Flag Global Usings in Headers with clang-tidy

A using-directive or using-declaration in the global namespace of a
header reaches every file that includes it, and a using-declaration also
makes the include checker treat that header as the one to include for
the name. google-global-names-in-headers reports both, on changed lines
like the existing check, so headers that still have one are not held to
it until the line is touched.

The check does not see a using inside a namespace.

clang_tidy_diff.py's closing message assumed every finding was a missing
include; it now says other findings need a manual fix.

.clang-tidy

@@ -1,10 +1,15 @@
 # clang-tidy configuration, enforced by the clang-tidy CI job on the lines a pull
-# request changes (scripts/clang_tidy_diff.py). Only missing includes are reported
-# for now: a file should include the header for every symbol it uses, not rely on
-# the precompiled header or another header's includes. Run with --fix to add them.
+# request changes (scripts/clang_tidy_diff.py). Two things are reported.
+# Missing includes: a file should include the header for every symbol it uses, not
+# rely on the precompiled header or another header's includes. Run with --fix to
+# add them.
+# Using-directives and using-declarations in the global namespace of a header:
+# they reach every file that includes the header, and a using-declaration also
+# makes the header look like the one to include for that name. Qualify the name
+# in the header, and put the using in the source files that want it.
 # Every check listed here gates pull requests, so enable a new one only once the
 # code it flags on touched lines is reasonable to fix in passing.
-Checks: '-*,misc-include-cleaner'
+Checks: '-*,misc-include-cleaner,google-global-names-in-headers'
 WarningsAsErrors: '*'
 CheckOptions:
   # Missing includes only. Builds without the precompiled header break on these.

scripts/clang_tidy_diff.py

@@ -311,11 +311,12 @@ def main():
         for path in fixed:
             print(f"    {path}")
     if failed and fixed:
-        print(f"\nclang-tidy still fails on {len(failed)} file(s); the findings above are what --fix could not add.")
+        print(f"\nclang-tidy still fails on {len(failed)} file(s); the findings above are what --fix could not fix.")
         return 1
     if failed:
         print(f"\nclang-tidy failed on {len(failed)} file(s). Add the includes it names, or apply its "
-              "suggestions locally with scripts/run_clang_tidy.sh --fix (scripts\\run_clang_tidy.ps1 -Fix on Windows).")
+              "suggestions locally with scripts/run_clang_tidy.sh --fix (scripts\\run_clang_tidy.ps1 -Fix on Windows). "
+              "Other findings need a manual fix.")
         return 1
     print("clang-tidy passed.")
     return 0

src/libslic3r/Fill/FillSpiralInset.cpp

@@ -352,6 +352,16 @@ void FillSpiralInset::_fill_surface_single(const FillParams& params,
     assert(params.use_arachne);
     assert(this->print_config != nullptr && this->print_object_config != nullptr);
 
+    // Internal solid infill must not add Arachne's standalone thin walls: one of those walls can
+    // become the extra centre point after the spiral has finished. Top and bottom surfaces keep
+    // Arachne, including the centre plug handled by generate_spiral_insets().
+    if (params.extrusion_role == erSolidInfill) {
+        Polylines polylines;
+        this->_fill_surface_single(params, thickness_layers, direction, expolygon, polylines);
+        append(thick_polylines_out, to_thick_polylines(std::move(polylines), scaled<coord_t>(this->spacing)));
+        return;
+    }
+
     // Only a solid surface is worth the variable width walls; a sparse one falls back to plain loops.
     if (params.density <= 0.9999f || params.dont_adjust) {
         Polylines polylines;

src/libslic3r/PerimeterGenerator.cpp

@@ -759,6 +759,59 @@ static void clip_inner_walls_over_top(std::vector<Arachne::VariableWidthLines> &
     }
 }
 
+// ORCA: only_one_wall_top - widest bead of the given walls.
+static coord_t widest_bead(const std::vector<Arachne::VariableWidthLines> &walls)
+{
+    coord_t widest = 0;
+    for (const Arachne::VariableWidthLines &group : walls)
+        for (const Arachne::ExtrusionLine &el : group)
+            for (const Arachne::ExtrusionJunction &j : el.junctions)
+                widest = std::max(widest, j.w);
+    return widest;
+}
+
+// ORCA: only_one_wall_top - length of the walls running further than tolerance from the reference walls, outside the
+// excluded area.
+static double length_off_reference(const std::vector<Arachne::VariableWidthLines> &walls, const Arachne::VariableWidthLines &reference,
+                                   const ExPolygons &excluded, coord_t tolerance)
+{
+    auto append_centerlines = [](const Arachne::VariableWidthLines &lines, Polylines &out) {
+        for (const Arachne::ExtrusionLine &el : lines) {
+            if (el.junctions.size() < 2)
+                continue;
+            Polyline &centerline = out.emplace_back();
+            centerline.points.reserve(el.junctions.size());
+            for (const Arachne::ExtrusionJunction &j : el.junctions)
+                centerline.points.emplace_back(j.p);
+        }
+    };
+    Polylines wall_centerlines;
+    Polylines reference_centerlines;
+    for (const Arachne::VariableWidthLines &group : walls)
+        append_centerlines(group, wall_centerlines);
+    append_centerlines(reference, reference_centerlines);
+
+    Polylines off_reference = diff_pl(wall_centerlines, offset(reference_centerlines, float(tolerance)));
+    if (! excluded.empty())
+        off_reference = diff_pl(off_reference, excluded);
+    return total_length(off_reference);
+}
+
+// ORCA: only_one_wall_top - area covered by the given walls at their local widths.
+static Polygons walls_footprint(const Arachne::VariableWidthLines &walls)
+{
+    Polygons footprint;
+    for (const Arachne::ExtrusionLine &el : walls)
+        for (size_t i = 1; i < el.junctions.size(); ++ i) {
+            const Arachne::ExtrusionJunction &a     = el.junctions[i - 1];
+            const Arachne::ExtrusionJunction &b     = el.junctions[i];
+            const coord_t                     width = std::max(a.w, b.w);
+            if (width > 0)
+                append(footprint, offset(Polyline(a.p, b.p), float(width) / 2.f));
+        }
+    return union_(footprint);
+}
+
 void PerimeterGenerator::split_top_surfaces(const ExPolygons &orig_polygons, ExPolygons &top_fills,
                                             ExPolygons &non_top_polygons, ExPolygons &fill_clip) const {
     // other perimeters
@@ -2546,44 +2599,90 @@ void PerimeterGenerator::process_arachne()
         if (inner_loop_number >= 0) {
             assert(upper_slices != nullptr);
 
-            // Infill contour bounding box.
-            BoundingBox infill_contour_bbox = get_extents(infill_contour);
-            infill_contour_bbox.offset(SCALED_EPSILON);
-            
             coord_t perimeter_width = this->perimeter_flow.scaled_width();
 
-            // Get top ExPolygons from current infill contour.
-            Polygons upper_slices_clipped;
-            if (object_config->interface_shells) {
-                auto upper_slicer_same_region = to_expolygons(this->upper_slices_same_region->surfaces);
-                upper_slices_clipped = ClipperUtils::clip_clipper_polygons_with_subject_bbox(upper_slicer_same_region, infill_contour_bbox);
-            } else
-                upper_slices_clipped = ClipperUtils::clip_clipper_polygons_with_subject_bbox(*upper_slices, infill_contour_bbox);
+            // Filter out areas that are too thin and expand top surface polygons a bit to hide the wall line.
+            // ORCA: skip if the top surface area is smaller than "min_width_top_surface"
+            const float top_surface_min_width = std::max<float>(float(ext_perimeter_spacing) / 4.f + scaled<float>(0.00001), float(scale_(config->min_width_top_surface.get_abs_value(unscale_(perimeter_width)))) / 4.f);
 
-            top_expolygons = diff_ex(infill_contour, upper_slices_clipped);
+            // Get top ExPolygons from the given contour. uncovered reports whether the upper layer leaves any of the
+            // contour uncovered, before bridges and too thin areas are filtered out.
+            auto get_top_expolygons = [&](const ExPolygons &contour, bool &uncovered) {
+                // Contour bounding box.
+                BoundingBox contour_bbox = get_extents(contour);
+                contour_bbox.offset(SCALED_EPSILON);
+
+                Polygons upper_slices_clipped;
+                if (object_config->interface_shells) {
+                    auto upper_slicer_same_region = to_expolygons(this->upper_slices_same_region->surfaces);
+                    upper_slices_clipped = ClipperUtils::clip_clipper_polygons_with_subject_bbox(upper_slicer_same_region, contour_bbox);
+                } else
+                    upper_slices_clipped = ClipperUtils::clip_clipper_polygons_with_subject_bbox(*upper_slices, contour_bbox);
+
+                ExPolygons top = diff_ex(contour, upper_slices_clipped);
+                uncovered      = !top.empty();
+                if (top.empty())
+                    return top;
 
-            if (!top_expolygons.empty()) {
                 if (lower_slices != nullptr) {
                     const float      bridge_offset          = float(std::max<coord_t>(ext_perimeter_spacing, perimeter_width));
-                    const Polygons   lower_slices_clipped   = ClipperUtils::clip_clipper_polygons_with_subject_bbox(*lower_slices, infill_contour_bbox);
-                    const ExPolygons current_slices_bridges = offset_ex(diff_ex(top_expolygons, lower_slices_clipped), bridge_offset);
+                    const Polygons   lower_slices_clipped   = ClipperUtils::clip_clipper_polygons_with_subject_bbox(*lower_slices, contour_bbox);
+                    const ExPolygons current_slices_bridges = offset_ex(diff_ex(top, lower_slices_clipped), bridge_offset);
 
                     // Remove bridges from top surface polygons.
-                    top_expolygons = diff_ex(top_expolygons, current_slices_bridges);
+                    top = diff_ex(top, current_slices_bridges);
                 }
 
-                // Filter out areas that are too thin and expand top surface polygons a bit to hide the wall line.
-                // ORCA: skip if the top surface area is smaller than "min_width_top_surface"
-                const float top_surface_min_width = std::max<float>(float(ext_perimeter_spacing) / 4.f + scaled<float>(0.00001), float(scale_(config->min_width_top_surface.get_abs_value(unscale_(perimeter_width)))) / 4.f);
                 // Shrink the polygon to remove the small areas, then expand it back out plus a maragin to hide the wall line a little.
                 // ORCA: Expand the polygon with half the perimeter width in addition to the contracted amount,
                 // not the full perimeter width as PS does, to enable thin lettering to print on the top surface without nozzle collisions
                 // due to thin lines being generated
-                top_expolygons = offset2_ex(top_expolygons, -top_surface_min_width, top_surface_min_width + float(perimeter_width * 0.85));
+                top = offset2_ex(top, -top_surface_min_width, top_surface_min_width + float(perimeter_width * 0.85));
 
                 // Get final top ExPolygons (bridges were excluded above, so they stay walled).
-                top_expolygons = intersection_ex(top_expolygons, infill_contour);
+                return intersection_ex(top, contour);
+            };
 
+            // Walls with the full count, as generated when the single perimeter feature is disabled. Generated on first use.
+            std::vector<Arachne::VariableWidthLines> full_perimeters;
+            Polygons                                 full_inner_contour;
+            bool                                     full_perimeters_generated = false;
+            auto generate_full_perimeters = [&]() {
+                if (full_perimeters_generated)
+                    return;
+                Arachne::WallToolPaths full_tool_paths(last_p, bead_width_0, perimeter_spacing, coord_t(inner_loop_number + 2), wall_0_inset, layer_height, input_params_tmp);
+                full_perimeters           = full_tool_paths.getToolPaths();
+                full_inner_contour        = full_tool_paths.getInnerContour();
+                full_perimeters_generated = true;
+            };
+
+            // ORCA: the single wall pass allows Arachne 2 beads across a wall, so it fills a wall narrower than 3 outer wall
+            // widths by widening both, where the full pass adds a middle bead. Over the top surface that is the intent;
+            // anywhere else it leaves no room for the inner walls. When the single wall pass's outer walls run away from
+            // the full pass's outside the top surface, take the full pass's outer walls and the area inside them instead.
+            // Walls closer than outer_wall_tolerance count as the same wall: a widened bead's centerline moves by half
+            // the width added, and only beads widened by more than twice the tolerance are looked for.
+            const coord_t outer_wall_tolerance = bead_width_0 / 10;
+            if (widest_bead(perimeters) > bead_width_0 + 2 * outer_wall_tolerance) {
+                // The single wall pass's inner contour where it widens no bead: inside nominal width outer walls.
+                const ExPolygons nominal_infill_contour = offset_ex(last, -float(bead_width_0 + wall_0_inset));
+                bool             nominal_uncovered      = false;
+                // Grown by an outer wall width to take in the outer walls bordering the top surface.
+                const ExPolygons top_zone = offset_ex(get_top_expolygons(nominal_infill_contour, nominal_uncovered), float(bead_width_0));
+                if (nominal_uncovered) {
+                    generate_full_perimeters();
+                    if (! full_perimeters.empty() && ! full_perimeters.front().empty() &&
+                        length_off_reference(perimeters, full_perimeters.front(), top_zone, outer_wall_tolerance) > double(perimeter_width)) {
+                        perimeters     = { full_perimeters.front() };
+                        infill_contour = diff_ex(nominal_infill_contour, walls_footprint(full_perimeters.front()), ApplySafetyOffset::Yes);
+                    }
+                }
+            }
+
+            bool uncovered = false;
+            top_expolygons = get_top_expolygons(infill_contour, uncovered);
+
+            if (uncovered) {
                 // ORCA: onion the real region (inside the outer wall) so the remaining walls follow the actual
                 // geometry, then cut away the parts over the top surface. Re-onioning the non-top complement
                 // instead - the fallback when there is no top fill - walls the top/non-top interface and rings
@@ -2612,11 +2711,11 @@ void PerimeterGenerator::process_arachne()
                 perimeters.insert(perimeters.end(), inner_perimeters.begin(), inner_perimeters.end());
                 infill_contour = union_ex(top_expolygons, inner_wall_tool_paths.getInnerContour());
             } else {
-                // There is no top surface ExPolygon, so we call Arachne again with parameters
-                // like when the single perimeter feature is disabled.
-                Arachne::WallToolPaths no_single_perimeter_tool_paths(last_p, bead_width_0, perimeter_spacing, coord_t(inner_loop_number + 2), wall_0_inset, layer_height, input_params_tmp);
-                perimeters     = no_single_perimeter_tool_paths.getToolPaths();
-                infill_contour = union_ex(no_single_perimeter_tool_paths.getInnerContour());
+                // There is no top surface ExPolygon, so use the walls generated like when the single perimeter
+                // feature is disabled.
+                generate_full_perimeters();
+                perimeters     = std::move(full_perimeters);
+                infill_contour = union_ex(full_inner_contour);
             }
         }
         //PS

src/slic3r/GUI/GLCanvas3D.cpp

@@ -7970,9 +7970,16 @@ void GLCanvas3D::_render_fps_overlay(int fps) const
     const float margin = 10.0f * get_scale();
     const ImVec2 display_size = ImGui::GetIO().DisplaySize;
     ImVec2 pos(display_size.x - margin, margin);
+    // Last frame's size; zero until the overlay has been shown once.
+    const ImGuiWindow* self = ImGui::FindWindowByName("###fps_overlay");
+    const float left = pos.x - (self != nullptr ? self->Size.x : 0.0f);
     // The Preview legend takes the top-right corner.
     if (const ImGuiWindow* legend = ImGui::FindWindowByName("Legend"); m_canvas_type == ECanvasType::CanvasPreview && legend != nullptr && legend->Active)
         pos = ImVec2(legend->Pos.x - margin, legend->Pos.y);
+    // The toolbar row can reach the corner on a narrow canvas; stack the overlay below it then.
+    else if (m_main_toolbar.is_enabled() &&
+             get_main_toolbar_offset() + m_main_toolbar.get_width() + m_separator_toolbar.get_width() + m_gizmos.get_scaled_total_width() + m_assemble_view_toolbar.get_width() > left)
+        pos.y = std::max(m_main_toolbar.get_height(), m_gizmos.get_scaled_total_height()) + margin;
     ImGui::SetNextWindowPos(pos, ImGuiCond_Always, ImVec2(1.0f, 0.0f));
     ImGui::SetNextWindowBgAlpha(0.35f);
     ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 8.0f * get_scale());

src/slic3r/GUI/ReleaseNote.cpp

@@ -1816,7 +1816,10 @@ void InputIpAddressDialog::set_machine_obj(MachineObject* obj)
     m_input_printer_name->GetTextCtrl()->SetLabelText(m_obj->get_dev_name());
 
     std::string img_str = DevPrinterConfigUtil::get_printer_connect_help_img(m_obj->printer_type);
-    auto diagram_bmp = create_scaled_bitmap(img_str + "_en", this, 198);
+    if (img_str.empty()) { img_str = "input_access_code_x1"; }
+
+    std::string language = wxGetApp().app_config->get("language");
+    auto diagram_bmp = create_scaled_bitmap(img_str + (language == "zh_CN" ? "_cn" : "_en"), this, 198);
     m_img_help->SetBitmap(diagram_bmp);
 
 

src/slic3r/GUI/Tab.cpp

@@ -2928,7 +2928,7 @@ void TabPrint::build()
         optgroup->append_single_option_line("skin_infill_line_width", "strength_settings_patterns#locked-zag");
         optgroup->append_single_option_line("skeleton_infill_line_width", "strength_settings_patterns#locked-zag");
         optgroup->append_single_option_line("symmetric_infill_y_axis", "strength_settings_infill#symmetric-infill-y-axis");
-        optgroup->append_single_option_line("infill_complete_top", "strength_settings_infill#infill-complete-top");
+        optgroup->append_single_option_line("infill_complete_top", "strength_settings_patterns#fill-pattern-tops");
         optgroup->append_single_option_line("infill_shift_step", "strength_settings_patterns#cross-hatch");
         optgroup->append_single_option_line("lateral_lattice_angle_1", "strength_settings_patterns#lateral-lattice");
         optgroup->append_single_option_line("lateral_lattice_angle_2", "strength_settings_patterns#lateral-lattice");

src/slic3r/GUI/wxExtensions.cpp

@@ -456,6 +456,13 @@ wxBitmap create_scaled_bitmap(  const std::string& bmp_name_in,
                                 const vector<std::string>& array_new_color/* = vector<std::string>*/)//used for semi transparent material)
 {
     static Slic3r::GUI::BitmapCache cache;
+
+    // An empty name means the caller's icon lookup failed
+    if (bmp_name_in.empty() || bmp_name_in == ".png") {
+        BOOST_LOG_TRIVIAL(error) << __FUNCTION__ << ": empty bitmap name";
+        return wxNullBitmap;
+    }
+
     if (bitmap2) {
         return create_scaled_bitmap2(bmp_name_in, cache, win, px_cnt, grayscale, resize, array_new_color);
     }

tests/fff_print/test_perimeters.cpp

@@ -19,8 +19,10 @@
 #include <cstddef>
 #include "libslic3r/libslic3r.h"
 #include "libslic3r/BoundingBox.hpp"
+#include "libslic3r/ClipperUtils.hpp"
 #include "libslic3r/ExPolygon.hpp"
 #include "libslic3r/Point.hpp"
+#include "libslic3r/Polyline.hpp"
 #include <limits>
 #include <string>
 #include <utility>
@@ -275,6 +277,124 @@ TEST_CASE("Only one wall on the first layer needs a bottom shell", "[Perimeters]
 
 namespace {
 
+// The last layer of the tab, whose top surface shares an island with the tube walls rising past it.
+const double tab_top_z = 5.0;
+
+// With the widths below the tube walls are 1.10mm wide once the precise outer wall offset (0.043mm a side) is
+// taken off. That is narrower than 3 outer wall spacings (3 x 0.377 = 1.131mm), so an Arachne pass limited to a
+// single wall fills it by widening its 2 beads, yet wide enough for the full 2 wall pass to add a middle wall
+// (from 1.062mm).
+const double narrow_wall = 1.186;
+
+// A 20x30x10 tube with narrow_wall thick walls, and a 20x8x5 tab against its -Y side.
+Print &tube_with_tab(Print &print, Model &model, const DynamicPrintConfig &config)
+{
+    ModelObject *object = model.add_object();
+    object->name = "tube_with_tab.stl";
+    object->add_volume(make_cube(20., 30., 10.), ModelVolumeType::MODEL_PART, false);
+    // Overlaps the tube wall by 0.5mm so the two parts slice as one island.
+    TriangleMesh tab = make_cube(20., 8.5, 5.);
+    tab.translate(0.f, -8.f, 0.f);
+    object->add_volume(std::move(tab), ModelVolumeType::MODEL_PART, false);
+    TriangleMesh bore = make_cube(20. - 2. * narrow_wall, 30. - 2. * narrow_wall, 12.);
+    bore.translate(float(narrow_wall), float(narrow_wall), -1.f);
+    object->add_volume(std::move(bore), ModelVolumeType::NEGATIVE_VOLUME, false);
+    object->add_instance();
+    object->ensure_on_bed();
+
+    print.auto_assign_extruders(object);
+    print.apply(model, config);
+    print.validate();
+    print.set_status_silent();
+    return print;
+}
+
+// Every width the narrow_wall arithmetic depends on, so none of them rests on a default.
+DynamicPrintConfig narrow_wall_config(bool only_one_wall_top, double top_surface_expansion)
+{
+    DynamicPrintConfig config = base_config("arachne");
+    config.set_deserialize_strict({
+        { "wall_loops",            2 },
+        { "nozzle_diameter",       "0.4" },
+        { "line_width",            0.42 },
+        { "outer_wall_line_width", 0.42 },
+        { "inner_wall_line_width", 0.45 },
+        { "min_bead_width",        "85%" },
+        { "precise_outer_wall",    true },
+        { "wall_sequence",         "inner wall/outer wall" },
+        { "only_one_wall_top",     only_one_wall_top },
+        { "top_surface_expansion", top_surface_expansion },
+    });
+    return config;
+}
+
+// Inner wall length the layer at print_z extrudes within 3mm of its +Y edge: the tube wall facing away from the tab.
+double far_wall_inner_wall_length(const Print &print, double print_z)
+{
+    for (const Layer *layer : print.objects().front()->layers()) {
+        if (std::abs(layer->print_z - print_z) > EPSILON)
+            continue;
+        BoundingBox band = get_extents(layer->lslices);
+        band.min.y()     = band.max.y() - scaled<coord_t>(3.);
+
+        Polylines inner_walls;
+        auto      collect = [&inner_walls](const ExtrusionPaths &paths) {
+            for (const ExtrusionPath &path : paths)
+                if (path.role() == erPerimeter)
+                    inner_walls.emplace_back(path.as_polyline());
+        };
+        for (const LayerRegion *region : layer->regions()) {
+            const ExtrusionEntityCollection walls = region->perimeters.flatten();
+            for (const ExtrusionEntity *entity : walls.entities) {
+                if (const auto *loop = dynamic_cast<const ExtrusionLoop*>(entity))
+                    collect(loop->paths);
+                else if (const auto *multi_path = dynamic_cast<const ExtrusionMultiPath*>(entity))
+                    collect(multi_path->paths);
+                else if (const auto *path = dynamic_cast<const ExtrusionPath*>(entity))
+                    collect({ *path });
+            }
+        }
+        return unscaled<double>(total_length(intersection_pl(inner_walls, band.polygon())));
+    }
+    return 0.;
+}
+
+} // namespace
+
+// only_one_wall_top first lays out an island with a single Arachne wall and generates the inner walls inside it.
+// On a wall narrower than 3 outer wall spacings that single wall pass widens its 2 beads to fill the wall and leaves
+// no room for the middle wall, which is only intended over the top surface. The tube walls away from the tab are not
+// under the tab's top surface, so on the tab's last layer they keep the inner wall they get with the option off.
+TEST_CASE("Only one wall on top surfaces keeps the inner walls of narrow walls away from the top surface", "[Perimeters]")
+{
+    // 0 re-onions the region beside the top surface, 2 clips the inner walls over it.
+    const double top_surface_expansion = GENERATE(0.0, 2.0);
+    CAPTURE(top_surface_expansion);
+
+    struct TabTopLayer {
+        double perimeters;
+        double far_wall_inner_walls;
+    };
+    auto tab_top_layer_for = [top_surface_expansion](bool only_one_wall_top) {
+        Print print;
+        Model model;
+        tube_with_tab(print, model, narrow_wall_config(only_one_wall_top, top_surface_expansion));
+        print.process();
+        REQUIRE_FALSE(print.objects().empty());
+        return TabTopLayer{ perimeter_length_at(print, tab_top_z), far_wall_inner_wall_length(print, tab_top_z) };
+    };
+
+    const TabTopLayer plain    = tab_top_layer_for(false);
+    const TabTopLayer one_wall = tab_top_layer_for(true);
+
+    // The option acts on this layer: the inner walls under the tab's top surface are gone.
+    REQUIRE(plain.far_wall_inner_walls > 10.);
+    CHECK(one_wall.perimeters < plain.perimeters);
+    CHECK_THAT(one_wall.far_wall_inner_walls, Catch::Matchers::WithinAbs(plain.far_wall_inner_walls, 1.0));
+}
+
+namespace {
+
 // The layer that closes the cavity of box_over_cavity(), the first one printed over air.
 const double cavity_ceiling_z = 6.2;