Fix Crash Selecting a User Printer Whose Parent Preset Is Not Loaded (#16579)

A user preset can inherit a system preset from a vendor that is not
installed. get_preset_base() returns null for it, and
get_selected_preset_base() dereferenced that unconditionally, so picking
the printer crashed while building the shared profiles notification URL.
Fall back to the selected preset itself. The create printer and create
filament dialogs had the same null dereference on such presets.

src/libslic3r/Preset.hpp

@@ -756,7 +756,14 @@ public:
     Preset&         get_edited_preset()         { return m_edited_preset; }
     const Preset&   get_edited_preset() const   { return m_edited_preset; }
 
-    const Preset& get_selected_preset_base() const { return *get_preset_base(m_presets[m_idx_selected]); }
+    // The root of the selected preset's inherits chain, or the selected preset itself when
+    // the chain names a preset that is not loaded (e.g. a vendor that is not installed).
+    const Preset& get_selected_preset_base() const
+    {
+        const Preset &selected = m_presets[m_idx_selected];
+        const Preset *base     = get_preset_base(selected);
+        return base ? *base : selected;
+    }
 
     // Return the last saved preset.
 //  const Preset&   get_saved_preset() const { return m_saved_preset; }

src/slic3r/GUI/CreatePresetsDialog.cpp

@@ -3151,7 +3151,7 @@ void CreatePrinterPresetDialog::set_current_visible_printer()
     m_printer_name_to_preset.clear();
     for (const Preset &printer_preset : printer_presets) {
         if (!printer_preset.is_visible) continue;
-        if (preset_bundle->printers.get_preset_base(printer_preset)->name != printer_preset.name) continue;
+        if (preset_bundle->printers.get_preset_base(printer_preset) != &printer_preset) continue;
         if (auto printer_model = dynamic_cast<ConfigOptionString*>(const_cast<Preset&>(printer_preset).config.option("printer_model", false))) {
             if (m_printer_name_to_preset.find(printer_model->value) == m_printer_name_to_preset.end()) {
                 printer_choice.push_back(from_u8(printer_model->value));
@@ -4962,7 +4962,7 @@ void CreatePresetForPrinterDialog::get_visible_printer_and_compatible_filament_p
                     if (filament_preset.is_default || !filament_preset.is_compatible || filament_preset.is_project_embedded) continue;
                     ConfigOptionStrings *filament_types;
                     const Preset *       filament_preset_base = m_preset_bundle->filaments.get_preset_base(filament_preset);
-                    if (filament_preset_base == &filament_preset) {
+                    if (filament_preset_base == &filament_preset || filament_preset_base == nullptr) {
                         filament_types = dynamic_cast<ConfigOptionStrings *>(const_cast<Preset *>(&filament_preset)->config.option("filament_type"));
                     } else {
                         filament_types = dynamic_cast<ConfigOptionStrings *>(const_cast<Preset *>(filament_preset_base)->config.option("filament_type"));

tests/libslic3r/test_preset_bundle_loading.cpp

@@ -1219,6 +1219,24 @@ TEST_CASE("find_preset2 auto-matches removed Generic vendor profiles to the libr
     CHECK(bundle.filaments.find_preset2("BrandX Generic PETG", /*auto_match=*/true) == nullptr);
 }
 
+TEST_CASE("The selected preset is its own base when its parent is not loaded", "[Preset]")
+{
+    PresetCollection printers(Preset::TYPE_PRINTER, Preset::printer_options(),
+                              static_cast<const PrintRegionConfig &>(FullPrintConfig::defaults()));
+    add_inmemory_preset(printers, "Printer");
+    add_inmemory_preset(printers, "User Printer", "Printer");
+    add_inmemory_preset(printers, "Orphan Printer", "Uninstalled Vendor Printer");
+
+    printers.select_preset_by_name("User Printer", true);
+    REQUIRE(printers.get_selected_preset_name() == "User Printer");
+    CHECK(printers.get_selected_preset_base().name == "Printer");
+
+    printers.select_preset_by_name("Orphan Printer", true);
+    REQUIRE(printers.get_selected_preset_name() == "Orphan Printer");
+    REQUIRE(printers.get_preset_base(printers.get_selected_preset()) == nullptr);
+    CHECK(printers.get_selected_preset_base().name == "Orphan Printer");
+}
+
 TEST_CASE("Renamed parent is normalized into a loaded preset's inherits", "[Preset][Rename]")
 {
     ScopedTemporaryDir   temp_dir;