Fix of SPE-753

Slicer crash when SLA printer is selected and printer profile is changed

First, there was a bug in the preset Tabs, where a "printer_technology"
was incorrectly queried on "print" and "filament"
(or "sla_print" and "sla_material") profiles.

Second, there was an unsafe "printer_technology" getter, which would add
the missing key to the config container when queried for.

1 files changed, 11 insertions, 3 deletions

diff --git a/src/slic3r/GUI/Preset.hpp b/src/slic3r/GUI/Preset.hpp
index 24112cf10..021fea22c 100644
--- a/src/slic3r/GUI/Preset.hpp
+++ b/src/slic3r/GUI/Preset.hpp
@@ -161,9 +161,17 @@ public:
     }
     const std::string&  compatible_printers_condition() const { return const_cast<Preset*>(this)->compatible_printers_condition(); }
 
-    static PrinterTechnology& printer_technology(DynamicPrintConfig &cfg) { return cfg.option<ConfigOptionEnum<PrinterTechnology>>("printer_technology", true)->value; }
-    PrinterTechnology&        printer_technology() { return Preset::printer_technology(this->config); }
-    const PrinterTechnology&  printer_technology() const { return Preset::printer_technology(const_cast<Preset*>(this)->config); }
+    // Return a printer technology, return ptFFF if the printer technology is not set.
+    static PrinterTechnology printer_technology(const DynamicPrintConfig &cfg) {
+        auto *opt = cfg.option<ConfigOptionEnum<PrinterTechnology>>("printer_technology");
+        // The following assert may trigger when importing some legacy profile, 
+        // but it is safer to keep it here to capture the cases where the "printer_technology" key is queried, where it should not.
+        assert(opt != nullptr);
+        return (opt == nullptr) ? ptFFF : opt->value;
+    }
+    PrinterTechnology   printer_technology() const { return Preset::printer_technology(this->config); }
+    // This call returns a reference, it may add a new entry into the DynamicPrintConfig.
+    PrinterTechnology&  printer_technology_ref() { return this->config.option<ConfigOptionEnum<PrinterTechnology>>("printer_technology", true)->value; }
 
     // Mark this preset as compatible if it is compatible with active_printer.
     bool                update_compatible(const Preset &active_printer, const DynamicPrintConfig *extra_config, const Preset *active_print = nullptr);