Ticket #9757: 9757.5.patch

src/wp-admin/css/themes.css

@@ -1029 +1029 @@
         overflow: hidden;
         position: relative;
         top: 10px;
-}
-
-.upload-plugin-wrap {
-        display: none;
+        text-align: center;
 }
 
 .show-upload-view .upload-theme,
@@ -1048 +1045 @@
         border: 1px solid #ccd0d4;
         padding: 30px;
         margin: 30px auto;
-        max-width: 380px;
-        display: flex;
+        display: inline-flex;
         justify-content: space-between;
         align-items: center;
 }
 
+.upload-theme .wp-upload-form input[type="file"],
+.upload-plugin .wp-upload-form input[type="file"] {
+        margin-right: 10px;
+}
+
 .upload-theme .install-help,
 .upload-plugin .install-help {
         color: #555d66; /* #f1f1f1 background */
@@ -1092 +1093 @@
         .upload-theme .install-help {
                 font-size: 15px;
                 padding: 20px 0 0;
-                text-align: left;
         }
 }
 
@@ -1115 +1115 @@
         line-height: 1.9;
 }
 
+.compare-themes-table,
+.compare-plugins-table {
+        text-align: left;
+        margin: 1em 0 2em;
+        border-collapse: collapse;
+}
+
+.compare-themes-table th,
+.compare-plugins-table th {
+        font-weight: bold;
+        padding: 3px 10px;
+}
+
+.compare-themes-table td,
+.compare-plugins-table td {
+        padding: 3px 10px;
+}
+
+.compare-themes-table tr.warning,
+.compare-plugins-table tr.warning,
+a.ovewrite-uploaded-theme {
+        color: #a00;
+}
+
+a.ovewrite-uploaded-plugin {
+        color: #a00;
+        margin-left: 10px;
+}
+
+
+a.ovewrite-uploaded-theme:hover,
+a.ovewrite-uploaded-plugin:hover {
+        color: #d80707;
+}
+
 /*------------------------------------------------------------------------------
   16.3 - Custom Header Screen
 ------------------------------------------------------------------------------*/

src/wp-admin/includes/class-plugin-installer-skin.php

@@ -18 +18 @@
 class Plugin_Installer_Skin extends WP_Upgrader_Skin {
         public $api;
         public $type;
+        public $url;
+        public $overwrite;
+
+        private $is_downgrading = false;
 
         /**
          * @param array $args
          */
         public function __construct( $args = array() ) {
                 $defaults = array(
-                        'type'   => 'web',
-                        'url'    => '',
-                        'plugin' => '',
-                        'nonce'  => '',
-                        'title'  => '',
+                        'type'      => 'web',
+                        'url'       => '',
+                        'plugin'    => '',
+                        'nonce'     => '',
+                        'title'     => '',
+                        'overwrite' => '',
                 );
                 $args     = wp_parse_args( $args, $defaults );
 
-                $this->type = $args['type'];
-                $this->api  = isset( $args['api'] ) ? $args['api'] : array();
+                $this->type      = $args['type'];
+                $this->url       = $args['url'];
+                $this->api       = isset( $args['api'] ) ? $args['api'] : array();
+                $this->overwrite = $args['overwrite'];
 
                 parent::__construct( $args );
         }
@@ -43 +50 @@
         public function before() {
                 if ( ! empty( $this->api ) ) {
                         $this->upgrader->strings['process_success'] = sprintf(
-                                /* translators: 1: Plugin name, 2: Plugin version. */
-                                __( 'Successfully installed the plugin <strong>%1$s %2$s</strong>.' ),
+                                $this->upgrader->strings['process_success_specific'],
                                 $this->api->name,
                                 $this->api->version
                         );
@@ -54 +60 @@
         /**
          */
         public function after() {
+                // Check if the plugin can be overwritten and output the HTML.
+                if ( $this->do_overwrite() ) {
+                        return;
+                }
+
                 $plugin_file = $this->upgrader->plugin_info();
 
                 $install_actions = array();
@@ -117 +128 @@
 
                 if ( ! $this->result || is_wp_error( $this->result ) ) {
                         unset( $install_actions['activate_plugin'], $install_actions['network_activate'] );
-                } elseif ( ! current_user_can( 'activate_plugin', $plugin_file ) ) {
+                } elseif ( ! current_user_can( 'activate_plugin', $plugin_file ) || is_plugin_active( $plugin_file ) ) {
                         unset( $install_actions['activate_plugin'] );
                 }
 
@@ -138 +149 @@
                         $this->feedback( implode( ' ', (array) $install_actions ) );
                 }
         }
+
+        /**
+         * Check if the plugin can be overwritten and output the HTML for overwriting a plugin on upload.
+         *
+         * @since 5.5.0
+         *
+         * @return bool Whether the plugin can be overwritten and HTML was outputted.
+         */
+        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 = ltrim( substr( $folder, strlen( WP_PLUGIN_DIR ) ), '/' );
+
+                $current_plugin_data = false;
+                foreach ( get_plugins() as $plugin => $plugin_data ) {
+                        if ( strrpos( $plugin, $folder ) !== 0 ) {
+                                continue;
+                        }
+
+                        $current_plugin_data = $plugin_data;
+                }
+
+                if ( empty( $current_plugin_data ) || empty( $this->upgrader->new_plugin_data ) ) {
+                        return false;
+                }
+
+                $this->feedback( 'compare_before_overwrite' );
+
+                $this->is_downgrading = version_compare( $current_plugin_data['Version'], $this->upgrader->new_plugin_data['Version'], '>' );
+
+                $rows = array(
+                        'Name'        => __( 'Plugin Name' ),
+                        'Version'     => __( 'Version' ),
+                        'Author'      => __( 'Author' ),
+                        'RequiresWP'  => __( 'Required WordPress version' ),
+                        'RequiresPHP' => __( 'Required PHP version' ),
+                );
+
+                $table  = '<table class="compare-plugins-table"><tbody>';
+                $table .= '<tr><th></th><th>' . esc_html( __( 'Current' ) ) . '</th><th>' . esc_html( __( 'Uploaded' ) ) . '</th></tr>';
+
+                $is_same_plugin = true; // Let's consider only these rows
+                foreach ( $rows as $field => $label ) {
+                        $old_value = ! empty( $current_plugin_data[ $field ] ) ? $current_plugin_data[ $field ] : '-';
+                        $new_value = ! empty( $this->upgrader->new_plugin_data[ $field ] ) ? $this->upgrader->new_plugin_data[ $field ] : '-';
+
+                        $is_same_plugin = $is_same_plugin && ( $old_value === $new_value );
+
+                        $diff_field   = ( 'Version' !== $field && $new_value !== $old_value );
+                        $diff_version = ( 'Version' === $field && $this->is_downgrading );
+
+                        $table .= ( $diff_field || $diff_version ) ? '<tr class="warning">' : '<tr>';
+                        $table .= '<td>' . $label . '</td><td>' . esc_html( $old_value ) . '</td><td>' . esc_html( $new_value ) . '</td></tr>';
+                }
+
+                $table .= '</tbody></table>';
+
+                if ( $is_same_plugin ) {
+                        $this->feedback( 'reuploading_plugin' );
+                }
+
+                /**
+                 * Filters the compare table output for overwrite a plugin package on upload.
+                 *
+                 * @since 5.5.0
+                 *
+                 * @param string   $table                The output table with Name, Version, Author, RequiresWP and RequiresPHP info.
+                 * @param array    $current_plugin_data  Array with current plugin data.
+                 * @param array    $new_plugin_data      Array with uploaded plugin data.
+                 */
+                echo apply_filters( 'install_plugin_ovewrite_comparison', $table, $current_plugin_data, $this->upgrader->new_plugin_data );
+
+                // Action links.
+                $install_actions = array(
+                        'plugins_page' => sprintf(
+                                '<a href="%s">%s</a>',
+                                self_admin_url( 'plugin-install.php' ),
+                                __( 'Cancel and go back' )
+                        ),
+                );
+
+                $can_update = true;
+
+                if ( ! empty( $this->upgrader->new_plugin_data['RequiresPHP'] ) && version_compare( phpversion(), $this->upgrader->new_plugin_data['RequiresPHP'], '<' ) ) {
+                        $error = sprintf(
+                                /* translators: 1: Current PHP version, 2: Version required by the uploaded plugin. */
+                                __( 'The plugin cannot be updated. The PHP version on your server is %1$s, however the uploaded plugin requires %2$s.' ),
+                                phpversion(),
+                                $this->upgrader->new_plugin_data['RequiresPHP']
+                        );
+
+                        $this->feedback( '<div class="notice notice-error inline"><p>' . esc_html( $error ) . '</p></div>' );
+                        $can_update = false;
+                }
+
+                if ( ! empty( $this->upgrader->new_plugin_data['RequiresWP'] ) && version_compare( $GLOBALS['wp_version'], $this->upgrader->new_plugin_data['RequiresWP'], '<' ) ) {
+                        $error = sprintf(
+                                /* translators: 1: Current WordPress version, 2: Version required by the uploaded plugin. */
+                                __( 'The plugin cannot be updated. Your WordPress version is %1$s, however the uploaded plugin requires %2$s.' ),
+                                $GLOBALS['wp_version'],
+                                $this->upgrader->new_plugin_data['RequiresWP']
+                        );
+
+                        $this->feedback( '<div class="notice notice-error inline"><p>' . esc_html( $error ) . '</p></div>' );
+                        $can_update = false;
+                }
+
+                if ( $can_update ) {
+                        $warning = __( '<strong>Important:</strong> Before updating, please <a href="https://wordpress.org/support/article/wordpress-backups/">back up your database and files</a>.' );
+                        $this->feedback( '<div class="notice notice-warning inline"><p>' . $warning . '</p></div>' );
+
+                        $overwrite = 'update-plugin';
+                        $label     = __( 'Remove current and install the uploaded version' );
+
+                        if ( $this->is_downgrading ) {
+                                $overwrite = 'downgrade-plugin';
+
+                                if ( isset( $this->upgrader->new_plugin_data['Version'] ) ) {
+                                        $label = sprintf( __( 'Remove current and install version %s' ), $this->upgrader->new_plugin_data['Version'] );
+                                }
+                        }
+
+                        $install_actions['ovewrite_plugin'] = sprintf(
+                                '<a class="ovewrite-uploaded-plugin" href="%s" target="_parent">%s</a>',
+                                wp_nonce_url( add_query_arg( 'overwrite', $overwrite, $this->url ), 'plugin-upload' ),
+                                esc_html( $label )
+                        );
+                }
+
+                /**
+                 * Filters the list of action links available following a single plugin installation failed but ovewrite is allowed.
+                 *
+                 * @since 5.5.0
+                 *
+                 * @param string[] $install_actions Array of plugin action links.
+                 * @param object   $api             Object containing WordPress.org API plugin data.
+                 * @param array    $new_plugin_data Array with uploaded plugin data.
+                 */
+                $install_actions = apply_filters( 'install_plugin_ovewrite_actions', $install_actions, $this->api, $this->upgrader->new_plugin_data );
+
+                if ( ! empty( $install_actions ) ) {
+                        $this->feedback( implode( ' ', (array) $install_actions ) );
+                }
+
+                return true;
+        }
 }

src/wp-admin/includes/class-plugin-upgrader.php

@@ -38 +38 @@
          */
         public $bulk = false;
 
+        /**
+         * New plugin info.
+         *
+         * @since 5.5.0
+         * @var array $new_plugin_data
+         *
+         * @see check_package()
+         */
+        public $new_plugin_data = [];
+
         /**
          * Initialize the upgrade strings.
          *
@@ -54 +64 @@
                 $this->strings['process_failed']       = __( 'Plugin update failed.' );
                 $this->strings['process_success']      = __( 'Plugin updated successfully.' );
                 $this->strings['process_bulk_success'] = __( 'Plugins updated successfully.' );
+
+                /* translators: 1: Plugin name, 2: Plugin version. */
+                $this->strings['process_success_specific'] = __( 'Successfully installed the plugin <strong>%1$s %2$s</strong>.' );
         }
 
         /**
@@ -67 +80 @@
                 $this->strings['downloading_package'] = sprintf( __( 'Downloading installation package from %s&#8230;' ), '<span class="code">%s</span>' );
                 $this->strings['unpack_package']      = __( 'Unpacking the package&#8230;' );
                 $this->strings['installing_package']  = __( 'Installing the plugin&#8230;' );
+                $this->strings['remove_old']          = __( 'Removing the current plugin&#8230;' );
+                $this->strings['remove_old_failed']   = __( 'Could not remove the current plugin.' );
                 $this->strings['no_files']            = __( 'The plugin contains no files.' );
                 $this->strings['process_failed']      = __( 'Plugin installation failed.' );
                 $this->strings['process_success']     = __( 'Plugin installed successfully.' );
+
+                $this->strings['reuploading_plugin']       = __( 'Seems you have uploaded a plugin that is already installed.' );
+                $this->strings['compare_before_overwrite'] = __( 'Plugin information:' );
+
+                if ( 'update-plugin' === $this->skin->overwrite ) {
+                        $this->strings['installing_package'] = __( 'Updating the plugin&#8230;' );
+                        $this->strings['process_failed']     = __( 'Plugin update failed.' );
+                        $this->strings['process_success']    = __( 'Plugin updated successfully.' );
+                }
+
+                if ( 'downgrade-plugin' === $this->skin->overwrite ) {
+                        $this->strings['installing_package'] = __( 'Downgrading the plugin&#8230;' );
+                        $this->strings['process_failed']     = __( 'Plugin downgrade failed.' );
+                        $this->strings['process_success']    = __( 'Plugin downgraded successfully.' );
+                }
         }
 
         /**
@@ -88 +118 @@
          * @return bool|WP_Error True if the installation was successful, false or a WP_Error otherwise.
          */
         public function install( $package, $args = array() ) {
-
                 $defaults    = array(
                         'clear_update_cache' => true,
+                        'overwrite_package'  => false, // Do not overwrite files.
                 );
                 $parsed_args = wp_parse_args( $args, $defaults );
 
@@ -107 +137 @@
                         array(
                                 'package'           => $package,
                                 'destination'       => WP_PLUGIN_DIR,
-                                'clear_destination' => false, // Do not overwrite files.
+                                'clear_destination' => $args['overwrite_package'],
                                 'clear_working'     => true,
                                 'hook_extra'        => array(
                                         'type'   => 'plugin',
@@ -126 +156 @@
                 // Force refresh of plugin update information.
                 wp_clean_plugins_cache( $parsed_args['clear_update_cache'] );
 
+                if ( $parsed_args['overwrite_package'] ) {
+                        /**
+                         * Fires when the upgrader process a install forcing a package overwrite.
+                         *
+                         * @since 5.5.0
+                         *
+                         * @param string  $package          The package file.
+                         * @param array   $new_plugin_data  The new plugin data.
+                         * @param string  $package_type     The package type (plugin or theme).
+                         */
+                        do_action( 'upgrader_overwrited_package', $package, $this->new_plugin_data, 'plugin' );
+                }
+
                 return true;
         }
 
@@ -145 +188 @@
          * @return bool|WP_Error True if the upgrade was successful, false or a WP_Error object otherwise.
          */
         public function upgrade( $plugin, $args = array() ) {
-
                 $defaults    = array(
                         'clear_update_cache' => true,
                 );
@@ -223 +265 @@
          * @return array|false An array of results indexed by plugin file, or false if unable to connect to the filesystem.
          */
         public function bulk_upgrade( $plugins, $args = array() ) {
-
                 $defaults    = array(
                         'clear_update_cache' => true,
                 );
@@ -349 +390 @@
         public function check_package( $source ) {
                 global $wp_filesystem;
 
+                $this->new_plugin_data = [];
+
                 if ( is_wp_error( $source ) ) {
                         return $source;
                 }
@@ -359 +402 @@
                 }
 
                 // Check that the folder contains at least 1 valid plugin.
-                $plugins_found = false;
-                $files         = glob( $working_directory . '*.php' );
+                $files = glob( $working_directory . '*.php' );
                 if ( $files ) {
                         foreach ( $files as $file ) {
                                 $info = get_plugin_data( $file, false, false );
                                 if ( ! empty( $info['Name'] ) ) {
-                                        $plugins_found = true;
+                                        $this->new_plugin_data = $info;
                                         break;
                                 }
                         }
                 }
 
-                if ( ! $plugins_found ) {
+                if ( empty( $this->new_plugin_data ) ) {
                         return new WP_Error( 'incompatible_archive_no_plugins', $this->strings['incompatible_archive'], __( 'No valid plugins were found.' ) );
                 }
 
+                if ( ! empty( $this->new_plugin_data['RequiresPHP'] ) && version_compare( phpversion(), $this->new_plugin_data['RequiresPHP'], '<' ) ) {
+            return new WP_Error( 'incompatible_php_required_version', $this->strings['incompatible_archive'], __( 'Current PHP version does not meet minimum requirements for this plugin.' ) );
+        }
+
                 return $source;
         }
 

src/wp-admin/includes/class-theme-installer-skin.php

@@ -18 +18 @@
 class Theme_Installer_Skin extends WP_Upgrader_Skin {
         public $api;
         public $type;
+        public $url;
+        public $overwrite;
+
+        private $is_downgrading = false;
 
         /**
          * @param array $args
          */
         public function __construct( $args = array() ) {
                 $defaults = array(
-                        'type'  => 'web',
-                        'url'   => '',
-                        'theme' => '',
-                        'nonce' => '',
-                        'title' => '',
+                        'type'      => 'web',
+                        'url'       => '',
+                        'theme'     => '',
+                        'nonce'     => '',
+                        'title'     => '',
+                        'overwrite' => '',
                 );
                 $args     = wp_parse_args( $args, $defaults );
 
-                $this->type = $args['type'];
-                $this->api  = isset( $args['api'] ) ? $args['api'] : array();
+                $this->type      = $args['type'];
+                $this->url       = $args['url'];
+                $this->api       = isset( $args['api'] ) ? $args['api'] : array();
+                $this->overwrite = $args['overwrite'];
 
                 parent::__construct( $args );
         }
@@ -53 +60 @@
         /**
          */
         public function after() {
+                if ( $this->do_overwrite() ) {
+                        return;
+                }
+
                 if ( empty( $this->upgrader->result['destination_name'] ) ) {
                         return;
                 }
@@ -130 +141 @@
 
                 if ( ! $this->result || is_wp_error( $this->result ) || is_network_admin() || ! current_user_can( 'switch_themes' ) ) {
                         unset( $install_actions['activate'], $install_actions['preview'] );
+                } elseif ( get_option( 'template' ) === $stylesheet ) {
+                        unset( $install_actions['activate'] );
                 }
 
                 /**
@@ -147 +160 @@
                         $this->feedback( implode( ' | ', (array) $install_actions ) );
                 }
         }
+
+        /**
+         * Check if the theme can be overwritten and output the HTML for overwriting a theme on upload.
+         *
+         * @since 5.5.0
+         *
+         * @return bool Whether the theme can be overwritten and HTML was outputted.
+         */
+        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 ) {
+                        if ( rtrim( $theme->get_stylesheet_directory(), '/' ) !== $folder ) {
+                                continue;
+                        }
+
+                        $current_theme_data = $theme;
+                }
+
+                if ( empty( $current_theme_data ) || empty( $this->upgrader->new_theme_data ) ) {
+                        return false;
+                }
+
+                $this->is_downgrading = version_compare( $current_theme_data['Version'], $this->upgrader->new_theme_data['Version'], '>' );
+
+                $is_invalid_parent = false;
+                if ( ! empty( $this->upgrader->new_theme_data['Template'] ) ) {
+                        $is_invalid_parent = ! in_array( $this->upgrader->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="compare-themes-table"><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 ? $old_value : '-';
+
+                        $new_value = ! empty( $this->upgrader->new_theme_data[ $field ] ) ? $this->upgrader->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 .= ( $diff_field || $diff_version || $invalid_parent ) ? '<tr class="warning">' : '<tr>';
+                        $table .= '<td>' . $label . '</td><td>' . esc_html( $old_value ) . '</td><td>' . esc_html( $new_value ) . '</td></tr>';
+                }
+
+                $table .= '</tbody></table>';
+
+                $this->feedback( 'compare_before_overwrite' );
+
+                if ( $is_same_theme ) {
+                        $this->feedback( 'reuploading_theme' );
+                }
+
+                // 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() );
+                }
+
+                /**
+                 * Filters the compare table output for overwrite 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, $this->upgrader->new_theme_data );
+
+                $install_actions = array(
+                        'themes_page' => sprintf(
+                                '<a href="%s" target="_parent">%s</a>',
+                                self_admin_url( 'theme-install.php' ),
+                                __( 'Cancel and go back' )
+                        ),
+                );
+
+                $can_update = true;
+
+                if ( ! empty( $this->upgrader->new_theme_data['RequiresPHP'] ) && version_compare( phpversion(), $this->upgrader->new_theme_data['RequiresPHP'], '<' ) ) {
+                        $error = sprintf(
+                                /* translators: 1: Current PHP version, 2: Version required by the uploaded theme. */
+                                __( 'The theme cannot be updated. The PHP version on your server is %1$s, however the uploaded theme requires %2$s.' ),
+                                phpversion(),
+                                $this->upgrader->new_theme_data['RequiresPHP']
+                        );
+
+                        $this->feedback( '<div class="notice notice-error inline"><p>' . esc_html( $error ) . '</p></div>' );
+                        $can_update = false;
+                }
+
+                if ( ! empty( $this->upgrader->new_theme_data['RequiresWP'] ) && version_compare( $GLOBALS['wp_version'], $this->upgrader->new_theme_data['RequiresWP'], '<' ) ) {
+                        $error = sprintf(
+                                /* translators: 1: Current WordPress version, 2: Version required by the uploaded theme. */
+                                __( 'The theme cannot be updated. Your WordPress version is %1$s, however the uploaded theme requires %2$s.' ),
+                                $GLOBALS['wp_version'],
+                                $this->upgrader->new_theme_data['RequiresWP']
+                        );
+
+                        $this->feedback( '<div class="notice notice-error inline"><p>' . esc_html( $error ) . '</p></div>' );
+                        $can_update = false;
+                }
+
+                if ( $can_update ) {
+                        $overwrite = 'update-theme';
+                        $label     = __( 'Remove current and install the uploaded version' );
+
+                        if ( $this->is_downgrading ) {
+                                $overwrite = 'downgrade-theme';
+
+                                if ( isset( $this->upgrader->new_theme_data['Version'] ) ) {
+                                        $label = sprintf( __( 'Remove current and install version %s' ), $this->upgrader->new_theme_data['Version'] );
+                                }
+                        }
+
+                        $install_actions['ovewrite_theme'] = sprintf(
+                                '<a class="ovewrite-uploaded-theme" href="%s" target="_parent">%s</a>',
+                                wp_nonce_url( add_query_arg( 'overwrite', $overwrite, $this->url ), 'theme-upload' ),
+                                esc_html( $label )
+                        );
+
+                        $warning = __( '<strong>Important:</strong> Before updating, please <a href="https://wordpress.org/support/article/wordpress-backups/">back up your database and files</a>.' );
+                        $this->feedback( '<div class="notice notice-warning inline"><p>' . $warning . '</p></div>' );
+                }
+
+                /**
+                 * Filters the list of action links available following a single theme installation failed but ovewrite 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_ovewrite_actions', $install_actions, $this->api, $this->upgrader->new_theme_data );
+                if ( ! empty( $install_actions ) ) {
+                        $this->feedback( implode( ' | ', (array) $install_actions ) );
+                }
+
+                return true;
+        }
+
 }

src/wp-admin/includes/class-theme-upgrader.php

@@ -37 +37 @@
          */
         public $bulk = false;
 
+        /**
+         * New theme info.
+         *
+         * @since 5.5.0
+         * @var array $new_theme_data
+         *
+         * @see check_package()
+         */
+        public $new_theme_data = array();
+
         /**
          * Initialize the upgrade strings.
          *
@@ -65 +75 @@
                 $this->strings['downloading_package'] = sprintf( __( 'Downloading installation package from %s&#8230;' ), '<span class="code">%s</span>' );
                 $this->strings['unpack_package']      = __( 'Unpacking the package&#8230;' );
                 $this->strings['installing_package']  = __( 'Installing the theme&#8230;' );
+                $this->strings['remove_old']          = __( 'Removing the old version of the theme&#8230;' );
+                $this->strings['remove_old_failed']   = __( 'Could not remove the old theme.' );
                 $this->strings['no_files']            = __( 'The theme contains no files.' );
                 $this->strings['process_failed']      = __( 'Theme installation failed.' );
                 $this->strings['process_success']     = __( 'Theme installed successfully.' );
@@ -79 +91 @@
                 $this->strings['parent_theme_install_success'] = __( 'Successfully installed the parent theme, <strong>%1$s %2$s</strong>.' );
                 /* translators: %s: Theme name. */
                 $this->strings['parent_theme_not_found'] = sprintf( __( '<strong>The parent theme could not be found.</strong> You will need to install the parent theme, %s, before you can use this child theme.' ), '<strong>%s</strong>' );
+
+                $this->strings['compare_before_overwrite'] = __( 'Theme information:' );
+                $this->strings['reuploading_theme']        = __( 'Seems you have uploaded a theme that is already installed.' );
+                $this->strings['current_theme_has_errors'] = __( 'The current theme has the follow error: "%s".' );
+
+                if ( 'update-theme' === $this->skin->overwrite ) {
+                        $this->strings['installing_package'] = __( 'Updating the theme&#8230;' );
+                        $this->strings['process_failed']     = __( 'Theme update failed.' );
+                        $this->strings['process_success']    = __( 'Theme updated successfully.' );
+                }
+
+                if ( 'downgrade-theme' === $this->skin->overwrite ) {
+                        $this->strings['installing_package'] = __( 'Downgrading the theme&#8230;' );
+                        $this->strings['process_failed']     = __( 'Theme downgrade failed.' );
+                        $this->strings['process_success']    = __( 'Theme downgraded successfully.' );
+                }
         }
 
         /**
@@ -200 +228 @@
          * @return bool|WP_Error True if the installation was successful, false or a WP_Error object otherwise.
          */
         public function install( $package, $args = array() ) {
-
                 $defaults    = array(
                         'clear_update_cache' => true,
+                        'overwrite_package'  => false, // Do not overwrite files.
                 );
                 $parsed_args = wp_parse_args( $args, $defaults );
 
@@ -220 +248 @@
                         array(
                                 'package'           => $package,
                                 'destination'       => get_theme_root(),
-                                'clear_destination' => false, // Do not overwrite files.
+                                'clear_destination' => $args['overwrite_package'],
                                 'clear_working'     => true,
                                 'hook_extra'        => array(
                                         'type'   => 'theme',
@@ -240 +268 @@
                 // Refresh the Theme Update information.
                 wp_clean_themes_cache( $parsed_args['clear_update_cache'] );
 
+                if ( $parsed_args['overwrite_package'] ) {
+                        /**
+                         * Fires when the upgrader process a install forcing a package overwrite.
+                         *
+                         * @since 5.5.0
+                         *
+                         * @param string  $package          The package file.
+                         * @param array   $new_plugin_data  The new theme data.
+                         * @param string  $package_type     The package type (theme or theme).
+                         */
+                        do_action( 'upgrader_overwrited_package', $package, $this->new_theme_data, 'theme' );
+                }
+
                 return true;
         }
 
@@ -259 +300 @@
          * @return bool|WP_Error True if the upgrade was successful, false or a WP_Error object otherwise.
          */
         public function upgrade( $theme, $args = array() ) {
-
                 $defaults    = array(
                         'clear_update_cache' => true,
                 );
@@ -332 +372 @@
          * @return array[]|false An array of results, or false if unable to connect to the filesystem.
          */
         public function bulk_upgrade( $themes, $args = array() ) {
-
                 $defaults    = array(
                         'clear_update_cache' => true,
                 );
@@ -461 +500 @@
         public function check_package( $source ) {
                 global $wp_filesystem;
 
+                $this->new_theme_data = array();
+
                 if ( is_wp_error( $source ) ) {
                         return $source;
                 }
@@ -484 +525 @@
                         );
                 }
 
+                // All these headers are needed on Theme_Installer_Skin::do_overwrite().
                 $info = get_file_data(
                         $working_directory . 'style.css',
                         array(
-                                'Name'     => 'Theme Name',
-                                'Template' => 'Template',
+                                'Name'        => 'Theme Name',
+                                'Version'     => 'Version',
+                                'Author'      => 'Author',
+                                'Template'    => 'Template',
+                                'RequiresWP'  => 'Requires at least',
+                                'RequiresPHP' => 'Requires PHP',
                         )
                 );
 
@@ -517 +563 @@
                         );
                 }
 
+                $this->new_theme_data = $info;
                 return $source;
         }
 
@@ -640 +687 @@
          *                        and the last result isn't set.
          */
         public function theme_info( $theme = null ) {
-
                 if ( empty( $theme ) ) {
                         if ( ! empty( $this->result['destination_name'] ) ) {
                                 $theme = $this->result['destination_name'];
@@ -648 +694 @@
                                 return false;
                         }
                 }
-                return wp_get_theme( $theme );
+
+                $theme = wp_get_theme( $theme );
+                $theme->cache_delete();
+
+                return $theme;
         }
 
 }

src/wp-admin/includes/plugin-install.php

@@ -351 +351 @@
         <form method="post" enctype="multipart/form-data" class="wp-upload-form" action="<?php echo self_admin_url( 'update.php?action=upload-plugin' ); ?>">
                 <?php wp_nonce_field( 'plugin-upload' ); ?>
                 <label class="screen-reader-text" for="pluginzip"><?php _e( 'Plugin zip file' ); ?></label>
-                <input type="file" id="pluginzip" name="pluginzip" />
+                <input type="file" id="pluginzip" name="pluginzip" accept=".zip" />
                 <?php submit_button( __( 'Install Now' ), '', 'install-plugin-submit', false ); ?>
         </form>
 </div>

src/wp-admin/includes/theme-install.php

@@ -183 +183 @@
 <form method="post" enctype="multipart/form-data" class="wp-upload-form" action="<?php echo self_admin_url( 'update.php?action=upload-theme' ); ?>">
         <?php wp_nonce_field( 'theme-upload' ); ?>
         <label class="screen-reader-text" for="themezip"><?php _e( 'Theme zip file' ); ?></label>
-        <input type="file" id="themezip" name="themezip" />
+        <input type="file" id="themezip" name="themezip" accept=".zip"/>
         <?php submit_button( __( 'Install Now' ), '', 'install-theme-submit', false ); ?>
 </form>
         <?php

src/wp-admin/update.php

@@ -162 +162 @@
                 $url   = add_query_arg( array( 'package' => $file_upload->id ), 'update.php?action=upload-plugin' );
                 $type  = 'upload'; // Install plugin type, From Web or an Upload.
 
-                $upgrader = new Plugin_Upgrader( new Plugin_Installer_Skin( compact( 'type', 'title', 'nonce', 'url' ) ) );
-                $result   = $upgrader->install( $file_upload->package );
+                $overwrite = isset( $_GET['overwrite'] ) ? sanitize_text_field( $_GET['overwrite'] ) : '';
+                $overwrite = in_array( $overwrite, array( 'update-plugin', 'downgrade-plugin' ), true ) ? $overwrite : '';
+
+                $upgrader = new Plugin_Upgrader( new Plugin_Installer_Skin( compact( 'type', 'title', 'nonce', 'url', 'overwrite' ) ) );
+                $result   = $upgrader->install( $file_upload->package, [ 'overwrite_package' => $overwrite ] );
 
                 if ( $result || is_wp_error( $result ) ) {
                         $file_upload->cleanup();
@@ -282 +285 @@
                 $url   = add_query_arg( array( 'package' => $file_upload->id ), 'update.php?action=upload-theme' );
                 $type  = 'upload'; // Install theme type, From Web or an Upload.
 
-                $upgrader = new Theme_Upgrader( new Theme_Installer_Skin( compact( 'type', 'title', 'nonce', 'url' ) ) );
-                $result   = $upgrader->install( $file_upload->package );
+                $overwrite = isset( $_GET['overwrite'] ) ? sanitize_text_field( $_GET['overwrite'] ) : '';
+                $overwrite = in_array( $overwrite, array( 'update-theme', 'downgrade-theme' ), true ) ? $overwrite : '';
+
+                $upgrader = new Theme_Upgrader( new Theme_Installer_Skin( compact( 'type', 'title', 'nonce', 'url', 'overwrite' ) ) );
+                $result   = $upgrader->install( $file_upload->package, [ 'overwrite_package' => $overwrite ] );
 
                 if ( $result || is_wp_error( $result ) ) {
                         $file_upload->cleanup();