Require at least CMake 3.16 and clang-10

The CMake change is now explicit. It was implicitly required by later versions of Kokkos.

clang-9 was failing to build the code for quite a while since it did not compile some proper C++17 code.

CMakeLists.txt

-cmake_minimum_required (VERSION 3.10)
+cmake_minimum_required (VERSION 3.16)
 
 # CMake utils
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
@@ -22,6 +22,9 @@ if("${PUGS_SHORT_VERSION}" STREQUAL "")
   message(FATAL_ERROR "Unable to compute short version from PUGS_VERSION=${PUGS_VERSION}")
 endif()
 
+
+set(CMAKE_CONFIGURATION_TYPES "Release;Debug;Coverage" CACHE STRING INTERNAL FORCE )
+
 # set project version as PUGS_SHORT_VERSION
 project (Pugs VERSION ${PUGS_SHORT_VERSION})
 
@@ -34,16 +37,6 @@ set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 set(PUGS_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
 set(PUGS_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}")
 
-# Change RelWithDebInfo to compile assertions
-SET("CMAKE_CXX_FLAGS_RELWITHDEBINFO"
-   "-g -O2"
-  CACHE STRING "Flags used by the compiler during release builds with debug info and assertions"
-  FORCE )
-SET("CMAKE_C_FLAGS_RELWITHDEBINFO"
-   "-g -O2"
-  CACHE STRING "Flags used by the compiler during release builds with debug info and assertions"
-  FORCE )
-
 # Add new build types
 set(CMAKE_CXX_FLAGS_COVERAGE
   "-g -O0 --coverage"
@@ -68,16 +61,16 @@ mark_as_advanced(
   CMAKE_SHARED_LINKER_FLAGS_COVERAGE )
 
 if(CMAKE_BUILD_TYPE)
-  string(REGEX MATCH "(Debug|Release|RelWithDebInfo|MinSizeRel|Coverage)" VALID_BUILD_TYPE "${CMAKE_BUILD_TYPE}")
+  string(REGEX MATCH "^(Release|Debug|Coverage)$" VALID_BUILD_TYPE "${CMAKE_BUILD_TYPE}")
   if(NOT VALID_BUILD_TYPE)
     message(FATAL_ERROR "Invalid CMAKE_BUILD_TYPE: '${CMAKE_BUILD_TYPE}'")
   endif()
 endif()
 
-# Default build type is RelWIthDebInfo
+# Default build type is Release
 if(NOT CMAKE_BUILD_TYPE)
-  set(CMAKE_BUILD_TYPE "RelWithDebInfo" CACHE STRING
-      "Choose the type of build: Debug Release RelWithDebInfo MinSizeRel Coverage."
+  set(CMAKE_BUILD_TYPE "Release" CACHE STRING
+      "Choose the type of build: Release Debug Coverage."
       FORCE)
 endif()
 
@@ -90,8 +83,8 @@ endif()
 #------------------------------------------------------
 
 # Checks if compiler version is compatible with Pugs sources
-set(GNU_CXX_MIN_VERSION "8.0.0")
-set(CLANG_CXX_MIN_VERSION "8.0.0")
+set(GNU_CXX_MIN_VERSION "9.0.0")
+set(CLANG_CXX_MIN_VERSION "10.0.0")
 
 # Pugs default compiler flags
 set(PUGS_CXX_FLAGS "${PUGS_CXX_FLAGS} -Wall -Wextra -pedantic")
@@ -107,11 +100,11 @@ elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
   set(PUGS_CXX_FLAGS "${PUGS_CXX_FLAGS} -Wsign-compare -Wunused -Wunused-member-function -Wunused-private-field")
 endif()
 
-if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-  if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "9.0.0")
-    set(PUGS_STD_LINK_FLAGS "-lstdc++fs")
-  endif()
-endif()
+# if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+#   if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "9.0.0")
+#     set(PUGS_STD_LINK_FLAGS "-lstdc++fs")
+#   endif()
+# endif()
 
 #------------------------------------------------------
 
@@ -327,12 +320,10 @@ endif()
 # Compiler flags
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${PUGS_CXX_FLAGS}")
 set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} ${PUGS_CXX_FLAGS}")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO} ${PUGS_CXX_FLAGS}")
 
 # Add debug mode for Standard C++ library (not for AppleClang since it is broken)
 if (NOT "${CMAKE_CXX_COMPILER_ID}" STREQUAL "AppleClang")
   set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -D_GLIBCXX_DEBUG -D_LIBCPP_DEBUG=1")
-  set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO} -D_GLIBCXX_DEBUG -D_LIBCPP_DEBUG=1")
 endif()
 
 #------------------------------------------------------
@@ -600,20 +591,29 @@ target_link_libraries(
 include(PugsDoxygen)
 
 # ------------------- Installation --------------------
-# temporary version workaround
-if(${CMAKE_VERSION} VERSION_LESS "3.13.0")
-  install(TARGETS pugs
-    RUNTIME DESTINATION bin
-    LIBRARY DESTINATION lib
-    ARCHIVE DESTINATION lib)
-else()
-  install(TARGETS pugs PugsAlgebra PugsAnalysis PugsUtils PugsLanguage PugsLanguageAST PugsLanguageModules PugsLanguageAlgorithms  PugsLanguageUtils PugsMesh PugsScheme PugsOutput
+install(TARGETS
+  pugs
+  PugsMesh
+  PugsAlgebra
+  PugsAnalysis
+  PugsUtils
+  PugsLanguage
+  PugsLanguageAST
+  PugsLanguageModules
+  PugsLanguageAlgorithms
+  PugsMesh
+  PugsAlgebra
+  PugsScheme
+  PugsUtils
+  PugsOutput
+  PugsLanguageUtils
+  kokkos
 
   RUNTIME DESTINATION bin
   LIBRARY DESTINATION lib
   ARCHIVE DESTINATION lib)
-endif()
 
+# ------------------- Build options -------------------
 message("")
 message("====== pugs build options ======")
 message(" version: ${PUGS_VERSION}")