From b209c02fce68389055993f0e60cd9ba316dc9212 Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Thu, 2 Mar 2023 03:26:09 -0700
Subject: [PATCH] Add a check for concepts to the C++20 test.

---
 cmake/checks/check_01_cxx_features.cmake | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/cmake/checks/check_01_cxx_features.cmake b/cmake/checks/check_01_cxx_features.cmake
index e7793e49b0..b6b9a0b28a 100644
--- a/cmake/checks/check_01_cxx_features.cmake
+++ b/cmake/checks/check_01_cxx_features.cmake
@@ -66,6 +66,8 @@ macro(_test_cxx20_support)
   # of the C++20 standard (which will have "202002L" when finalized). gcc-10
   # exports this version number when configured with C++20 support.
   # clang-10 exports the final "202002L" version instead, as does gcc-11.
+  #
+  # Beyond this, check for some features we actually need.
   CHECK_CXX_SOURCE_COMPILES(
     "
     #include <cmath>
@@ -79,6 +81,20 @@ macro(_test_cxx20_support)
     #  error \"insufficient support for C++20\"
     #endif
 
+
+    // Test concepts and requires clauses
+    template <int dim, int spacedim>
+    concept is_valid_dim_spacedim = (dim >= 1 && spacedim <= 3 &&
+                                     dim <= spacedim);
+
+    template <int dim, int spacedim>
+    requires is_valid_dim_spacedim<dim,spacedim>
+    class Triangulation 
+    {};
+
+    Triangulation<1,3> t;
+
+
     int main()
     {
     }
-- 
2.39.5