Report Per-Object Slicing Errors in the CLI

G-code generation collects errors raised per object, such as an empty
first layer, into one SlicingErrors exception whose own message is just
"Errors". The CLI's generic handler printed that word and recorded the
generic slicing error text, so a headless caller had nothing to act on.

Let Print render the per-object messages with each object's name, and have
the CLI catch SlicingErrors ahead of the generic handler, print that text
and record it as the result's error string. The exit code is unchanged. A
unit test lifts a cube off the bed and checks the message names the object.

src/OrcaSlicer.cpp

@@ -5520,28 +5520,12 @@ int CLI::run(int argc, char **argv)
                     //add the virtual object into unselect list if has
                     partplate_list.preprocess_exclude_areas(unselected, enable_wrapping_detect);
 
-                    // Filament ids given on the command line size the tower for STL input. A project
-                    // records its filament use per plate, so count there and keep its tower positions.
-                    const int  plate_count  = partplate_list.get_plate_count();
-                    const bool from_project = used_filament_set.empty();
-                    std::vector<int> plate_filament_counts(plate_count, static_cast<int>(used_filament_set.size()));
-                    if (from_project)
-                        for (int plate_index = 0; plate_index < plate_count; ++plate_index)
-                            plate_filament_counts[plate_index] = static_cast<int>(partplate_list.get_plate(plate_index)->get_extruders_under_cli(true, m_print_config).size());
-                    // A project only gets a tower the slicer will print: the prime tower enabled, and not
-                    // a by-object print unless a smooth timelapse needs it, as the per-plate arrange decides.
-                    const bool project_tower_allowed = m_print_config.option<ConfigOptionBool>("enable_prime_tower", true)->value &&
-                                                       (is_smooth_timelapse || !arrange_cfg.is_seq_print);
-                    const auto plate_needs_wipe_tower = [from_project, project_tower_allowed, is_smooth_timelapse](int filament_count) {
-                        if (!from_project)
-                            return filament_count > 0;
-                        return project_tower_allowed && (filament_count > 1 || (filament_count > 0 && is_smooth_timelapse));
-                    };
-                    const int max_filament_count = plate_count > 0 ? *std::max_element(plate_filament_counts.begin(), plate_filament_counts.end()) : 0;
-
-                    if (plate_needs_wipe_tower(max_filament_count))
+                    if (used_filament_set.size() > 0)
                     {
                         //prepare the wipe tower
+                        int plate_count = partplate_list.get_plate_count();
+                        int extruder_size = used_filament_set.size();
+
                         auto printer_structure_opt = m_print_config.option<ConfigOptionEnum<PrinterStructure>>("printer_structure");
                         // This margin only pre-adjusts the default away from the near edges;
                         // estimate_wipe_tower_polygon below computes the real clamped position.
@@ -5577,11 +5561,7 @@ int CLI::run(int argc, char **argv)
 
                         for (int bedid = 0; bedid < MAX_PLATE_COUNT; bedid++) {
                             int plate_index_valid = std::min(bedid, plate_count - 1);
-                            // Overflow beds may receive objects from any plate, so size them for the busiest one.
-                            const int extruder_size = bedid < plate_count ? plate_filament_counts[bedid] : max_filament_count;
-                            if (!plate_needs_wipe_tower(extruder_size))
-                                continue;
-                            if (bedid < plate_count && !from_project) {
+                            if (bedid < plate_count) {
                                 wipe_x_option->set_at(&wt_x_opt, plate_index_valid, 0);
                                 wipe_y_option->set_at(&wt_y_opt, plate_index_valid, 0);
                             }
@@ -7035,6 +7015,12 @@ int CLI::run(int argc, char **argv)
                                     }
                                 }
                                 sliced_info.sliced_plates.push_back(sliced_plate_info);
+                            } catch (const Slic3r::SlicingErrors &exs) {
+                                const std::string message = print_fff ? print_fff->slicing_errors_message(exs) : std::string(exs.what());
+                                BOOST_LOG_TRIVIAL(error) << "found slicing or export error for partplate " << index+1 << ": " << message;
+                                boost::nowide::cerr << message << std::endl;
+                                record_exit_reson(outfile_dir, CLI_SLICING_ERROR, index+1, message, sliced_info);
+                                flush_and_exit(CLI_SLICING_ERROR);
                             } catch (const std::exception &ex) {
                                 BOOST_LOG_TRIVIAL(error) << "found slicing or export error for partplate "<<index+1 << std::endl;
                                 boost::nowide::cerr << ex.what() << std::endl;

src/libslic3r/Print.cpp

@@ -1704,6 +1704,25 @@ StringObjectException Print::check_multi_filament_valid(const Print& print)
 
 // Precondition: Print::validate() requires the Print::apply() to be called its invocation.
 //BBS: refine seq-print validation logic
+// The exception's own message is just "Errors"; the detail is in the per-object errors,
+// whose object id is the PrintObject's.
+std::string Print::slicing_errors_message(const SlicingErrors &errors) const
+{
+    std::string message;
+    for (const SlicingError &error : errors.errors_) {
+        std::string object_name;
+        for (const PrintObject *object : m_objects)
+            if (object->id().id == error.objectId()) {
+                object_name = object->model_object()->name;
+                break;
+            }
+        if (!message.empty())
+            message += "\n";
+        message += object_name.empty() ? std::string(error.what()) : object_name + ": " + error.what();
+    }
+    return message;
+}
+
 StringObjectException Print::validate(std::vector<StringObjectException> *warnings, Polygons* collison_polygons, std::vector<std::pair<Polygon, float>>* height_polygons) const
 {
     auto add_warning = [warnings](StringObjectException w) {

src/libslic3r/Print.hpp

@@ -30,6 +30,8 @@
 
 namespace Slic3r {
 
+class SlicingErrors;
+
 class GCode;
 class Layer;
 class ModelObject;
@@ -967,6 +969,8 @@ public:
 
     // Returns an empty string if valid, otherwise returns an error message.
     StringObjectException validate(std::vector<StringObjectException> *warnings = nullptr, Polygons* collison_polygons = nullptr, std::vector<std::pair<Polygon, float>>* height_polygons = nullptr) const override;
+    // The per-object messages of a SlicingErrors, each prefixed with its object's name.
+    std::string slicing_errors_message(const SlicingErrors &errors) const;
     double              skirt_first_layer_height() const;
     Flow                brim_flow() const;
     Flow                skirt_flow() const;

tests/fff_print/test_print.cpp

@@ -505,3 +505,29 @@ TEST_CASE("Sequential printing publishes the nozzle group result", "[Print][Mult
         CHECK(gcode.find("; SEQ-ND-OK") != std::string::npos);
     }
 }
+
+TEST_CASE("Slicing errors are reported per object with the object's name", "[Print]")
+{
+    Print print;
+    Model model;
+    init_print({Slic3r::Test::cube(20.)}, print, model);
+    // Lift the cube off the bed: its first layer is empty, which G-code export reports per object.
+    ModelObject *object = model.objects.front();
+    object->name = "floating cube";
+    object->instances.front()->set_offset(object->instances.front()->get_offset() + Vec3d(0., 0., 2.));
+    print.apply(model, DynamicPrintConfig::full_print_config());
+    print.set_status_silent();
+
+    ScopedTemporaryFile temp(".gcode");
+    std::string message;
+    try {
+        print.process();
+        print.export_gcode(temp.string(), nullptr, nullptr);
+        FAIL("slicing did not report the empty first layer");
+    } catch (const SlicingErrors &errors) {
+        REQUIRE(errors.errors_.size() == 1);
+        message = print.slicing_errors_message(errors);
+    }
+    CHECK(message.rfind("floating cube: ", 0) == 0);
+    CHECK(message.find("empty first layer") != std::string::npos);
+}