From 73aa51608e3516c54e712ebe7defb5642261d409 Mon Sep 17 00:00:00 2001
From: Nils Wentzell <nwentzell@flatironinstitute.org>
Date: Mon, 1 Feb 2021 09:42:03 -0500
Subject: [PATCH] [cmake] In extract_flags.cmake inspect
 INTERFACE_COMPILE_FEATURES and add -std=.. flags accordingly

---
 share/cmake/extract_flags.cmake | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/share/cmake/extract_flags.cmake b/share/cmake/extract_flags.cmake
index ed5b6c1f..60e4b453 100644
--- a/share/cmake/extract_flags.cmake
+++ b/share/cmake/extract_flags.cmake
@@ -12,7 +12,7 @@
 #
 # You may obtain a copy of the License at
 #     https://www.gnu.org/licenses/gpl-3.0.txt
-
+# Author: Nils Wentzell
 
 # Recursively fetch all targets that the interface of a target depends upon
 macro(get_all_interface_targets name target)
@@ -59,6 +59,13 @@ macro(extract_flags)
     set(${target}_CXXFLAGS "${${target}_CXXFLAGS} ${opt}")
   endforeach()
 
+  get_property_recursive(cxx_features TARGET ${target} PROPERTY INTERFACE_COMPILE_FEATURES)
+  if(cxx_std_20 IN_LIST cxx_features)
+    set(${target}_CXXFLAGS "${${target}_CXXFLAGS} -std=c++20")
+  elseif(cxx_std_17 IN_LIST cxx_features)
+    set(${target}_CXXFLAGS "${${target}_CXXFLAGS} -std=c++17")
+  endif()
+
   get_property_recursive(defs TARGET ${target} PROPERTY INTERFACE_COMPILE_DEFINITIONS)
   foreach(def ${defs})
     set(${target}_CXXFLAGS "${${target}_CXXFLAGS} -D${def}")