Added test case to cover https://github.com/slic3r/Slic3r/issues/4497

src/CMakeLists.txt

@@ -213,6 +213,7 @@ set(SLIC3R_TEST_SOURCES
     ${TESTDIR}/libslic3r/test_skirt_brim.cpp
     ${TESTDIR}/libslic3r/test_test_data.cpp
     ${TESTDIR}/libslic3r/test_geometry.cpp
+    ${TESTDIR}/libslic3r/test_gcodewriter.cpp
 )
 
 add_executable(slic3r slic3r.cpp)

src/test/inputs/test_gcodewriter/config_lift_unlift.ini

@@ -0,0 +1,38 @@
+# generated by Slic3r 1.3.1-dev on 2018-07-27 01:40:55
+before_layer_gcode = 
+between_objects_gcode = 
+end_filament_gcode = "; Filament-specific end gcode \n;END gcode for filament\n"
+end_gcode = M104 S0 ; turn off temperature\nG28 X0  ; home X axis\nM84     ; disable motors\n
+extrusion_axis = E
+extrusion_multiplier = 1
+filament_cost = 0
+filament_density = 0
+filament_diameter = 3
+filament_max_volumetric_speed = 0
+filament_notes = ""
+gcode_comments = 0
+gcode_flavor = reprap
+label_printed_objects = 0
+layer_gcode = 
+max_print_speed = 80
+max_volumetric_speed = 0
+notes = 
+pressure_advance = 0
+printer_notes = 
+retract_length = 2
+retract_length_toolchange = 10
+retract_lift = 1.5
+retract_lift_above = 0
+retract_lift_below = 0
+retract_restart_extra = 0
+retract_restart_extra_toolchange = 0
+retract_speed = 40
+start_filament_gcode = "; Filament gcode\n"
+start_gcode = G28 ; home all axes\nG1 Z5 F5000 ; lift nozzle\n
+toolchange_gcode = 
+travel_speed = 130
+use_firmware_retraction = 0
+use_relative_e_distances = 0
+use_set_and_wait_bed = 0
+use_set_and_wait_extruder = 0
+use_volumetric_e = 0

src/test/libslic3r/test_gcodewriter.cpp

@@ -0,0 +1,37 @@
+#include <catch.hpp>
+#include <memory>
+
+#include "GCodeWriter.hpp"
+#include "test_options.hpp"
+
+using namespace Slic3r;
+using namespace std::literals::string_literals;
+
+SCENARIO("lift() is not ignored after unlift() at large values of Z", "[!mayfail]") {
+    GIVEN("A config from a file and a single extruder.")
+    auto writer {std::make_unique(GCodeWriter())}; // ensure cleanup later
+    auto& config {writer->config};
+    config.set_defaults();
+    config.load(std::string(testfile_dir) + "test_gcodewriter/config_lift_unlift.ini"s);
+
+    std::vector<unsigned int> extruder_ids {0};
+    writer->set_extruders(extruder_ids);
+    writer->set_extruder(0);
+
+    double trouble_Z = 9007199254740992;
+    WHEN("Z is set to 9007199254740992") {
+        writer->travel_to_z(trouble_Z);
+        AND_WHEN("GcodeWriter::Lift() is called") {
+            REQUIRE(writer->lift().size() > 0);
+            AND_WHEN("Z is moved post-lift to the same delta as the config Z lift") {
+                writer->travel_to_z(trouble_z + config.retract_lift);
+                AND_WHEN("GCodeWriter::Lift() is called after GCodeWriter::Unlift()") {
+                    REQUIRE(writer->unlift().size() > 0);
+                    THEN("GCodeWriter::Lift() emits gcode.") {
+                        REQUIRE(writer->lift().size() > 0);
+                    }
+                }
+            }
+        }
+    }
+}