From 5cb449cd84e062abcdb7714a067265a035dbd1ea Mon Sep 17 00:00:00 2001
From: Matthias Maier <tamiko@43-1.org>
Date: Sun, 24 May 2020 23:27:46 -0500
Subject: [PATCH] CMake: Refactor C++17 bessel function support into separate
 check

---
 cmake/checks/check_01_cxx_features.cmake | 26 +++++++++++++++++++-----
 include/deal.II/base/config.h.in         |  1 +
 include/deal.II/base/std_cxx17/cmath.h   |  4 ++--
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/cmake/checks/check_01_cxx_features.cmake b/cmake/checks/check_01_cxx_features.cmake
index eaa9ab20fa..4682bbb23c 100644
--- a/cmake/checks/check_01_cxx_features.cmake
+++ b/cmake/checks/check_01_cxx_features.cmake
@@ -24,6 +24,7 @@
 #
 #   DEAL_II_HAVE_FP_EXCEPTIONS
 #   DEAL_II_HAVE_COMPLEX_OPERATOR_OVERLOADS
+#   DEAL_II_HAVE_CXX17_BESSEL_FUNCTIONS
 #   DEAL_II_FALLTHROUGH
 #   DEAL_II_DEPRECATED
 #   DEAL_II_CONSTEXPR
@@ -105,10 +106,8 @@ MACRO(_test_cxx17_support)
     DEAL_II_HAVE_CXX17_CONSTEXPR_LAMBDA_BUG_OK
     )
 
-  # Test that the c++17 attributes are supported.
   CHECK_CXX_SOURCE_COMPILES(
     "
-    #include <cmath>
     #include <iostream>
     #include <optional>
     #include <tuple>
@@ -119,9 +118,6 @@ MACRO(_test_cxx17_support)
 
     //check for some C++17 features that we use in our headers:
     using std::apply;
-    using std::cyl_bessel_j;
-    using std::cyl_bessel_jf;
-    using std::cyl_bessel_jl;
     using std::optional;
 
     [[nodiscard]] int test_nodiscard()
@@ -356,6 +352,7 @@ UNSET_IF_CHANGED(CHECK_CXX_FEATURES_FLAGS_SAVED
   DEAL_II_HAVE_COMPLEX_OPERATOR_OVERLOADS
   DEAL_II_HAVE_CXX17_ATTRIBUTE_FALLTHROUGH
   DEAL_II_HAVE_ATTRIBUTE_FALLTHROUGH
+  DEAL_II_HAVE_CXX17_BESSEL_FUNCTIONS
   DEAL_II_CXX14_CONSTEXPR_BUG_OK
   )
 
@@ -551,6 +548,25 @@ ELSE()
 ENDIF()
 
 
+#
+# Check for c++17 bessel function support. Unfortunately libc++ version 10
+# does not have those.
+#
+
+CHECK_CXX_SOURCE_COMPILES(
+  "
+  #include <cmath>
+  using std::cyl_bessel_j;
+  using std::cyl_bessel_jf;
+  using std::cyl_bessel_jl;
+  int main()
+  {
+  }
+  "
+  DEAL_II_HAVE_CXX17_BESSEL_FUNCTIONS
+  )
+
+
 #
 # Check for correct c++14 constexpr support.
 #
diff --git a/include/deal.II/base/config.h.in b/include/deal.II/base/config.h.in
index 836539c207..92b30760aa 100644
--- a/include/deal.II/base/config.h.in
+++ b/include/deal.II/base/config.h.in
@@ -137,6 +137,7 @@
 
 #cmakedefine DEAL_II_HAVE_FP_EXCEPTIONS
 #cmakedefine DEAL_II_HAVE_COMPLEX_OPERATOR_OVERLOADS
+#cmakedefine DEAL_II_HAVE_CXX17_BESSEL_FUNCTIONS
 #cmakedefine DEAL_II_CXX14_CONSTEXPR_BUG
 
 #cmakedefine DEAL_II_DEPRECATED @DEAL_II_DEPRECATED@
diff --git a/include/deal.II/base/std_cxx17/cmath.h b/include/deal.II/base/std_cxx17/cmath.h
index 6695379d2c..bf0f8e93ba 100644
--- a/include/deal.II/base/std_cxx17/cmath.h
+++ b/include/deal.II/base/std_cxx17/cmath.h
@@ -17,7 +17,7 @@
 
 #include <deal.II/base/config.h>
 
-#ifdef DEAL_II_HAVE_CXX17
+#ifdef DEAL_II_HAVE_CXX17_BESSEL_FUNCTIONS
 #  include <cmath>
 #else
 #  include <boost/math/special_functions/bessel.hpp>
@@ -27,7 +27,7 @@
 DEAL_II_NAMESPACE_OPEN
 namespace std_cxx17
 {
-#ifndef DEAL_II_HAVE_CXX17
+#ifndef DEAL_II_HAVE_CXX17_BESSEL_FUNCTIONS
   double (&cyl_bessel_j)(double,
                          double) = boost::math::cyl_bessel_j<double, double>;
   float (&cyl_bessel_jf)(float,
-- 
2.39.5