minimal compile time check for wrong signal handler return type

src/common/camera_control.c

@@ -1677,7 +1677,7 @@ static void _camera_build_property_menu(CameraWidget *widget,
           /* construct menu item for property */
           gp_widget_get_name(child, &sk);
           GtkMenuItem *item = GTK_MENU_ITEM(gtk_menu_item_new_with_label(sk));
-          g_signal_connect(G_OBJECT(item), "activate", item_activate, user_data);
+          g_signal_connect(G_OBJECT(item), "activate", G_CALLBACK(item_activate), user_data);
           /* add submenu item to menu */
           gtk_menu_shell_append(GTK_MENU_SHELL(menu), GTK_WIDGET(item));
         }

src/control/signal.c

@@ -94,6 +94,7 @@ static void _image_geotag_destroy_callback(gpointer instance, gpointer imgs, con
   }
 }
 
+#define	G_CALLBACK(f)			 ((GCallback) (f))
 static dt_signal_description _signal_description[DT_SIGNAL_COUNT] = {
   /* Global signals */
   [DT_SIGNAL_MOUSE_OVER_IMAGE_CHANGE] = { "dt-global-mouse-over-image-change",
@@ -394,7 +395,7 @@ void dt_control_signal_connect(const dt_control_signal_t *ctlsig, dt_signal_t si
 {
   _print_trace(signal, DT_DEBUG_SIGNAL_ACT_CONNECT, "connect");
 
-  g_signal_connect(G_OBJECT(ctlsig->sink), _signal_description[signal].name, G_CALLBACK(cb), user_data);
+  g_signal_connect_data(G_OBJECT(ctlsig->sink), _signal_description[signal].name, G_CALLBACK(cb), user_data, NULL, 0);
 }
 
 void dt_control_signal_disconnect(const struct dt_control_signal_t *ctlsig, GCallback cb, gpointer user_data)

src/develop/blend_gui.c

@@ -2007,13 +2007,8 @@ static void _blendif_hide_output_channels(GtkMenuItem *menuitem,
 }
 
 static void _blendif_options_callback(GtkButton *button,
-                                      GdkEventButton *event,
                                       dt_iop_module_t *module)
 {
-  if(event->button != 1
-     && event->button != 2)
-    return;
-
   const dt_iop_gui_blend_data_t *bd = module->blend_data;
 
   if(!bd
@@ -3476,7 +3471,7 @@ void dt_iop_gui_init_blending(GtkWidget *iopw,
     gtk_widget_set_tooltip_text(presets_button, _("blending options"));
     if(bd->blendif_support)
     {
-      g_signal_connect(G_OBJECT(presets_button), "button-press-event",
+      g_signal_connect(G_OBJECT(presets_button), "clicked",
                        G_CALLBACK(_blendif_options_callback), module);
     }
     else

src/develop/imageop.c

@@ -875,9 +875,8 @@ static gboolean _rename_module_key_press(GtkWidget *entry,
   return FALSE; /* event not handled */
 }
 
-static gboolean _rename_module_resize(GtkWidget *entry,
-                                      GdkEventKey *event,
-                                      dt_iop_module_t *module)
+static void _rename_module_resize(GtkWidget *entry,
+                                  gpointer user)
 {
   int width = 0;
   GtkBorder padding;
@@ -887,8 +886,6 @@ static gboolean _rename_module_resize(GtkWidget *entry,
                                 gtk_widget_get_state_flags (entry),
                                 &padding);
   gtk_widget_set_size_request(entry, width + padding.left + padding.right + 1, -1);
-
-  return TRUE;
 }
 
 void dt_iop_gui_rename_module(dt_iop_module_t *module)
@@ -3011,7 +3008,7 @@ GtkWidget *dt_iop_gui_header_button(dt_iop_module_t *module,
   g_signal_connect(button, "enter-notify-event",
                    G_CALLBACK(_header_enter_notify_callback),
                    GINT_TO_POINTER(element));
-  g_signal_connect(button, "button-press-event", G_CALLBACK(callback), module);
+  g_signal_connect_data(button, "button-press-event", G_CALLBACK(callback), module, NULL, 0);
   dt_action_define(&module->so->actions, NULL, NULL, button, NULL);
   gtk_widget_show(button);
 

src/develop/imageop_gui.c

@@ -268,7 +268,7 @@ GtkWidget *dt_iop_togglebutton_new(dt_iop_module_t *self, const char *section, c
                                    DTGTKCairoPaintIconFunc paint, GtkWidget *box)
 {
   GtkWidget *w = dtgtk_togglebutton_new(paint, 0, NULL);
-  g_signal_connect(G_OBJECT(w), "button-press-event", callback, self);
+  g_signal_connect_data(G_OBJECT(w), "button-press-event", callback, self, NULL, 0);
 
   if(!ctrl_label)
     gtk_widget_set_tooltip_text(w, _(label));
@@ -304,7 +304,7 @@ GtkWidget *dt_iop_button_new(dt_iop_module_t *self, const gchar *label,
     gtk_label_set_ellipsize(GTK_LABEL(gtk_bin_get_child(GTK_BIN(button))), PANGO_ELLIPSIZE_END);
   }
 
-  g_signal_connect(G_OBJECT(button), "clicked", callback, (gpointer)self);
+  g_signal_connect_data(G_OBJECT(button), "clicked", callback, (gpointer)self, NULL, 0);
 
   dt_action_t *ac = dt_action_define_iop(self, NULL, label, button, &dt_action_def_button);
     dt_shortcut_register(ac, 0, 0, accel_key, mods);

src/gui/gtk.c

@@ -752,10 +752,10 @@ static gboolean _borders_scrolled(GtkWidget *widget,
   return TRUE;
 }
 
-static gboolean _scrollbar_changed(GtkWidget *widget,
-                                   gpointer user_data)
+static void _scrollbar_changed(GtkWidget *widget,
+                               gpointer user_data)
 {
-  if(darktable.gui->reset) return FALSE;
+  if(darktable.gui->reset) return;
 
   GtkAdjustment *adjustment_x =
     gtk_range_get_adjustment(GTK_RANGE(darktable.gui->scrollbars.hscrollbar));
@@ -766,8 +766,6 @@ static gboolean _scrollbar_changed(GtkWidget *widget,
   const gdouble value_y = gtk_adjustment_get_value(adjustment_y);
 
   dt_view_manager_scrollbar_changed(darktable.view_manager, value_x, value_y);
-
-  return TRUE;
 }
 
 gboolean _valid_window_placement(const gint saved_x,
@@ -1378,10 +1376,10 @@ int dt_gui_gtk_init(dt_gui_gtk_t *gui)
   gtkosx_application_set_window_menu(OSXApp, GTK_MENU_ITEM(window_root_menu));
   gtkosx_application_set_help_menu(OSXApp, GTK_MENU_ITEM(help_root_menu));
 
-  g_signal_connect(G_OBJECT(OSXApp), "NSApplicationBlockTermination",
-                   G_CALLBACK(_osx_quit_callback), NULL);
-  g_signal_connect(G_OBJECT(OSXApp), "NSApplicationOpenFile",
-                   G_CALLBACK(_osx_openfile_callback), NULL);
+  g_signal_connect_data(G_OBJECT(OSXApp), "NSApplicationBlockTermination",
+                        G_CALLBACK(_osx_quit_callback), NULL, NULL, 0);
+  g_signal_connect_data(G_OBJECT(OSXApp), "NSApplicationOpenFile",
+                        G_CALLBACK(_osx_openfile_callback), NULL, NULL, 0);
 #endif
 
 #ifdef _WIN32
@@ -4465,10 +4463,10 @@ GtkGestureSingle *(dt_gui_connect_click)(GtkWidget *widget,
   // GTK4 GtkGesture *gesture = gtk_gesture_click_new();
   //      gtk_widget_add_controller(widget, GTK_EVENT_CONTROLLER(gesture));
 
-  if(pressed) g_signal_connect(gesture, "pressed", pressed, data);
+  if(pressed) g_signal_connect(gesture, "pressed", G_CALLBACK(pressed), data);
   if(released)
   {
-    g_signal_connect(gesture, "released", released, data);
+    g_signal_connect(gesture, "released", G_CALLBACK(released), data);
     g_signal_connect(gesture, "cancel", G_CALLBACK(_gesture_cancel), NULL);
   }
 
@@ -4488,9 +4486,9 @@ GtkEventController *(dt_gui_connect_motion)(GtkWidget *widget,
 
   gtk_widget_add_events(widget, GDK_ENTER_NOTIFY_MASK | GDK_LEAVE_NOTIFY_MASK); // still needed for now by _main_do_event_keymap
 
-  if(motion) g_signal_connect(controller, "motion", motion, data);
-  if(enter) g_signal_connect(controller, "enter", enter, data);
-  if(leave) g_signal_connect(controller, "leave", leave, data);
+  if(motion) g_signal_connect(controller, "motion", G_CALLBACK(motion), data);
+  if(enter) g_signal_connect(controller, "enter", G_CALLBACK(enter), data);
+  if(leave) g_signal_connect(controller, "leave", G_CALLBACK(leave), data);
 
   return controller;
 }

src/gui/gtk.h

@@ -638,6 +638,28 @@ void dt_gui_dialog_restore_size(GtkDialog *dialog, const char *conf);
 // returns the session type at runtime
 dt_gui_session_type_t dt_gui_get_session_type(void);
 
+#if !defined(__cplusplus)
+#undef G_CALLBACK
+static inline GCallback G_CALLBACK(void *f) { return (GCallback)f; } // as a macro it gets expanded before reaching here
+#define DISABLINGPREFIXG_CALLBACK
+#define BOOLSIGNAL(s, signal) || !strcmp(s, #signal)
+#undef _Static_assert
+#undef  g_signal_connect
+#define g_signal_connect(instance, signal, c_handler, user_data) do { \
+  _Static_assert(((strlen(signal)>4 && !strcmp("event", &signal[strlen(signal)-5])) \
+    BOOLSIGNAL(signal, drag-motion) \
+    BOOLSIGNAL(signal, drag-failed) \
+    BOOLSIGNAL(signal, drag-drop) \
+    BOOLSIGNAL(signal, focus) \
+    BOOLSIGNAL(signal, draw) \
+    BOOLSIGNAL(signal, popup-menu) \
+    BOOLSIGNAL(signal, query-tooltip) \
+    BOOLSIGNAL(signal, match-selected) \
+    ) == _Generic((DISABLINGPREFIX##c_handler), gboolean(*)(): TRUE, default: FALSE), \
+    "signal " signal " return type does not match specified handler " #c_handler); \
+  g_signal_connect_data((instance), (signal), (GCallback)(c_handler), (user_data), NULL, (GConnectFlags) 0); } while(0)
+#endif // __cplusplus
+
 G_END_DECLS
 
 // clang-format off

src/gui/hist_dialog.c

@@ -374,7 +374,7 @@ int dt_gui_hist_dialog_new(dt_history_copy_item_t *d,
   }
 
   g_signal_connect(GTK_TREE_VIEW(d->items), "row-activated",
-                   (GCallback)tree_on_row_activated, GTK_WIDGET(dialog));
+                   G_CALLBACK(tree_on_row_activated), GTK_WIDGET(dialog));
   g_object_unref(liststore);
 
   g_signal_connect(dialog, "response", G_CALLBACK(_gui_hist_copy_response), d);

src/gui/presets.c

@@ -981,7 +981,7 @@ static void _edit_preset(const char *name_in, dt_iop_module_t *module)
     name = g_strdup(name_in);
 
   dt_gui_presets_show_iop_edit_dialog
-    (name, module, (GCallback)_edit_preset_final_callback, NULL, TRUE, TRUE,
+    (name, module, G_CALLBACK(_edit_preset_final_callback), NULL, TRUE, TRUE,
      FALSE, GTK_WINDOW(dt_ui_main_window(darktable.gui->ui)));
   g_free(name);
 }

src/iop/channelmixerrgb.c

@@ -2874,7 +2874,6 @@ static void _start_profiling_callback(GtkWidget *togglebutton, dt_iop_module_t *
 }
 
 static void _run_profile_callback(GtkWidget *widget,
-                                 GdkEventButton *event,
                                  dt_iop_module_t *self)
 {
   if(darktable.gui->reset) return;
@@ -2888,7 +2887,6 @@ static void _run_profile_callback(GtkWidget *widget,
 }
 
 static void _run_validation_callback(GtkWidget *widget,
-                                    GdkEventButton *event,
                                     dt_iop_module_t *self)
 {
   if(darktable.gui->reset) return;
@@ -2902,7 +2900,6 @@ static void _run_validation_callback(GtkWidget *widget,
 }
 
 static void _commit_profile_callback(GtkWidget *widget,
-                                     GdkEventButton *event,
                                      dt_iop_module_t *self)
 {
   if(darktable.gui->reset) return;
@@ -4693,22 +4690,22 @@ void gui_init(dt_iop_module_t *self)
   g->button_commit = dtgtk_button_new(dtgtk_cairo_paint_check_mark, 0, NULL);
   dt_action_define_iop(self, N_("calibrate"), N_("accept"),
                        g->button_commit, &dt_action_def_button);
-  g_signal_connect(G_OBJECT(g->button_commit), "button-press-event",
+  g_signal_connect(G_OBJECT(g->button_commit), "clicked",
                    G_CALLBACK(_commit_profile_callback), (gpointer)self);
   gtk_widget_set_tooltip_text(g->button_commit,
                               _("accept the computed profile and set it in the module"));
 
   g->button_profile = dtgtk_button_new(dtgtk_cairo_paint_refresh, 0, NULL);
   dt_action_define_iop(self, N_("calibrate"), N_("recompute"),
                        g->button_profile, &dt_action_def_button);
-  g_signal_connect(G_OBJECT(g->button_profile), "button-press-event",
+  g_signal_connect(G_OBJECT(g->button_profile), "clicked",
                    G_CALLBACK(_run_profile_callback), (gpointer)self);
   gtk_widget_set_tooltip_text(g->button_profile, _("recompute the profile"));
 
   g->button_validate = dtgtk_button_new(dtgtk_cairo_paint_softproof, 0, NULL);
   dt_action_define_iop(self, N_("calibrate"), N_("validate"),
                        g->button_validate, &dt_action_def_button);
-  g_signal_connect(G_OBJECT(g->button_validate), "button-press-event",
+  g_signal_connect(G_OBJECT(g->button_validate), "clicked",
                    G_CALLBACK(_run_validation_callback), (gpointer)self);
   gtk_widget_set_tooltip_text(g->button_validate, _("check the output delta E"));
 

src/iop/colorbalance.c

@@ -1798,7 +1798,7 @@ static void _configure_slider_blocks(gpointer instance, dt_iop_module_t *self)
   if(old_container) gtk_widget_show(new_container);
 }
 
-static void _cycle_layout_callback(GtkWidget *label, GdkEventButton *event, dt_iop_module_t *self)
+static gboolean _cycle_layout_callback(GtkWidget *label, GdkEventButton *event, dt_iop_module_t *self)
 {
   gchar *layout = dt_conf_get_string("plugins/darkroom/colorbalance/layout");
 
@@ -1809,6 +1809,7 @@ static void _cycle_layout_callback(GtkWidget *label, GdkEventButton *event, dt_i
   g_free(layout);
 
   _configure_slider_blocks(NULL, self);
+  return TRUE;
 }
 
 #define HSL_CALLBACK(which)                                                             \

src/iop/colorequal.c

@@ -2814,13 +2814,12 @@ static gboolean _area_button_release_callback(GtkWidget *widget,
   return FALSE;
 }
 
-static gboolean _area_size_callback(GtkWidget *widget,
-                                    GdkEventButton *event,
-                                    const dt_iop_module_t *self)
+static void _area_size_callback(GtkWidget *widget,
+                                GdkRectangle *allocation,
+                                const dt_iop_module_t *self)
 {
   dt_iop_colorequal_gui_data_t *g = self->gui_data;
   g->gradients_cached = FALSE;
-  return FALSE;
 }
 
 void gui_changed(dt_iop_module_t *self, GtkWidget *w, void *previous)
@@ -3033,7 +3032,7 @@ void gui_init(dt_iop_module_t *self)
                    G_CALLBACK(_area_motion_notify_callback), self);
   g_signal_connect(G_OBJECT(g->area), "scroll-event",
                    G_CALLBACK(_area_scrolled_callback), self);
-  g_signal_connect(G_OBJECT(g->area), "size_allocate",
+  g_signal_connect(G_OBJECT(g->area), "size-allocate",
                    G_CALLBACK(_area_size_callback), self);
 
   GtkWidget *box = self->widget = dt_gui_vbox(g->notebook, g->area);

src/iop/lut3d.c

@@ -1733,7 +1733,7 @@ void gui_init(dt_iop_module_t *self)
   gtk_tree_view_append_column((GtkTreeView *)g->lutname, col);
   GtkTreeSelection *selection = gtk_tree_view_get_selection((GtkTreeView *)g->lutname);
   gtk_tree_selection_set_mode(selection, GTK_SELECTION_SINGLE);
-  g->lutname_handler_id = g_signal_connect(G_OBJECT(selection), "changed", G_CALLBACK(_lutname_callback), self);
+  g->lutname_handler_id = g_signal_connect_data(G_OBJECT(selection), "changed", G_CALLBACK(_lutname_callback), self, NULL, 0);
   dt_gui_box_add(self->widget, g->lutwindow);
 
   g_signal_connect(G_OBJECT(g->lutentry), "changed", G_CALLBACK(_entry_callback), self);

src/iop/overlay.c

@@ -734,9 +734,9 @@ void process(dt_iop_module_t *self,
   dt_free_align(buf);
 }
 
-static void _draw_thumb(GtkWidget *area,
-                        cairo_t *crf,
-                        const dt_iop_module_t *self)
+static gboolean _draw_thumb(GtkWidget *area,
+                            cairo_t *crf,
+                            const dt_iop_module_t *self)
 {
   const dt_iop_overlay_gui_data_t *g = self->gui_data;
   const dt_iop_overlay_params_t *p = self->params;
@@ -807,6 +807,7 @@ static void _draw_thumb(GtkWidget *area,
     pango_font_description_free(desc);
     g_object_unref(layout);
   }
+  return FALSE;
 }
 
 static void _alignment_callback(const GtkWidget *tb, dt_iop_module_t *self)

src/iop/temperature.c

@@ -2011,9 +2011,9 @@ static void _gui_sliders_update(dt_iop_module_t *self)
   gtk_widget_set_visible(GTK_WIDGET(g->scale_y), (img->flags & DT_IMAGE_4BAYER));
 }
 
-static void temp_label_click(GtkWidget *label,
-                             GdkEventButton *event,
-                             dt_iop_module_t *self)
+static gboolean temp_label_click(GtkWidget *label,
+                                 GdkEventButton *event,
+                                 dt_iop_module_t *self)
 {
   dt_iop_temperature_gui_data_t *g = self->gui_data;
 
@@ -2043,6 +2043,7 @@ static void temp_label_click(GtkWidget *label,
   _color_temptint_sliders(self);
   _color_rgb_sliders(self);
   _color_finetuning_slider(self);
+  return TRUE;
 }
 
 static void _preference_changed(gpointer instance, dt_iop_module_t *self)

src/libs/collect.c

@@ -588,13 +588,13 @@ static void view_popup_menu(GtkWidget *treeview,
 
   menuitem = gtk_menu_item_new_with_label(_("update path to files..."));
   g_signal_connect(menuitem, "activate",
-                   (GCallback)view_popup_menu_onSearchFilmroll, treeview);
+                   G_CALLBACK(view_popup_menu_onSearchFilmroll), treeview);
   gtk_menu_shell_append(GTK_MENU_SHELL(menu), menuitem);
 
   menuitem = gtk_menu_item_new_with_label(_("remove..."));
   gtk_menu_shell_append(GTK_MENU_SHELL(menu), menuitem);
   g_signal_connect(menuitem, "activate",
-                   (GCallback)view_popup_menu_onRemove, treeview);
+                   G_CALLBACK(view_popup_menu_onRemove), treeview);
 
   gtk_widget_show_all(GTK_WIDGET(menu));