Source

File: wp-admin/includes/class-theme-installer-skin.php

private function do_overwrite() {
		if ( 'upload' !== $this->type || ! is_wp_error( $this->result ) || 'folder_exists' !== $this->result->get_error_code() ) {
			return false;
		}

		$folder = $this->result->get_error_data( 'folder_exists' );
		$folder = rtrim( $folder, '/' );

		$current_theme_data = false;
		$all_themes         = wp_get_themes( array( 'errors' => null ) );

		foreach ( $all_themes as $theme ) {
			$stylesheet_dir = wp_normalize_path( $theme->get_stylesheet_directory() );

			if ( rtrim( $stylesheet_dir, '/' ) !== $folder ) {
				continue;
			}

			$current_theme_data = $theme;
		}

		$new_theme_data = $this->upgrader->new_theme_data;

		if ( ! $current_theme_data || ! $new_theme_data ) {
			return false;
		}

		echo '<h2 class="update-from-upload-heading">' . esc_html( __( 'This theme is already installed.' ) ) . '</h2>';

		// Check errors for current theme.
		if ( is_wp_error( $current_theme_data->errors() ) ) {
			$this->feedback( 'current_theme_has_errors', $current_theme_data->errors()->get_error_message() );
		}

		$this->is_downgrading = version_compare( $current_theme_data['Version'], $new_theme_data['Version'], '>' );

		$is_invalid_parent = false;
		if ( ! empty( $new_theme_data['Template'] ) ) {
			$is_invalid_parent = ! in_array( $new_theme_data['Template'], array_keys( $all_themes ), true );
		}

		$rows = array(
			'Name'        => __( 'Theme name' ),
			'Version'     => __( 'Version' ),
			'Author'      => __( 'Author' ),
			'RequiresWP'  => __( 'Required WordPress version' ),
			'RequiresPHP' => __( 'Required PHP version' ),
			'Template'    => __( 'Parent theme' ),
		);

		$table  = '<table class="update-from-upload-comparison"><tbody>';
		$table .= '<tr><th></th><th>' . esc_html( __( 'Current' ) ) . '</th><th>' . esc_html( __( 'Uploaded' ) ) . '</th></tr>';

		$is_same_theme = true; // Let's consider only these rows.

		foreach ( $rows as $field => $label ) {
			$old_value = $current_theme_data->display( $field, false );
			$old_value = $old_value ? (string) $old_value : '-';

			$new_value = ! empty( $new_theme_data[ $field ] ) ? (string) $new_theme_data[ $field ] : '-';

			if ( $old_value === $new_value && '-' === $new_value && 'Template' === $field ) {
				continue;
			}

			$is_same_theme = $is_same_theme && ( $old_value === $new_value );

			$diff_field     = ( 'Version' !== $field && $new_value !== $old_value );
			$diff_version   = ( 'Version' === $field && $this->is_downgrading );
			$invalid_parent = false;

			if ( 'Template' === $field && $is_invalid_parent ) {
				$invalid_parent = true;
				$new_value     .= ' ' . __( '(not found)' );
			}

			$table .= '<tr><td class="name-label">' . $label . '</td><td>' . wp_strip_all_tags( $old_value ) . '</td>';
			$table .= ( $diff_field || $diff_version || $invalid_parent ) ? '<td class="warning">' : '<td>';
			$table .= wp_strip_all_tags( $new_value ) . '</td></tr>';
		}

		$table .= '</tbody></table>';

		/**
		 * Filters the compare table output for overwriting a theme package on upload.
		 *
		 * @since 5.5.0
		 *
		 * @param string $table              The output table with Name, Version, Author, RequiresWP, and RequiresPHP info.
		 * @param array  $current_theme_data Array with current theme data.
		 * @param array  $new_theme_data     Array with uploaded theme data.
		 */
		echo apply_filters( 'install_theme_overwrite_comparison', $table, $current_theme_data, $new_theme_data );

		$install_actions = array();
		$can_update      = true;

		$blocked_message  = '<p>' . esc_html( __( 'The theme cannot be updated due to the following:' ) ) . '</p>';
		$blocked_message .= '<ul class="ul-disc">';

		$requires_php = isset( $new_theme_data['RequiresPHP'] ) ? $new_theme_data['RequiresPHP'] : null;
		$requires_wp  = isset( $new_theme_data['RequiresWP'] ) ? $new_theme_data['RequiresWP'] : null;

		if ( ! is_php_version_compatible( $requires_php ) ) {
			$error = sprintf(
				/* translators: 1: Current PHP version, 2: Version required by the uploaded theme. */
				__( 'The PHP version on your server is %1$s, however the uploaded theme requires %2$s.' ),
				phpversion(),
				$requires_php
			);

			$blocked_message .= '<li>' . esc_html( $error ) . '</li>';
			$can_update       = false;
		}

		if ( ! is_wp_version_compatible( $requires_wp ) ) {
			$error = sprintf(
				/* translators: 1: Current WordPress version, 2: Version required by the uploaded theme. */
				__( 'Your WordPress version is %1$s, however the uploaded theme requires %2$s.' ),
				get_bloginfo( 'version' ),
				$requires_wp
			);

			$blocked_message .= '<li>' . esc_html( $error ) . '</li>';
			$can_update       = false;
		}

		$blocked_message .= '</ul>';

		if ( $can_update ) {
			if ( $this->is_downgrading ) {
				$warning = sprintf(
					/* translators: %s: Documentation URL. */
					__( 'You are uploading an older version of a current theme. You can continue to install the older version, but be sure to <a href="%s">back up your database and files</a> first.' ),
					__( 'https://wordpress.org/support/article/wordpress-backups/' )
				);
			} else {
				$warning = sprintf(
					/* translators: %s: Documentation URL. */
					__( 'You are updating a theme. Be sure to <a href="%s">back up your database and files</a> first.' ),
					__( 'https://wordpress.org/support/article/wordpress-backups/' )
				);
			}

			echo '<p class="update-from-upload-notice">' . $warning . '</p>';

			$overwrite = $this->is_downgrading ? 'downgrade-theme' : 'update-theme';

			$install_actions['overwrite_theme'] = sprintf(
				'<a class="button button-primary update-from-upload-overwrite" href="%s" target="_parent">%s</a>',
				wp_nonce_url( add_query_arg( 'overwrite', $overwrite, $this->url ), 'theme-upload' ),
				__( 'Replace current with uploaded' )
			);
		} else {
			echo $blocked_message;
		}

		$cancel_url = add_query_arg( 'action', 'upload-theme-cancel-overwrite', $this->url );

		$install_actions['themes_page'] = sprintf(
			'<a class="button" href="%s" target="_parent">%s</a>',
			wp_nonce_url( $cancel_url, 'theme-upload-cancel-overwrite' ),
			__( 'Cancel and go back' )
		);

		/**
		 * Filters the list of action links available following a single theme installation
		 * failure when overwriting is allowed.
		 *
		 * @since 5.5.0
		 *
		 * @param string[] $install_actions Array of theme action links.
		 * @param object   $api             Object containing WordPress.org API theme data.
		 * @param array    $new_theme_data  Array with uploaded theme data.
		 */
		$install_actions = apply_filters( 'install_theme_overwrite_actions', $install_actions, $this->api, $new_theme_data );

		if ( ! empty( $install_actions ) ) {
			printf(
				'<p class="update-from-upload-expired hidden">%s</p>',
				__( 'The uploaded file has expired. Please go back and upload it again.' )
			);
			echo '<p class="update-from-upload-actions">' . implode( ' ', (array) $install_actions ) . '</p>';
		}

		return true;
	}