Bug 1755974 - Fix Linux system print dialog to take the pages-per-sheet from print preview. r=dholbert

Differential Revision: https://phabricator.services.mozilla.com/D164621

widget/gtk/nsPrintDialogGTK.cpp

@@ -376,6 +376,8 @@ nsresult nsPrintDialogWidgetGTK::ImportSettings(nsIPrintSettings* aNSSettings) {
   GtkPrintSettings* settings = aNSSettingsGTK->GetGtkPrintSettings();
   GtkPageSetup* setup = aNSSettingsGTK->GetGtkPageSetup();
 
+  // Set our custom fields:
+
   bool geckoBool;
   aNSSettings->GetShrinkToFit(&geckoBool);
   gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(shrink_to_fit_toggle),
@@ -387,6 +389,11 @@ nsresult nsPrintDialogWidgetGTK::ImportSettings(nsIPrintSettings* aNSSettings) {
   gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(print_bg_images_toggle),
                                aNSSettings->GetPrintBGImages());
 
+  // Temporarily set the pages-per-sheet on the GtkPrintSettings:
+  int32_t pagesPerSide;
+  aNSSettings->GetNumPagesPerSheet(&pagesPerSide);
+  gtk_print_settings_set_number_up(settings, pagesPerSide);
+
   gtk_print_unix_dialog_set_settings(GTK_PRINT_UNIX_DIALOG(dialog), settings);
   gtk_print_unix_dialog_set_page_setup(GTK_PRINT_UNIX_DIALOG(dialog), setup);
 
@@ -423,6 +430,13 @@ nsresult nsPrintDialogWidgetGTK::ExportSettings(nsIPrintSettings* aNSSettings) {
     aNSSettings->SetPrintBGImages(gtk_toggle_button_get_active(
         GTK_TOGGLE_BUTTON(print_bg_images_toggle)));
 
+    // Move any pages-per-sheet value from the GtkPrintSettings to our
+    // nsIPrintSettings. (We handle pages-per-sheet internally and don't want
+    // the native Linux printing code to doubly apply that value!)
+    int32_t pagesPerSide = gtk_print_settings_get_number_up(settings);
+    gtk_print_settings_set_number_up(settings, 1);
+    aNSSettings->SetNumPagesPerSheet(pagesPerSide);
+
     // Try to save native settings in the session object
     nsCOMPtr<nsPrintSettingsGTK> aNSSettingsGTK(do_QueryInterface(aNSSettings));
     if (aNSSettingsGTK) {