CGAL corefinement vs. potentially-invalid inputs vs. attempts to fall back to Nef: error cases

README.md

Here's now to build the branch from openscad/openscad#3641 (see full build instructions)

git clone --depth 1 http://github.com/ochafik/openscad  --single-branch --branch fast_csg ochafik-openscad
cd ochafik-openscad
rm -fR objects/
qmake openscad.pro \
  CONFIG+=debug \
  CONFIG+=experimental \
  CONFIG+=info \
  QMAKE_CXXFLAGS+=-I../CGAL-5.2/include
make -j4

And here's how to trigger a weird corefinement edge-case (or bug?) that leaves a polyhedron in a state we can't build a nef from:

# See output log below
./openscad -o out.stl testdata/scad/3D/features/mirror-tests.scad --enable=fast-csg

I did try and repair the polyhedron with https://gist.github.com/ochafik/e55c52c50804bcb6f073968a57099e63, to no avail.

mirror-tests failure.log

ECHO: [fast-csg] corefinement union (12 vs. 12 facets)
ECHO: [fast-csg] corefinement union (12 vs. 12 facets)
ECHO: [fast-csg] corefinement union (12 vs. 12 facets)
ECHO: [fast-csg] corefinement union (12 vs. 12 facets)
ECHO: [fast-csg] corefinement union (20 vs. 20 facets)
ECHO: [fast-csg] corefinement union (24 vs. 20 facets)
CGAL error: assertion violation!
Expression : insert_ok || mesh_to_vertex_to_node_id[&tm][target(h,tm)]==node_id
File       : ../CGAL-5.2/include/CGAL/Polygon_mesh_processing/internal/Corefinement/Visitor.h
Line       : 303
Explanation: 
Refer to the bug-reporting instructions at https://www.cgal.org/bug_report.html
WARNING: [fast-csg] Corefinement corefinement union failed with an error: CGAL ERROR: assertion violation!
Expr: insert_ok || mesh_to_vertex_to_node_id[&tm][target(h,tm)]==node_id
File: ../CGAL-5.2/include/CGAL/Polygon_mesh_processing/internal/Corefinement/Visitor.h
Line: 303
ECHO: [fast-csg] nef union (24 vs. 20 facets)
CGAL error: assertion violation!
Expression : !s2.is_degenerate()
File       : ../CGAL-5.2/include/CGAL/Nef_3/SNC_intersection.h
Line       : 194
Explanation: 
Refer to the bug-reporting instructions at https://www.cgal.org/bug_report.html
ERROR: CGAL error in CGALUtils::applyUnion3DPolyhedron: CGAL ERROR: assertion violation!
Expr: !s2.is_degenerate()
File: ../CGAL-5.2/include/CGAL/Nef_3/SNC_intersection.h
Line: 194
Geometries in cache: 10
Geometry cache size in bytes: 6624
CGAL Polyhedrons in cache: 0
CGAL cache size in bytes: 0
Total rendering time: 0:00:00.137
Current top level object is empty.

I can't compile, I'm having:

src/value.cc:41:10: fatal error: double-conversion/double-conversion.h: No such file or directory
   41 | #include "double-conversion/double-conversion.h"

From the log you provide it seems that the input contains some degenerate faces which Nef and coref seem to complain about. Is it possible?