[gnome-flashback] monitor-config-store: make parsing a bit more forgiving

[Alberts Muktupāvels <muktupavels src gnome org>]

commit e3e2278f73f3edc06328c23674d0504ac040a86f
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Mon Mar 7 07:04:17 2022 +0200

    monitor-config-store: make parsing a bit more forgiving
    
    Allow unknown XML elements inside <monitors>. This makes extending
    in the future easier.
    
    Based on mutter commit:
    https://gitlab.gnome.org/GNOME/mutter/-/commit/b74e99b10bd12fcfab34fa9d60dce42be1194ffa

 backends/gf-monitor-config-store.c | 64 ++++++++++++++++++++++++++++++++------
 1 file changed, 55 insertions(+), 9 deletions(-)
---
diff --git a/backends/gf-monitor-config-store.c b/backends/gf-monitor-config-store.c
index 7149422..945242b 100644
--- a/backends/gf-monitor-config-store.c
+++ b/backends/gf-monitor-config-store.c
@@ -127,6 +127,7 @@ G_DEFINE_QUARK (gf-monitor-config-store-error-quark,
 typedef enum
 {
   STATE_INITIAL,
+  STATE_UNKNOWN,
   STATE_MONITORS,
   STATE_CONFIGURATION,
   STATE_MIGRATED,
@@ -171,6 +172,9 @@ typedef struct
   GfLogicalMonitorConfig *current_logical_monitor_config;
   GList                  *current_disabled_monitor_specs;
 
+  ParserState             unknown_state_root;
+  int                     unknown_level;
+
   GfMonitorsConfigFlag    extra_config_flags;
 } ConfigParser;
 
@@ -199,6 +203,20 @@ is_system_config (GfMonitorsConfig *config)
   return !!(config->flags & GF_MONITORS_CONFIG_FLAG_SYSTEM_CONFIG);
 }
 
+static void
+enter_unknown_element (ConfigParser *parser,
+                       const char   *element_name,
+                       const char   *root_element_name,
+                       ParserState   root_state)
+{
+  parser->state = STATE_UNKNOWN;
+  parser->unknown_level = 1;
+  parser->unknown_state_root = root_state;
+
+  g_warning ("Unknown element <%s> under <%s>, ignoring",
+             element_name, root_element_name);
+}
+
 static void
 handle_start_element (GMarkupParseContext  *context,
                       const gchar          *element_name,
@@ -255,8 +273,10 @@ handle_start_element (GMarkupParseContext  *context,
         {
           if (!g_str_equal (element_name, "configuration"))
             {
-              g_set_error (error, G_MARKUP_ERROR, G_MARKUP_ERROR_UNKNOWN_ELEMENT,
-                           "Invalid toplevel element '%s'", element_name);
+              enter_unknown_element (parser,
+                                     element_name,
+                                     "monitors",
+                                     STATE_MONITORS);
               return;
             }
 
@@ -266,6 +286,13 @@ handle_start_element (GMarkupParseContext  *context,
           return;
         }
 
+      case STATE_UNKNOWN:
+        {
+          parser->unknown_level++;
+
+          return;
+        }
+
       case STATE_CONFIGURATION:
         {
           if (g_str_equal (element_name, "logicalmonitor"))
@@ -286,9 +313,10 @@ handle_start_element (GMarkupParseContext  *context,
             }
           else
             {
-              g_set_error (error, G_MARKUP_ERROR, G_MARKUP_ERROR_UNKNOWN_ELEMENT,
-                           "Invalid configuration element '%s'", element_name);
-              return;
+              enter_unknown_element (parser,
+                                     element_name,
+                                     "configuration",
+                                     STATE_CONFIGURATION);
             }
 
           return;
@@ -335,9 +363,10 @@ handle_start_element (GMarkupParseContext  *context,
             }
           else
             {
-              g_set_error (error, G_MARKUP_ERROR, G_MARKUP_ERROR_UNKNOWN_ELEMENT,
-                           "Invalid monitor logicalmonitor element '%s'", element_name);
-              return;
+              enter_unknown_element (parser,
+                                     element_name,
+                                     "logicalmonitor",
+                                     STATE_LOGICAL_MONITOR);
             }
 
           return;
@@ -589,6 +618,7 @@ finish_monitor_spec (ConfigParser *parser)
         }
 
       case STATE_INITIAL:
+      case STATE_UNKNOWN:
       case STATE_MONITORS:
       case STATE_CONFIGURATION:
       case STATE_MIGRATED:
@@ -829,6 +859,18 @@ handle_end_element (GMarkupParseContext  *context,
           return;
         }
 
+      case STATE_UNKNOWN:
+        {
+          parser->unknown_level--;
+          if (parser->unknown_level == 0)
+            {
+              g_assert (parser->unknown_state_root >= 0);
+              parser->state = parser->unknown_state_root;
+              parser->unknown_state_root = -1;
+            }
+          return;
+        }
+
       case STATE_MONITORS:
         {
           g_assert (g_str_equal (element_name, "monitors"));
@@ -949,6 +991,9 @@ handle_text (GMarkupParseContext  *context,
 
   switch (parser->state)
     {
+      case STATE_UNKNOWN:
+        return;
+
       case STATE_INITIAL:
       case STATE_MONITORS:
       case STATE_CONFIGURATION:
@@ -1141,7 +1186,8 @@ read_config_file (GfMonitorConfigStore  *config_store,
   parser = (ConfigParser) {
     .state = STATE_INITIAL,
     .config_store = config_store,
-    .extra_config_flags = extra_config_flags
+    .extra_config_flags = extra_config_flags,
+    .unknown_state_root = -1
   };
 
   parse_context = g_markup_parse_context_new (&config_parser,