Add a notification when custom support enforcers are not used due to supports being off

It is now emitted from Print::validate and has a hyperlink to enable supports

src/libslic3r/Print.cpp

@@ -1245,7 +1245,7 @@ static inline bool sequential_print_vertical_clearance_valid(const Print &print)
 }
 
 // Precondition: Print::validate() requires the Print::apply() to be called its invocation.
-std::string Print::validate() const
+std::string Print::validate(std::string* warning) const
 {
     if (m_objects.empty())
         return L("All objects are outside of the print volume.");
@@ -1440,7 +1440,22 @@ std::string Print::validate() const
     				}
                 }
             }
-            
+
+            // Do we have custom support data that would not be used?
+            // Notify the user in that case.
+            if (! object->has_support() && warning) {
+                for (const ModelVolume* mv : object->model_object()->volumes) {
+                    bool has_enforcers = mv->is_support_enforcer()
+                        || (mv->is_model_part()
+                            && ! mv->supported_facets.empty()
+                            && ! mv->supported_facets.get_facets(*mv, EnforcerBlockerType::ENFORCER).indices.empty());
+                    if (has_enforcers) {
+                        *warning = "_SUPPORTS_OFF";
+                        break;
+                    }
+                }
+            }
+
             // validate first_layer_height
             double first_layer_height = object->config().get_abs_value("first_layer_height");
             double first_layer_min_nozzle_diameter;

src/libslic3r/Print.hpp

@@ -444,7 +444,7 @@ public:
     bool                has_brim() const;
 
     // Returns an empty string if valid, otherwise returns an error message.
-    std::string         validate() const override;
+    std::string         validate(std::string* warning = nullptr) const override;
     double              skirt_first_layer_height() const;
     Flow                brim_flow() const;
     Flow                skirt_flow() const;

src/libslic3r/PrintBase.hpp

@@ -366,7 +366,7 @@ public:
     virtual std::vector<ObjectID> print_object_ids() const = 0;
 
     // Validate the print, return empty string if valid, return error if process() cannot (or should not) be started.
-    virtual std::string     validate() const { return std::string(); }
+    virtual std::string     validate(std::string* warning = nullptr) const { return std::string(); }
 
     enum ApplyStatus {
         // No change after the Print::apply() call.

src/libslic3r/PrintObject.cpp

@@ -430,6 +430,24 @@ void PrintObject::generate_support_material()
                 if (layer->empty())
                     throw Slic3r::SlicingError("Levitating objects cannot be printed without supports.");
 #endif
+
+            // Do we have custom support data that would not be used?
+            // Notify the user in that case.
+            if (! this->has_support()) {
+                for (const ModelVolume* mv : this->model_object()->volumes) {
+                    bool has_enforcers = mv->is_support_enforcer()
+                        || (mv->is_model_part()
+                            && ! mv->supported_facets.empty()
+                            && ! mv->supported_facets.get_facets(*mv, EnforcerBlockerType::ENFORCER).indices.empty());
+                    if (has_enforcers) {
+                        this->active_step_add_warning(PrintStateBase::WarningLevel::CRITICAL,
+                            L("An object has custom support enforcers which will not be used "
+                              "because supports are off. Consider turning them on.") + "\n" +
+                            (L("Object name")) + ": " + this->model_object()->name);
+                        break;
+                    }
+                }
+            }
         }
         this->set_done(posSupportMaterial);
     }

src/libslic3r/SLAPrint.cpp

@@ -617,7 +617,7 @@ std::string SLAPrint::output_filename(const std::string &filename_base) const
     return this->PrintBase::output_filename(m_print_config.output_filename_format.value, ".sl1", filename_base, &config);
 }
 
-std::string SLAPrint::validate() const
+std::string SLAPrint::validate(std::string*) const
 {
     for(SLAPrintObject * po : m_objects) {
 

src/libslic3r/SLAPrint.hpp

@@ -458,7 +458,7 @@ public:
 
     const SLAPrintStatistics&   print_statistics() const { return m_print_statistics; }
 
-    std::string validate() const override;
+    std::string validate(std::string* warning = nullptr) const override;
 
     // An aggregation of SliceRecord-s from all the print objects for each
     // occupied layer. Slice record levels dont have to match exactly.