Headers not found in Geant4 cmake application

[jvavrek]

I’m trying to build a Geant4 application that uses some ROOT classes. It works for ROOT5 but it’s about time I added support for ROOT6.

However, I’m running into a strange issue where the CMakeLists.txt of the Geant code cannot find the ROOT headers:

fatal error: 'TGraph.h' file not found
#include "TGraph.h"

I have edited CMakeLists.txt a bit to print more info:

# Add ROOT?
#
list(APPEND CMAKE_PREFIX_PATH $ENV{ROOTSYS})
find_package(ROOT REQUIRED COMPONENTS RIO)
if (ROOT_FOUND)
  message("ROOT found: ${ROOT_INCLUDE_DIR}")
else()
  message (FATAL_ERROR "ROOT not found")
endif()
include_directories(${ROOT_INCLUDE_DIR})

which produces

(base) jvavrek:~/project$ cmake .
ROOT found: 
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/jvavrek/project

So it looks like cmake is finding the ROOT installation but not the includes in ROOT_INCLUDE_DIR, which is an empty string. If I manually replace ROOT_INCLUDE_DIR with /Users/jvavrek/root/install/include everything compiles. If I put that path on $PATH, but let cmake try to find the libraries, the build fails again.

ROOT Version: ROOT 6.18/00
Platform: Mac OS X 10.14.6
Compiler: cmake version 3.15.4

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[jvavrek]

Aha! It is ROOT_INCLUDE_DIRS with an S at the end, not ROOT_INCLUDE_DIR !