespace[0] : 'core/';
 		$name      = $namespace . $matches['name'][0];
 		$has_attrs = isset( $matches['attrs'] ) && -1 !== $matches['attrs'][1];
 

src/wp-includes/class-wp-oembed.php

@@ -674,6 +674,7 @@ private function _parse_xml( $response_body ) {
 			return false;
 		}
 
+		$loader = null;
 		if ( PHP_VERSION_ID < 80000 ) {
 			/*
 			 * This function has been deprecated in PHP 8.0 because in libxml 2.9.0, external entity loading
@@ -688,7 +689,7 @@ private function _parse_xml( $response_body ) {
 
 		libxml_use_internal_errors( $errors );
 
-		if ( PHP_VERSION_ID < 80000 && isset( $loader ) ) {
+		if ( PHP_VERSION_ID < 80000 ) {
 			// phpcs:ignore PHPCompatibility.FunctionUse.RemovedFunctions.libxml_disable_entity_loaderDeprecated
 			libxml_disable_entity_loader( $loader );
 		}

src/wp-includes/template.php

@@ -782,7 +782,9 @@ function locate_template( $template_names, $load = false, $load_once = true, $ar
 function load_template( $_template_file, $load_once = true, $args = array() ) {
 	global $posts, $post, $wp_did_header, $wp_query, $wp_rewrite, $wpdb, $wp_version, $wp, $id, $comment, $user_ID;
 
-	if ( is_array( $wp_query->query_vars ) ) {
+	/** @var array{ s?: scalar, ... } $query_vars */
+	$query_vars = $wp_query->query_vars;
+	if ( is_array( $query_vars ) ) {
 		/*
 		 * This use of extract() cannot be removed. There are many possible ways that
 		 * templates could depend on variables that it creates existing, and no way to
@@ -792,11 +794,11 @@ function load_template( $_template_file, $load_once = true, $args = array() ) {
 		 * function variables cannot be overwritten.
 		 */
 		// phpcs:ignore WordPress.PHP.DontExtract.extract_extract
-		extract( $wp_query->query_vars, EXTR_SKIP );
+		extract( $query_vars, EXTR_SKIP );
 	}
 
 	if ( isset( $s ) ) {
-		$s = esc_attr( $s ); // @phpstan-ignore variable.undefined (It's extracted from query vars.)
+		$s = esc_attr( (string) $s );
 	}
 
 	/**