From fa6afe73d19ede468d43616810ca255326913cbe Mon Sep 17 00:00:00 2001
From: Laurent Rineau <laurent.rineau@cgal.org>
Date: Thu, 21 Jan 2021 11:18:27 +0100
Subject: [PATCH 1/2] Add a static assert so that Parallel_tag can only be used
 with TBB

---
 TDS_3/include/CGAL/Triangulation_data_structure_3.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/TDS_3/include/CGAL/Triangulation_data_structure_3.h b/TDS_3/include/CGAL/Triangulation_data_structure_3.h
index 7c01149ab44..65e94bad71b 100644
--- a/TDS_3/include/CGAL/Triangulation_data_structure_3.h
+++ b/TDS_3/include/CGAL/Triangulation_data_structure_3.h
@@ -56,6 +56,7 @@
 #endif
 
 #include <boost/type_traits/is_convertible.hpp>
+#include <type_traits>
 
 namespace CGAL {
 
@@ -130,6 +131,10 @@ public:
   >::type                                                Cell_range;
 
 # else
+  CGAL_static_assertion_msg
+    (!(std::is_convertible<Concurrency_tag, Parallel_tag>::value),
+     "In CGAL triangulations, `Parallel_tag` can only be used with the Intel TBB library. "
+     "Make TBB available in the build system and then define the macro `CGAL_LINKED_WITH_TBB`.");
   typedef Compact_container<Cell>                        Cell_range;
 #endif
 

From 8e316f63f7dae9ee7dc15eed13b88b0dc7237a54 Mon Sep 17 00:00:00 2001
From: Laurent Rineau <laurent.rineau@cgal.org>
Date: Thu, 21 Jan 2021 11:19:16 +0100
Subject: [PATCH 2/2] Replace <boost/type_traits/is_convertible.hpp> by
 <type_traits>

---
 TDS_3/include/CGAL/Triangulation_data_structure_3.h | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/TDS_3/include/CGAL/Triangulation_data_structure_3.h b/TDS_3/include/CGAL/Triangulation_data_structure_3.h
index 65e94bad71b..2fa274adadc 100644
--- a/TDS_3/include/CGAL/Triangulation_data_structure_3.h
+++ b/TDS_3/include/CGAL/Triangulation_data_structure_3.h
@@ -55,7 +55,6 @@
 #  include <tbb/scalable_allocator.h>
 #endif
 
-#include <boost/type_traits/is_convertible.hpp>
 #include <type_traits>
 
 namespace CGAL {
@@ -123,9 +122,9 @@ public:
   // Cells
   // N.B.: Concurrent_compact_container requires TBB
 #ifdef CGAL_LINKED_WITH_TBB
-  typedef typename boost::mpl::if_c
+  typedef typename std::conditional
   <
-    boost::is_convertible<Concurrency_tag, Parallel_tag>::value,
+    std::is_convertible<Concurrency_tag, Parallel_tag>::value,
     Concurrent_compact_container<Cell, tbb::scalable_allocator<Cell> >,
     Compact_container<Cell>
   >::type                                                Cell_range;
@@ -141,9 +140,9 @@ public:
   // Vertices
   // N.B.: Concurrent_compact_container requires TBB
 #ifdef CGAL_LINKED_WITH_TBB
-  typedef typename boost::mpl::if_c
+  typedef typename std::conditional
   <
-    boost::is_convertible<Concurrency_tag, Parallel_tag>::value,
+    std::is_convertible<Concurrency_tag, Parallel_tag>::value,
     Concurrent_compact_container<Vertex, tbb::scalable_allocator<Vertex> >,
     Compact_container<Vertex>
   >::type                                                Vertex_range;