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.

.github/workflows/parity_nightly.yml

@@ -5,9 +5,8 @@
 #             re-sliced on its own to see whether it changes the G-code
 #   harness - the GUI-vs-CLI parity harness (metrics only, never fails)
 # Both test the latest successful build_all.yml Linux AppImage from main, with
-# sources checked out at the commit that build was made from; a manual run can
-# name another branch, or pin one build by its run id. Nothing here gates a
-# build or a PR.
+# sources checked out at the commit that build was made from. Nothing here
+# gates a build or a PR.
 name: Parity Nightly
 
 on:
@@ -21,13 +20,9 @@ on:
         required: false
         default: "main"
       build_branch:
-        description: "branch whose newest successful build_all artifact to test (a PR build is the PR merged into its base; sources are checked out at the PR head)"
+        description: "branch whose latest successful build_all artifact to test"
         required: false
         default: "main"
-      build_run_id:
-        description: "build_all run id to test instead of build_branch's newest (same PR caveat)"
-        required: false
-        default: ""
       fixtures:
         description: "harness fixture ids, space-separated (empty = all)"
         required: false
@@ -55,53 +50,14 @@ jobs:
         env:
           GH_TOKEN: ${{ github.token }}
           GH_REPO: ${{ github.repository }}
-          BRANCH: ${{ inputs.build_branch || 'main' }}
-          RUN_ID: ${{ inputs.build_run_id }}
-          SCHEDULED: ${{ github.event_name == 'schedule' }}
         run: |
           set -euo pipefail
-          if [ -n "$RUN_ID" ]; then
-            [[ $RUN_ID =~ ^[0-9]+$ ]] || { echo "build_run_id must be a numeric run id, got '$RUN_ID'" >&2; exit 1; }
-            # a pinned build is read directly, not through a search; it must come
-            # from this repository, because the later jobs check out its commit here
-            found=$(gh api "repos/$GH_REPO/actions/runs/$RUN_ID" --jq \
-              'select(.path == ".github/workflows/build_all.yml" and .conclusion == "success"
-                      and .head_repository.full_name == env.GH_REPO)
-               | "\(.id) \(.head_sha) \(.created_at)"')
-            [ -n "$found" ] || { echo "run $RUN_ID is not a successful build_all run of $GH_REPO" >&2; exit 1; }
-          else
-            # GitHub serves filtered run listings (branch=, status=, head_sha=, ...)
-            # from a search index that has returned weeks-old results, while the
-            # unfiltered listing stays current, so list unfiltered and filter here.
-            # The repository check keeps out fork PRs whose branch has the same
-            # name. A feature branch is normally built only for its PR, and a PR
-            # build compiles the PR merged into its base rather than head_sha, so
-            # a build of the branch itself (push or dispatch) is preferred when
-            # the same page has one.
-            pick='([.workflow_runs[] | select(.head_branch == env.BRANCH and .conclusion == "success"
-                    and .head_repository.full_name == env.GH_REPO)]
-                   | map(select(.event != "pull_request"))[0] // .[0])
-                  | select(.) | "\(.id) \(.head_sha) \(.created_at)"'
-            # a page of 100 runs spans about a day and a half; a manual run may
-            # target a branch that last built weeks ago
-            pages=3
-            if [ "$SCHEDULED" != true ]; then pages=20; fi
-            found=""
-            for page in $(seq "$pages"); do
-              found=$(gh api "repos/$GH_REPO/actions/workflows/build_all.yml/runs?per_page=100&page=$page" --jq "$pick")
-              if [ -n "$found" ]; then break; fi
-            done
-            [ -n "$found" ] || { echo "no successful $BRANCH build among the last $((pages * 100)) build_all runs; pass build_run_id to test an older one" >&2; exit 1; }
-          fi
-          read -r run_id head_sha created <<< "$found"
-          # the nightly fails rather than report on a stale build
-          if [ "$SCHEDULED" = true ] && [ $(( $(date +%s) - $(date -d "$created" +%s) )) -gt 172800 ]; then
-            echo "newest $BRANCH build $run_id is from $created, over 48 hours old" >&2
-            exit 1
-          fi
-          printf 'run_id=%s\nhead_sha=%s\n' "$run_id" "$head_sha" >> "$GITHUB_OUTPUT"
+          gh run list --workflow build_all.yml \
+            --branch "${{ inputs.build_branch || 'main' }}" \
+            --status success --limit 1 --json databaseId,headSha \
+            --jq '"run_id=\(.[0].databaseId)\nhead_sha=\(.[0].headSha)"' \
+            >> "$GITHUB_OUTPUT"
           cat "$GITHUB_OUTPUT"
-          echo "Testing build [$run_id](https://github.com/$GH_REPO/actions/runs/$run_id) of \`$head_sha\`, built $created" >> "$GITHUB_STEP_SUMMARY"
 
   effect:
     name: Override sweep effect stage (shard ${{ matrix.shard }})

src/OrcaSlicer.cpp

@@ -7015,6 +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);
+}