build: Add -Wnull-dereference

Sprinkle various g_assert() around the code where gcc cannot figure out
on its own that a variable is not NULL and too much refactoring would be
needed to make it do that.

Also fix usage of g_assert_nonnull(x) to use g_assert(x) because the
first is not marked as G_GNUC_NORETURN because of course GTester
supports not aborting on aborts.

gdk/wayland/gdkdevice-wayland.c

@@ -4118,6 +4118,7 @@ tablet_pad_handle_button (void                     *data,
                        wp_tablet_pad, button, state));
 
   group = tablet_pad_lookup_button_group (pad, button);
+  g_assert (group != NULL);
   n_group = g_list_index (pad->mode_groups, group);
 
   event = gdk_event_pad_button_new (state == ZWP_TABLET_PAD_V2_BUTTON_STATE_PRESSED

gdk/wayland/gdkdisplay-wayland.c

@@ -1505,15 +1505,19 @@ update_xft_settings (GdkDisplay *display)
       TranslationEntry *entry;
 
       entry = find_translation_entry_by_schema ("org.gnome.settings-daemon.plugins.xsettings", "antialiasing");
+      g_assert (entry);
       antialiasing = entry->fallback.i;
 
       entry = find_translation_entry_by_schema ("org.gnome.settings-daemon.plugins.xsettings", "hinting");
+      g_assert (entry);
       hinting = entry->fallback.i;
 
       entry = find_translation_entry_by_schema ("org.gnome.settings-daemon.plugins.xsettings", "rgba-order");
+      g_assert (entry);
       order = entry->fallback.i;
 
       entry = find_translation_entry_by_schema ("org.gnome.desktop.interface", "text-scaling-factor");
+      g_assert (entry);
       dpi = 96.0 * entry->fallback.i / 65536.0 * 1024; /* Xft wants 1/1024th of an inch */
     }
   else

gdk/x11/gdkdisplay-x11.c

@@ -2673,7 +2673,11 @@ gdk_x11_display_error_trap_pop_internal (GdkDisplay *display,
         break;
     }
 
-  g_return_val_if_fail (trap != NULL, Success);
+  if (trap == NULL)
+    {
+      g_critical ("gdk_x11_display_error_trap_pop() called without gdk_x11_display_error_trap_push()");
+      return Success;
+    }
   g_assert (trap->end_sequence == 0);
 
   /* May need to sync to fill in trap->error_code if we care about

gdk/x11/gdksurface-x11.c

@@ -129,7 +129,7 @@ _gdk_x11_surface_get_toplevel (GdkSurface *surface)
 {
   GdkX11Surface *impl;
   
-  g_return_val_if_fail (GDK_IS_SURFACE (surface), NULL);
+  g_assert (GDK_IS_SURFACE (surface));
 
   impl = GDK_X11_SURFACE (surface);
 

gsk/gl/gskgldriver.c

@@ -658,7 +658,7 @@ gsk_gl_driver_mark_texture_permanent (GskGLDriver *self,
 {
   Texture *t = gsk_gl_driver_get_texture (self, texture_id);
 
-  g_assert_nonnull (t);
+  g_assert (t != NULL);
 
   t->permanent = TRUE;
 }

gtk/gtkaccelmap.c

@@ -332,6 +332,7 @@ internal_change_entry (const gchar    *accel_path,
 	{
 	  gtk_accel_map_add_entry (accel_path, 0, 0);
 	  entry = accel_path_lookup (accel_path);
+          g_assert (entry);
 	  entry->accel_key = accel_key;
 	  entry->accel_mods = accel_mods;
 	  entry->changed = TRUE;

gtk/gtkbuilderparser.c

@@ -382,8 +382,7 @@ state_pop (ParserData *data)
 {
   gpointer old = NULL;
 
-  if (!data->stack)
+  g_assert (data->stack);
-    return NULL;
 
   old = data->stack->data;
   data->stack = g_slist_delete_link (data->stack, data->stack);

gtk/gtkicontheme.c

@@ -4082,6 +4082,7 @@ gtk_icon_theme_lookup_by_gicon (GtkIconTheme       *self,
   /* We can't render emblemed icons atm, but at least render the base */
   while (G_IS_EMBLEMED_ICON (gicon))
     gicon = g_emblemed_icon_get_icon (G_EMBLEMED_ICON (gicon));
+  g_assert (gicon); /* shut up gcc -Wnull-dereference */
 
   if (GDK_IS_PIXBUF (gicon))
     {

gtk/gtkmenutracker.c

@@ -234,6 +234,7 @@ gtk_menu_tracker_item_visibility_changed (GtkMenuTrackerItem *item,
 
   /* remember: the item is our model */
   section = gtk_menu_tracker_section_find_model (tracker->toplevel, item, &offset);
+  g_assert (section);
 
   was_visible = section->items != NULL;
 
@@ -424,6 +425,7 @@ gtk_menu_tracker_model_changed (GMenuModel *model,
    * position of that section within the overall menu.
    */
   section = gtk_menu_tracker_section_find_model (tracker->toplevel, model, &offset);
+  g_assert (section);
 
   /* Next, seek through that section to the change point.  This gives us
    * the correct GSList** to make the change to and also finds the final

gtk/gtkpathbar.c

@@ -690,6 +690,7 @@ gtk_path_bar_scroll_down (GtkPathBar *path_bar)
 	  break;
 	}
     }
+  g_assert (down_button);
 
   gtk_widget_get_allocation (GTK_WIDGET (path_bar), &allocation);
   gtk_widget_get_allocation (BUTTON_DATA (down_button->data)->button, &button_allocation);

gtk/gtkrbtree.c

@@ -441,6 +441,7 @@ gtk_rb_tree_remove_node_fixup (GtkRbTree *tree,
 	      gtk_rb_node_rotate_left (tree, p);
 	      w = p->right;
 	    }
+          g_assert (w);
 	  if (is_black (w->left) && is_black (w->right))
 	    {
 	      set_red (w);
@@ -472,6 +473,7 @@ gtk_rb_tree_remove_node_fixup (GtkRbTree *tree,
 	      gtk_rb_node_rotate_right (tree, p);
 	      w = p->left;
 	    }
+          g_assert (w);
 	  if (is_black (w->right) && is_black (w->left))
 	    {
 	      set_red (w);

gtk/gtkshortcutssection.c

@@ -693,6 +693,7 @@ gtk_shortcuts_section_reflow_groups (GtkShortcutsSection *self)
           n += height;
         }
 
+      g_assert (g);
       for (g = g->next; g; g = g->next)
         {
           GtkShortcutsGroup *group = g->data;

gtk/gtktextbtree.c

@@ -2849,8 +2849,9 @@ _gtk_text_btree_set_mark (GtkTextBTree *tree,
   seg = real_set_mark (tree, existing_mark,
                        name, left_gravity, iter, should_exist,
                        TRUE);
+  g_assert (seg);
 
-  return seg ? seg->body.mark.obj : NULL;
+  return seg->body.mark.obj;
 }
 
 gboolean
@@ -3126,7 +3127,7 @@ _gtk_text_btree_last_could_contain_tag (GtkTextBTree *tree,
     {
       info = gtk_text_btree_get_existing_tag_info (tree, tag);
 
-      if (info->tag_root == NULL)
+      if (info == NULL || info->tag_root == NULL)
         return NULL;
 
       node = info->tag_root;
@@ -3135,7 +3136,6 @@ _gtk_text_btree_last_could_contain_tag (GtkTextBTree *tree,
 
       while (node->level > 0)
         {
-          g_assert (node != NULL); /* Failure probably means bad tag summaries. */
           last_node = NULL;
           node = node->children.node;
           while (node != NULL)
@@ -3146,6 +3146,7 @@ _gtk_text_btree_last_could_contain_tag (GtkTextBTree *tree,
             }
 
           node = last_node;
+          g_assert (node != NULL); /* Failure probably means bad tag summaries. */
         }
 
       g_assert (node != NULL); /* The tag summaries said some node had
@@ -3450,6 +3451,7 @@ ensure_end_iter_segment (GtkTextBTree *tree)
             last_with_chars = seg;
           seg = seg->next;
         }
+      g_assert (last_with_chars);
 
       tree->end_iter_segment = last_with_chars;
 
@@ -4455,10 +4457,6 @@ _gtk_text_line_next_could_contain_tag (GtkTextLine  *line,
 
   while (node->level > 0)
     {
-      g_assert (node != NULL); /* If this fails, it likely means an
-                                  incorrect tag summary led us on a
-                                  wild goose chase down this branch of
-                                  the tree. */
       node = node->children.node;
       while (node != NULL)
         {
@@ -4466,6 +4464,10 @@ _gtk_text_line_next_could_contain_tag (GtkTextLine  *line,
             break;
           node = node->next;
         }
+      g_assert (node != NULL); /* If this fails, it likely means an
+                                  incorrect tag summary led us on a
+                                  wild goose chase down this branch of
+                                  the tree. */
     }
 
   g_assert (node != NULL);

gtk/gtktextiter.c

@@ -209,6 +209,8 @@ gtk_text_iter_make_real (const GtkTextIter *_iter)
   GtkTextRealIter *iter;
 
   iter = gtk_text_iter_make_surreal (_iter);
+  if (iter == NULL)
+    return NULL;
 
   if (iter->segments_changed_stamp !=
       _gtk_text_btree_get_segments_changed_stamp (iter->tree))
@@ -242,8 +244,8 @@ iter_init_common (GtkTextIter *_iter,
 {
   GtkTextRealIter *iter = (GtkTextRealIter*)_iter;
 
-  g_return_val_if_fail (iter != NULL, NULL);
+  g_assert (iter != NULL);
-  g_return_val_if_fail (tree != NULL, NULL);
+  g_assert (tree != NULL);
 
   memset (iter, 0, sizeof (GtkTextRealIter));
 

gtk/gtktreemodelfilter.c

@@ -3002,6 +3002,7 @@ gtk_tree_model_filter_get_iter_full (GtkTreeModel *model,
         }
 
       elt = GET_ELT (siter);
+      g_assert (elt);
 
       if (!elt->children)
         gtk_tree_model_filter_build_level (filter, level, elt, FALSE);
@@ -3072,6 +3073,7 @@ gtk_tree_model_filter_get_iter (GtkTreeModel *model,
         }
 
       elt = GET_ELT (siter);
+      g_assert (elt);
       if (!elt->children)
         gtk_tree_model_filter_build_level (filter, level, elt, FALSE);
       level = elt->children;
@@ -4192,6 +4194,7 @@ gtk_tree_model_filter_convert_path_to_child_path (GtkTreeModelFilter *filter,
         }
 
       elt = GET_ELT (siter);
+      g_assert (elt);
       if (elt->children == NULL)
         gtk_tree_model_filter_build_level (filter, level, elt, FALSE);
 

gtk/gtktreemodelsort.c

@@ -1285,6 +1285,7 @@ gtk_tree_model_sort_get_iter (GtkTreeModel *tree_model,
         }
 
       elt = GET_ELT (siter);
+      g_assert (elt);
       if (elt->children == NULL)
 	gtk_tree_model_sort_build_level (tree_model_sort, level, elt);
 
@@ -2395,6 +2396,7 @@ gtk_tree_model_sort_convert_path_to_child_path (GtkTreeModelSort *tree_model_sor
         }
 
       elt = GET_ELT (siter);
+      g_assert (elt);
       if (elt->children == NULL)
 	gtk_tree_model_sort_build_level (tree_model_sort, level, elt);
 

gtk/gtktreerbtree.c

@@ -269,6 +269,7 @@ gtk_tree_rbtree_remove_node_fixup (GtkTreeRBTree *tree,
               gtk_tree_rbnode_rotate_left (tree, parent);
               w = parent->right;
             }
+          g_assert (w);
           if (GTK_TREE_RBNODE_GET_COLOR (w->left) == GTK_TREE_RBNODE_BLACK && GTK_TREE_RBNODE_GET_COLOR (w->right) == GTK_TREE_RBNODE_BLACK)
             {
               GTK_TREE_RBNODE_SET_COLOR (w, GTK_TREE_RBNODE_RED);
@@ -300,6 +301,7 @@ gtk_tree_rbtree_remove_node_fixup (GtkTreeRBTree *tree,
               gtk_tree_rbnode_rotate_right (tree, parent);
               w = parent->left;
             }
+          g_assert (w);
           if (GTK_TREE_RBNODE_GET_COLOR (w->right) == GTK_TREE_RBNODE_BLACK && GTK_TREE_RBNODE_GET_COLOR (w->left) == GTK_TREE_RBNODE_BLACK)
             {
               GTK_TREE_RBNODE_SET_COLOR (w, GTK_TREE_RBNODE_RED);
@@ -1595,6 +1597,8 @@ gtk_tree_rbtree_test_dirty (GtkTreeRBTree *tree,
                             GtkTreeRBNode *node,
                             gint           expected_dirtyness)
 {
+  g_assert (node);
+
   if (expected_dirtyness)
     {
       g_assert (GTK_TREE_RBNODE_FLAG_SET (node, GTK_TREE_RBNODE_COLUMN_INVALID) ||

meson.build

@@ -251,6 +251,7 @@ elif cc.get_id() == 'gcc' or cc.get_id() == 'clang'
     '-Wmissing-include-dirs',
     '-Wmissing-noreturn',
     '-Wnested-externs',
+    '-Wnull-dereference',
     '-Wold-style-definition',
     '-Wpointer-arith',
     '-Wshadow',