[cmake] Make unfold optional so it can be disabled:

It is GPL licensed and ROOT binaries must not have it enabled.

cmake/modules/RootBuildOptions.cmake

@@ -184,6 +184,7 @@ ROOT_BUILD_OPTION(tmva-sofie OFF "Build TMVA with support for sofie - fast infer
 ROOT_BUILD_OPTION(tmva-pymva ON "Enable support for Python in TMVA (requires numpy)")
 ROOT_BUILD_OPTION(tmva-rmva OFF "Enable support for R in TMVA")
 ROOT_BUILD_OPTION(spectrum ON "Enable support for TSpectrum")
+ROOT_BUILD_OPTION(unfold OFF "Enable the unfold package [GPL]")
 ROOT_BUILD_OPTION(unuran OFF "Enable support for UNURAN (package for generating non-uniform random numbers) [GPL]")
 ROOT_BUILD_OPTION(uring OFF "Enable support for io_uring (requires liburing and Linux kernel >= 5.1)")
 ROOT_BUILD_OPTION(vc OFF "Enable support for Vc (SIMD Vector Classes for C++)")
@@ -400,10 +401,15 @@ if(tmva-gpu)
 endif(tmva-gpu)
 
 if(cudnn AND NOT cuda)
-  message(STATUS "Cannot select cudnn without selecting cuda or tmva-gpu. Option is ignored")
+  message(STATUS "Cannot enable cudnn without enabling cuda or tmva-gpu: cudnn is disabled.")
   set(cudnn OFF)
 endif()
 
+if(unfold AND NOT xml)
+  message(STATUS "Cannot enable unfold without enabling xml: unfold is disabled.")
+  set(unfold OFF)
+endif()
+
 if (NOT builtin_cling)
   if (builtin_clang OR builtin_llvm)
     message(WARNING "No need to build internal llvm or clang. Consider turning builtin_clang=Off and builtin_llvm=Off")

hist/CMakeLists.txt

@@ -14,7 +14,7 @@ if (spectrum)
    add_subdirectory(spectrum)
    add_subdirectory(spectrumpainter)  # special CMakeLists.txt
 endif()
-if(xml)
+if(unfold)
   add_subdirectory(unfold)
 endif()
 if(CMAKE_Fortran_COMPILER)

tutorials/CMakeLists.txt

@@ -165,8 +165,11 @@ endif()
 
 if(NOT ROOT_xml_FOUND)
   set(xml_veto  xml/*.C
-                histfactory/*.C    # histfactory requires xml
-                unfold/*.C)        # unfold requires xml
+                histfactory/*.C)   # histfactory requires xml
+endif()
+
+if(NOT ROOT_unfold_FOUND)
+  set(xml_veto  unfold/*.C)
 endif()
 
 if(NOT ROOT_mpi_FOUND)