bug-fix CDT_3 (#9081)

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## Summary of Changes

_Describe what your pull request changes to CGAL (this can be skipped if
it solves an issue already in the tracker or if it is a Feature or Small
Feature submitted to the CGAL Wiki)._

## Release Management

* Affected package(s):
* Issue(s) solved (if any): fix #0000, fix #0000,...
* Feature/Small Feature (if any):
* Link to compiled documentation (obligatory for small feature) [*wrong
link name to be changed*](httpssss://wrong_URL_to_be_changed/Manual/Pkg)
* License and copyright ownership:

Author: sloriot

Constrained_triangulation_3/include/CGAL/Conforming_Delaunay_triangulation_3.h

@@ -369,6 +369,10 @@ class Conforming_Delaunay_triangulation_3 : public T_3 {
     return debug_flags[static_cast<int>(Debug_flags::use_older_cavity_algorithm)];
   }
 
+  bool use_newer_cavity_algorithm() const {
+    return !debug_flags[static_cast<int>(Debug_flags::use_older_cavity_algorithm)];
+  }
+
   void use_older_cavity_algorithm(bool b) {
     debug_flags.set(static_cast<int>(Debug_flags::use_older_cavity_algorithm), b);
   }

Constrained_triangulation_3/include/CGAL/Conforming_constrained_Delaunay_triangulation_3.h

@@ -48,7 +48,7 @@ decltype(auto) cdt_3_format(std::string_view fmt, const Args&... args) {
 
 template <typename... Args>
 constexpr decltype(auto) cdt_3_format(Args&&...) {
-  return "";
+  return std::string{};
 }
 
 constexpr bool cdt_3_can_use_cxx20_format() {

Constrained_triangulation_3/include/CGAL/Constrained_triangulation_3/internal/config.h

@@ -66,7 +66,7 @@ class Epic_converter {
     if(fit_in_double(n,d)){
       return std::make_pair(d,true);
     }
-    return std::make_pair(0,false);
+    return {};
   }
 
   std::pair<Bbox_2,bool> operator()(const Bbox_2 b) const
@@ -86,7 +86,7 @@ class Epic_converter {
     if(fit_in_double(p.x(),x) && fit_in_double(p.y(),y)){
       return std::make_pair(Point_2(x,y),true);
     }
-    return std::make_pair(ORIGIN,false);
+    return {};
   }
 
   std::pair<Vector_2,bool> operator()(const typename IK::Vector_2& v) const
@@ -96,7 +96,7 @@ class Epic_converter {
     if(fit_in_double(v.x(),x) && fit_in_double(v.y(),y)){
       return std::make_pair(Vector_2(x,y),true);
     }
-    return std::make_pair(Vector_2(),false);
+    return {};
   }
 
   std::pair<Direction_2,bool> operator()(const typename IK::Direction_2& d) const
@@ -106,7 +106,7 @@ class Epic_converter {
     if(fit_in_double(d.dx(),x) && fit_in_double(d.dy(),y)){
       return std::make_pair(Direction_2(x,y),true);
     }
-    return std::make_pair(Direction_2(),false);
+    return {};
   }
 
   std::pair<Weighted_point_2,bool> operator()(const typename IK::Weighted_point_2& wp) const
@@ -116,18 +116,18 @@ class Epic_converter {
     if(sp.second && w.second){
       return std::make_pair(Weighted_point_2(sp.first,w.first),true);
     }
-    return std::make_pair(Weighted_point_2(),false);
+    return {};
   }
 
   std::pair<Segment_2,bool> operator()(const typename IK::Segment_2& s) const
   {
     std::pair<Point_2,bool> sp = operator()(s.source());
     if(! sp.second){
-      return std::make_pair(Segment_2(),false);
+      return {};
     }
     std::pair<Point_2,bool> tp = operator()(s.target());
     if(! tp.second){
-      return std::make_pair(Segment_2(),false);
+      return {};
     }
     return std::make_pair(Segment_2(sp.first,tp.first), true);
   }
@@ -138,18 +138,18 @@ class Epic_converter {
     if(a.second && b.second && c.second){
       return std::make_pair(Line_2(a.first, b.first, c.first),true);
     }
-    return std::make_pair(Line_2(), false);
+    return {};
   }
 
   std::pair<Ray_2,bool> operator()(const typename IK::Ray_2& r) const
   {
     std::pair<Point_2,bool> sp = operator()(r.source());
     if(! sp.second){
-      return std::make_pair(Ray_2(),false);
+      return {};
     }
     std::pair<Point_2,bool> tp = operator()(r.second_point());
     if(! tp.second){
-      return std::make_pair(Ray_2(),false);
+      return {};
     }
     return std::make_pair(Ray_2(sp.first,tp.first), true);
   }
@@ -158,15 +158,15 @@ class Epic_converter {
   {
     std::pair<Point_2,bool> v0 = operator()(t.vertex(0));
     if(! v0.second){
-      return std::make_pair(Triangle_2(),false);
+      return {};
     }
     std::pair<Point_2,bool> v1 = operator()(t.vertex(1));
     if(! v1.second){
-      return std::make_pair(Triangle_2(),false);
+      return {};
     }
     std::pair<Point_2,bool> v2 = operator()(t.vertex(2));
     if(! v2.second){
-      return std::make_pair(Triangle_2(),false);
+      return {};
     }
     return std::make_pair(Triangle_2(v0.first,v1.first, v2.first), true);
   }
@@ -178,18 +178,18 @@ class Epic_converter {
     if(c.second && sr.second){
       return std::make_pair(Circle_2(c.first, sr.first, ci.orientation()),true);
     }
-    return std::make_pair(Circle_2(), false);
+    return {};
   }
 
   std::pair<Iso_rectangle_2,bool> operator()(const typename IK::Iso_rectangle_2& ir) const
   {
     std::pair<Point_2,bool> sp = operator()((ir.min)());
     if(! sp.second){
-      return std::make_pair(Iso_rectangle_2(),false);
+      return {};
     }
     std::pair<Point_2,bool> tp = operator()((ir.max)());
     if(! tp.second){
-      return std::make_pair(Iso_rectangle_2(),false);
+      return {};
     }
     return std::make_pair(Iso_rectangle_2(sp.first,tp.first), true);
   }
@@ -199,11 +199,11 @@ class Epic_converter {
   {
     std::pair<Point_3,bool> sp = operator()(li.point());
     if(! sp.second){
-      return std::make_pair(Line_3(),false);
+      return {};
     }
     std::pair<Vector_3,bool> tp = operator()(li.to_vector());
     if(! tp.second){
-      return std::make_pair(Line_3(),false);
+      return {};
     }
     return std::make_pair(Line_3(sp.first,tp.first), true);
   }
@@ -214,22 +214,22 @@ class Epic_converter {
     if(a.second && b.second && c.second && d.second){
       return std::make_pair(Plane_3(a.first, b.first, c.first, d.first),true);
     }
-    return std::make_pair(Plane_3(), false);
+    return {};
   }
 
   std::pair<Triangle_3,bool> operator()(const typename IK::Triangle_3& t) const
   {
     std::pair<Point_3,bool> v0 = operator()(t.vertex(0));
     if(! v0.second){
-      return std::make_pair(Triangle_3(),false);
+      return {};
     }
     std::pair<Point_3,bool> v1 = operator()(t.vertex(1));
     if(! v1.second){
-      return std::make_pair(Triangle_3(),false);
+      return {};
     }
     std::pair<Point_3,bool> v2 = operator()(t.vertex(2));
     if(! v2.second){
-      return std::make_pair(Triangle_3(),false);
+      return {};
     }
     return std::make_pair(Triangle_3(v0.first,v1.first, v2.first), true);
   }
@@ -238,19 +238,19 @@ class Epic_converter {
   {
     std::pair<Point_3,bool> v0 = operator()(t.vertex(0));
     if(! v0.second){
-      return std::make_pair(Tetrahedron_3(),false);
+      return {};
     }
     std::pair<Point_3,bool> v1 = operator()(t.vertex(1));
     if(! v1.second){
-      return std::make_pair(Tetrahedron_3(),false);
+      return {};
     }
     std::pair<Point_3,bool> v2 = operator()(t.vertex(2));
     if(! v2.second){
-      return std::make_pair(Tetrahedron_3(),false);
+      return {};
     }
     std::pair<Point_3,bool> v3 = operator()(t.vertex(3));
     if(! v3.second){
-      return std::make_pair(Tetrahedron_3(),false);
+      return {};
     }
     return std::make_pair(Tetrahedron_3(v0.first,v1.first, v2.first, v3.first), true);
   }
@@ -259,11 +259,11 @@ class Epic_converter {
   {
     std::pair<Point_3,bool> sp = operator()(r.source());
     if(! sp.second){
-      return std::make_pair(Ray_3(),false);
+      return {};
     }
     std::pair<Point_3,bool> tp = operator()(r.second_point());
     if(! tp.second){
-      return std::make_pair(Ray_3(),false);
+      return {};
     }
     return std::make_pair(Ray_3(sp.first,tp.first), true);
   }
@@ -275,7 +275,7 @@ class Epic_converter {
     if(fit_in_double(p.x(),x) && fit_in_double(p.y(),y) && fit_in_double(p.z(),z)){
       return std::make_pair(Point_3(x,y,z),true);
     }
-    return std::make_pair(ORIGIN,false);
+    return {};
   }
 
   std::pair<Vector_3,bool> operator()(const typename IK::Vector_3& v) const
@@ -285,7 +285,7 @@ class Epic_converter {
     if(fit_in_double(v.x(),x) && fit_in_double(v.y(),y) && fit_in_double(v.z(),z)){
       return std::make_pair(Vector_3(x,y,z),true);
     }
-    return std::make_pair(Vector_3(),false);
+    return {};
   }
 
   std::pair<Direction_3,bool> operator()(const typename IK::Direction_3& d) const
@@ -295,18 +295,18 @@ class Epic_converter {
     if(fit_in_double(d.dx(),x) && fit_in_double(d.dy(),y) && fit_in_double(d.dz(),z)){
       return std::make_pair(Direction_3(x,y,z),true);
     }
-    return std::make_pair(Direction_3(),false);
+    return {};
   }
 
   std::pair<Segment_3,bool> operator()(const typename IK::Segment_3& s) const
   {
     std::pair<Point_3,bool> sp = operator()(s.source());
     if(! sp.second){
-      return std::make_pair(Segment_3(),false);
+      return {};
     }
     std::pair<Point_3,bool> tp = operator()(s.target());
     if(! tp.second){
-      return std::make_pair(Segment_3(),false);
+      return {};
     }
     return std::make_pair(Segment_3(sp.first,tp.first), true);
   }
@@ -318,7 +318,7 @@ class Epic_converter {
     if(sp.second && w.second){
       return std::make_pair(Weighted_point_3(sp.first,w.first),true);
     }
-    return std::make_pair(Weighted_point_3(),false);
+    return {};
   }
 
   std::pair<Sphere_3,bool> operator()(const typename IK::Sphere_3& s) const
@@ -328,7 +328,7 @@ class Epic_converter {
     if(c.second && sr.second){
       return std::make_pair(Sphere_3(c.first, sr.first, s.orientation()),true);
     }
-    return std::make_pair(Sphere_3(), false);
+    return {};
   }
 
   std::pair<Circle_3,bool> operator()(const typename IK::Circle_3& ci) const
@@ -338,18 +338,18 @@ class Epic_converter {
     if(c.second && sr.second){
       return std::make_pair(Circle_3(sr.first, c.first),true);
     }
-    return std::make_pair(Circle_3(), false);
+    return {};
   }
 
   std::pair<Iso_cuboid_3,bool> operator()(const typename IK::Iso_cuboid_3& ic) const
   {
     std::pair<Point_3,bool> sp = operator()((ic.min)());
     if(! sp.second){
-      return std::make_pair(Iso_cuboid_3(),false);
+      return {};
     }
     std::pair<Point_3,bool> tp = operator()((ic.max)());
     if(! tp.second){
-      return std::make_pair(Iso_cuboid_3(),false);
+      return {};
     }
     return std::make_pair(Iso_cuboid_3(sp.first,tp.first), true);
   }

Filtered_kernel/include/CGAL/Epic_converter.h

@@ -475,8 +475,8 @@ bool collect_intersections(const std::array<typename K::Point_3, 3>& t1,
 
 //  #warning TODO get rid of sort and unique calls
   // because we don't handle intersection type and can have edge-edge edge-vertex duplicates
-  std::sort(inter_pts.begin(), inter_pts.end(), [](auto p, auto q){return std::get<0>(p)<std::get<0>(q);});
-  auto last = std::unique(inter_pts.begin(), inter_pts.end(), [](auto p, auto q){return std::get<0>(p)==std::get<0>(q);});
+  std::sort(inter_pts.begin(), inter_pts.end(), [](const auto& p, const auto& q){return std::get<0>(p)<std::get<0>(q);});
+  auto last = std::unique(inter_pts.begin(), inter_pts.end(), [](const auto& p, const auto& q){return std::get<0>(p)==std::get<0>(q);});
   inter_pts.erase(last, inter_pts.end());
 
 #ifdef CGAL_AUTOREF_DEBUG_DEPTH

Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/autorefinement.h

@@ -69,12 +69,6 @@ class Prevent_deref
   }
 };
 
-template<typename I>
-Iterator_range<Prevent_deref<I> > make_prevent_deref_range(const Iterator_range<I>& range)
-{
-  return Iterator_range<Prevent_deref<I> >(make_prevent_deref(range.first), make_prevent_deref(range.second));
-}
-
 template<typename I>
 Prevent_deref<I> make_prevent_deref(const I& i)
 {
@@ -87,6 +81,20 @@ Iterator_range<Prevent_deref<I> > make_prevent_deref_range(const I& begin, const
   return Iterator_range<Prevent_deref<I> >(make_prevent_deref(begin), make_prevent_deref(end));
 }
 
+template<typename R>
+auto make_prevent_deref_range(R&& range)
+{
+  static_assert( !std::is_rvalue_reference_v<R&&>,
+                 "make_prevent_deref_range cannot be used with"
+                 " rvalue references to avoid dangling references");
+  // Note: If CGAL were allowed to use C++20, we could use `std::ranges::begin/end`.
+  // That would allow this to work with rvalue ranges when `std::borrowed_range<R>` is `true`.
+  // See https://en.cppreference.com/w/cpp/ranges/begin.html#Notes
+  using std::begin;
+  using std::end;
+  return make_range(make_prevent_deref(begin(range)), make_prevent_deref(end(range)));
+}
+
 namespace cpp98 {
 
 template<typename Category, typename Tp, typename Distance = std::ptrdiff_t,

STL_Extension/include/CGAL/iterator.h

@@ -24,8 +24,6 @@
 #include <CGAL/basic.h>
 
 #include <utility>
-#include <map>
-#include <set>
 #include <vector>
 #include <stack>
 #include <limits>

TDS_3/include/CGAL/Triangulation_data_structure_3.h

@@ -22,6 +22,7 @@
 #include <CGAL/basic.h>
 #include <CGAL/memory.h>
 #include <cstddef>
+#include <iterator>
 
 namespace CGAL {
 
@@ -39,6 +40,7 @@ class UF_forward_iterator {
     typedef R_                                    reference;
     typedef P_                                    pointer;
     typedef std::forward_iterator_tag             iterator_category;
+    typedef std::ptrdiff_t                        difference_type;
 
     UF_forward_iterator() : m_p(0) {}
     UF_forward_iterator(PTR_ p) : m_p(p) {}
@@ -104,6 +106,7 @@ class Union_find {
     typedef T                                                value_type;
     typedef T&                                               reference;
     typedef const T&                                         const_reference;
+    typedef std::forward_iterator_tag                        iterator_category;
 
     typedef internal::UF_forward_iterator< pointer, T, T&, T*>  iterator;
     typedef iterator                                         handle;