Ticket #39295: 39295.diff

src/wp-includes/l10n.php

@@ -96 +96 @@
                 $user = get_user_by( 'id', $user_id );
         }
 
-        if ( ! $user ) {
+        if ( ! $user || empty( $user->locale ) ) {
+                if ( doing_filter( 'locale' ) ) {
+                        _doing_it_wrong( __FUNCTION__, __( "It can not be added as a 'locale' filter, or be called by a 'locale' filter." ), '4.7.1' );
+                        return 'en_US';
+                }
+
                 return get_locale();
         }
 
-        $locale = $user->locale;
-        return $locale ? $locale : get_locale();
+        return $user->locale;
 }
 
 /**

tests/phpunit/tests/l10n/getUserLocale.php

@@ -127 +127 @@
                 $user_locale = get_user_locale( 'string' );
                 $this->assertSame( get_locale(), $user_locale );
         }
+
+        public function test_get_user_locale_as_locale_filter_triggers_doing_it_wrong() {
+                wp_set_current_user( 0 );
+                switch_to_locale( 'de_DE');
+                $this->assertSame( 'de_DE', get_user_locale() );
+
+
+                add_filter( 'locale', 'get_user_locale' );
+                $this->setExpectedIncorrectUsage( 'get_user_locale' );
+                $this->assertSame( 'en_US', get_user_locale() );
+                remove_filter( 'locale', 'get_user_locale' );
+
+                restore_current_locale();
+        }
 }