patch root to build llvm with c++17

Author: smuzaffar

root-llvm-cxx17.patch

@@ -0,0 +1,40 @@
+diff --git a/interpreter/CMakeLists.txt b/interpreter/CMakeLists.txt
+index de5056d..8f993f7 100644
+--- a/interpreter/CMakeLists.txt
++++ b/interpreter/CMakeLists.txt
+@@ -229,6 +229,11 @@ if(builtin_llvm)
+ 
+   set(LLVM_ENABLE_PROJECTS "clang" CACHE STRING "")
+ 
++  # Always build LLVM with C++17. It is not necessary to compile with the same
++  # C++ standard as the rest of ROOT and sometimes it doesn't even work.
++  set(_cxx_standard ${CMAKE_CXX_STANDARD})
++  set(CMAKE_CXX_STANDARD 17)
++
+   #---Add the sub-directory excluding all the targets from all-----------------------------------------
+   if(CMAKE_GENERATOR MATCHES "Xcode")
+     add_subdirectory(llvm-project/llvm)
+@@ -236,6 +241,8 @@ if(builtin_llvm)
+     add_subdirectory(llvm-project/llvm EXCLUDE_FROM_ALL)
+   endif()
+ 
++   set(CMAKE_CXX_STANDARD ${_cxx_standard})
++
+   set(LLVM_INCLUDE_DIRS ${CMAKE_SOURCE_DIR}/interpreter/llvm-project/llvm/include
+     ${CMAKE_BINARY_DIR}/interpreter/llvm-project/llvm/include
+     CACHE STRING "LLVM include directories."
+@@ -446,7 +453,14 @@ else()
+     # Disable linking against shared LLVM
+     set(LLVM_LINK_LLVM_DYLIB OFF)
+ 
++    # Always build LLVM with C++17. It is not necessary to compile with the same
++    # C++ standard as the rest of ROOT and sometimes it doesn't even work.
++    set(_cxx_standard ${CMAKE_CXX_STANDARD})
++    set(CMAKE_CXX_STANDARD 17)
++
+     add_subdirectory(llvm-project/clang EXCLUDE_FROM_ALL)
++
++    set(CMAKE_CXX_STANDARD ${_cxx_standard})
+   endif(builtin_clang)
+ 
+   set( CLANG_BUILT_STANDALONE 1 )

root.spec

@@ -8,6 +8,7 @@
 
 %define github_user cms-sw
 Source: git+https://github.com/%{github_user}/root.git?obj=%{branch}/%{tag}&export=%{n}-%{realversion}&output=/%{n}-%{realversion}-%{tag}.tgz
+Patch0: root-llvm-cxx17
 
 BuildRequires: cmake ninja
 
@@ -27,6 +28,7 @@ Requires: dcap
 
 %prep
 %setup -n %{n}-%{realversion}
+%patch0 -p1
 %get_config_sub graf2d/asimage/src/libAfterImage/config.sub
 %get_config_guess graf2d/asimage/src/libAfterImage/config.guess
 chmod +x graf2d/asimage/src/libAfterImage/config.{sub,guess}