[SLUGS] fix language autodetection

src/init.php

@@ -82,6 +82,8 @@ function qtranxf_init_language(): void {
     $url_info['language'] = qtranxf_detect_language( $url_info );
     $q_config['language'] = apply_filters( 'qtranslate_language', $url_info['language'], $url_info );
 
+    QTX_Module_Loader::load_active_modules_early_hooks();
+
     assert( isset( $q_config['url_info']['doing_front_end'] ) );
     if ( $q_config['url_info']['doing_front_end'] && qtranxf_can_redirect() ) {
         qtranxf_check_url_maybe_redirect( $url_info );

src/modules/module_loader.php

@@ -39,4 +39,24 @@ public static function load_active_modules(): void {
             }
         }
     }
+
+    /**
+     * Loads early hooks from modules previously activated in the options.
+     *
+     * Attention! This assumes the current states stored in the options are valid.
+     * This doesn't perform any check, neither on the plugin conditions nor the folder structure.
+     * In the worst case the state can be refreshed by reactivating the plugin.
+     *
+     * Note also the modules should be loaded before "qtranslate_init_language" is triggered.
+     */
+    public static function load_active_modules_early_hooks(): void {
+        $modules_state = get_option( QTX_OPTIONS_MODULES_STATE, array() );
+
+        foreach ( $modules_state as $module_id => $state ) {
+            $target = QTRANSLATE_DIR . '/src/modules/' . $module_id . '/' . 'early_hooks.php';
+            if ( $state === QTX_MODULE_STATE_ACTIVE && file_exists( $target ) ) {
+                require_once( $target );
+            }
+        }
+    }
 }

src/modules/slugs/early_hooks.php

@@ -0,0 +1,31 @@
+<?php
+
+add_filter( 'qtranslate_language_detect_redirect', 'qtranxf_slugs_language_detect_redirect', 600, 3 );
+
+/**
+* Disables default redirection when language is not detectable from url (e.g. default language url with hide_default_language activated).
+* Exception is made for site_url(), for which language detection feature is preserved.
+* 
+*
+* @see qtranxf_check_url_maybe_redirect
+* @param string $url_lang proposed target URL for the active language to redirect to.
+* @param string $url_orig original URL supplied to browser, which needs to be standardized.
+* @param array $url_info a hash of various information parsed from original URL, cookies and other site configuration. The key names should be self-explanatory.
+*
+* @return string resulting redirection url
+*/
+function qtranxf_slugs_language_detect_redirect($url_lang, $url_orig, $url_info): string {
+   global $q_config;
+   /* Make sure urls with no lang info are treated as default language, unless it's site_url */
+   if ( untrailingslashit( site_url() ) != untrailingslashit( $url_orig ) && empty( $url_info['lang_url'] ) ){
+      return qtranxf_convertURL( $url_orig, $q_config['default_language'], false, true );
+   /* The following fixes the case when the browser removes language marker from default language site url (caching?) passing directly _$SERVER['REQUEST_URI'] with language info removed.
+    * In this case is not possible to switch to default language from site url.
+    * Application of this hack is narrowed down to the cases where referer is site url in current language, to preserve language detection feature as much as possible.
+    * @TODO: check if a cleaner fix is applicable. */
+   } else if ( $q_config['hide_default_language'] && untrailingslashit( site_url() ) == untrailingslashit( $url_orig ) && untrailingslashit($url_lang) === untrailingslashit( wp_get_raw_referer() ) ) {
+      return qtranxf_convertURL( $url_orig, $q_config['default_language'], false, true );
+   }
+   /* All other cases follow default behaviour */
+      return $url_lang;
+}