[cmake] raise min required version to 3.26

CMakeLists.txt

@@ -4,14 +4,8 @@
 # For the licensing terms see $ROOTSYS/LICENSE.
 # For the list of contributors see $ROOTSYS/README/CREDITS.
 
-cmake_minimum_required(VERSION 3.20 FATAL_ERROR)
-if("${CMAKE_VERSION}" VERSION_LESS "3.26.0")
-  message(WARNING
-    "Your CMake version is ${CMAKE_VERSION}. Starting with ROOT 6.44, the "
-    "minimum version of CMake required to build ROOT will become 3.26.0, and "
-    "using an older CMake will raise an error. After ROOT 6.44, the CMake version "
-    "may rise to 3.31.0 if an upgrade to LLVM 24 or later is performed.")
-elseif("${CMAKE_VERSION}" VERSION_LESS "3.31.0")
+cmake_minimum_required(VERSION 3.26 FATAL_ERROR)
+if("${CMAKE_VERSION}" VERSION_LESS "3.31.0")
   message(STATUS
     "Your CMake version is ${CMAKE_VERSION}. After ROOT 6.44, the "
     "minimum version of CMake required to build ROOT may become 3.31.0 if "
@@ -56,6 +50,13 @@ foreach(policy ${policy_new})
   endif()
 endforeach()
 
+set(policy_old CMP0126)
+foreach(policy ${policy_old})
+  if(POLICY ${policy})
+    cmake_policy(SET ${policy} OLD)
+  endif()
+endforeach()
+
 include(cmake/modules/CaptureCommandLine.cmake)
 
 project(ROOT)

README/ReleaseNotes/v644/index.md

@@ -12,13 +12,19 @@ For more information, see:
 
 The following people have contributed to this new version:
 
-
 ## Deprecation and Removal
 
 * `TClassEdit::ESTLType`, `TDictionary::ESTLType`, `TStreamerElement::ESTLType` were redundant enums and have been removed. Please use `ROOT::ESTLType` instead.
 * The `ROOT.SetHeuristicMemoryPolicy` method has been removed. This was introduced in 6.40 as a temporary debugging tool to aid users in addressing the changes in memory ownership heuristics.
 * A `RooArgSet` cannot be constructed with an implicit conversion from Python `set` anymore.
 
+## Build system
+
+### CMake version
+
+As announced in the 6.42 release notes, the minimum CMake version required for building ROOT 6.44 rose to 3.26. It is the version shipped with RHEL 8.10, which is the oldest Linux distribution supported by this release.
+After ROOT 6.44, the minimum may rise to 3.31 if an upgrade to LLVM 24 or later is performed, see the [minimum version of CMake required by LLVM](https://discourse.llvm.org/t/rfc-raising-minimum-required-cmake-version-to-3-31/91086), a warning will be emitted at configure time if your CMake version is older than this.
+
 ## Python Interface
 
 ## I/O

cmake/modules/SearchInstalledSoftware.cmake

@@ -1103,13 +1103,6 @@ if (testing OR testsupport)
       message(SEND_ERROR "Missing installation of GTest subcomponent ${LIBNAME}")
     endif()
   endforeach()
-  # Starting from cmake 3.23, the GTest targets will have stable names.
-  # ROOT was updated to use those, but for older CMake versions, we have to declare the aliases:
-  foreach(LIBNAME gtest_main gmock_main gtest gmock)
-    if(NOT TARGET GTest::${LIBNAME} AND TARGET ${LIBNAME})
-      add_library(GTest::${LIBNAME} ALIAS ${LIBNAME})
-    endif()
-  endforeach()
 endif()
 
 #------------------------------------------------------------------------------------

core/base/CMakeLists.txt

@@ -206,18 +206,16 @@ set_property(TARGET Core APPEND PROPERTY DICT_HEADERS ${BASE_HEADERS})
 
 target_sources(Core PRIVATE ${BASE_SOURCES})
 
-if(NOT CMAKE_VERSION VERSION_LESS "3.23.0") # https://discourse.cmake.org/t/file-set-xyz-is-listed-in-interface-file-sets-of-w-but-has-not-been-exported/9131/3
-  target_sources(
-      Core
-      PRIVATE
-      FILE_SET private_header_files
-      TYPE HEADERS
-      BASE_DIRS inc/ src/
-      FILES
-          ${RELATIVE_BASE_INC_HEADERS}
-          src/TListOfTypes.h
-  )
-endif()
+target_sources(
+    Core
+    PRIVATE
+    FILE_SET private_header_files
+    TYPE HEADERS
+    BASE_DIRS inc/ src/
+    FILES
+        ${RELATIVE_BASE_INC_HEADERS}
+        src/TListOfTypes.h
+)
 
 target_include_directories(Core PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc>

roofit/batchcompute/CMakeLists.txt

@@ -117,30 +117,28 @@ set(shared_object_sources src/RooBatchCompute.cxx src/ComputeFunctions.cxx)
 ROOT_LINKER_LIBRARY(RooBatchCompute_GENERIC ${shared_object_sources} TYPE SHARED DEPENDENCIES RooBatchCompute)
 target_compile_options(RooBatchCompute_GENERIC  PRIVATE ${common-flags} -DRF_ARCH=GENERIC)
 
-if(NOT CMAKE_VERSION VERSION_LESS "3.23.0")
-  target_sources(
-      RooBatchCompute
+target_sources(
+    RooBatchCompute
+    PRIVATE
+    FILE_SET private_header_files
+    TYPE HEADERS
+    BASE_DIRS res/
+    FILES
+        res/RooBatchCompute.h
+)
+target_sources(
+      RooBatchCompute_GENERIC
       PRIVATE
       FILE_SET private_header_files
       TYPE HEADERS
-      BASE_DIRS res/
+      BASE_DIRS src/ res/
       FILES
-          res/RooBatchCompute.h
-  )
-  target_sources(
-        RooBatchCompute_GENERIC
-        PRIVATE
-        FILE_SET private_header_files
-        TYPE HEADERS
-        BASE_DIRS src/ res/
-        FILES
-            res/RooBatchComputeTypes.h
-            res/RooHeterogeneousMath.h
-            res/RooNaNPacker.h
-            src/Batches.h
-            src/RooVDTHeaders.h
-  )
-endif()
+          res/RooBatchComputeTypes.h
+          res/RooHeterogeneousMath.h
+          res/RooNaNPacker.h
+          src/Batches.h
+          src/RooVDTHeaders.h
+)
 
 # Windows platform and ICC compiler need special code and testing, thus the feature has not been implemented yet for these.
 if (ROOT_PLATFORM MATCHES "linux|macosx" AND CMAKE_SYSTEM_PROCESSOR MATCHES x86_64 AND CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
@@ -190,17 +188,15 @@ if (cuda)
   endif()
 
   target_compile_options(RooBatchCompute_CUDA  PRIVATE -lineinfo --expt-relaxed-constexpr)
-  if(NOT CMAKE_VERSION VERSION_LESS "3.23.0")
-    target_sources(
-        RooBatchCompute_CUDA
-        PRIVATE
-        FILE_SET private_header_files
-        TYPE HEADERS
-        BASE_DIRS src/
-        FILES
-            src/CudaInterface.h
-    )
-  endif()
+  target_sources(
+      RooBatchCompute_CUDA
+      PRIVATE
+      FILE_SET private_header_files
+      TYPE HEADERS
+      BASE_DIRS src/
+      FILES
+          src/CudaInterface.h
+  )
 endif()
 
 if(vdt OR builtin_vdt)

roofit/codegen/CMakeLists.txt

@@ -22,17 +22,15 @@ ROOT_STANDARD_LIBRARY_PACKAGE(RooFitCodegen
     HistFactory
 )
 
-if(NOT CMAKE_VERSION VERSION_LESS "3.23.0")
-  target_sources(
-      RooFitCodegen
-      PRIVATE
-      FILE_SET private_header_files
-      TYPE HEADERS
-      BASE_DIRS inc/
-      FILES
-          # LinkDef.h # empty, not being used by ROOT_STANDARD_LIBRARY_PACKAGE call
-          inc/RooFit/CodegenImpl.h
-  )
-endif()
+target_sources(
+    RooFitCodegen
+    PRIVATE
+    FILE_SET private_header_files
+    TYPE HEADERS
+    BASE_DIRS inc/
+    FILES
+        # LinkDef.h # empty, not being used by ROOT_STANDARD_LIBRARY_PACKAGE call
+        inc/RooFit/CodegenImpl.h
+)
 
 ROOT_ADD_TEST_SUBDIRECTORY(test)

roofit/histfactory/CMakeLists.txt

@@ -99,18 +99,16 @@ install(FILES ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/${prepareHistFactory_script}
 
 set(RELATIVE_INC_HEADERS ${HISTFACTORY_HEADERS} ${HISTFACTORY_XML_HEADERS})
 list(TRANSFORM RELATIVE_INC_HEADERS PREPEND inc/)
-if(NOT CMAKE_VERSION VERSION_LESS "3.23.0")
-  target_sources(
-      HistFactory
-      PRIVATE
-      FILE_SET private_header_files
-      TYPE HEADERS
-      BASE_DIRS inc/
-      FILES
-          ${RELATIVE_INC_HEADERS}
-          inc/LinkDef.h # seemingly not being used by ROOT_STANDARD_LIBRARY_PACKAGE call
-          inc/HFMsgService.h # not part of list above
-  )
-endif()
+target_sources(
+    HistFactory
+    PRIVATE
+    FILE_SET private_header_files
+    TYPE HEADERS
+    BASE_DIRS inc/
+    FILES
+        ${RELATIVE_INC_HEADERS}
+        inc/LinkDef.h # seemingly not being used by ROOT_STANDARD_LIBRARY_PACKAGE call
+        inc/HFMsgService.h # not part of list above
+)
 
 ROOT_ADD_TEST_SUBDIRECTORY(test)

roofit/hs3/CMakeLists.txt

@@ -39,20 +39,18 @@ target_link_libraries(RooFitHS3 PRIVATE nlohmann_json::nlohmann_json)
 
 set(RELATIVE_INC_HEADERS ${ROOFITHS3_HEADERS})
 list(TRANSFORM RELATIVE_INC_HEADERS PREPEND inc/)
-if(NOT CMAKE_VERSION VERSION_LESS "3.23.0")
-  target_sources(
-      RooFitHS3
-      PRIVATE
-      FILE_SET private_header_files
-      TYPE HEADERS
-      BASE_DIRS inc/ src/
-      FILES
-          ${RELATIVE_INC_HEADERS}
-          # LinkDef.h # seemingly not being used by ROOT_STANDARD_LIBRARY_PACKAGE call
-          src/Domains.h
-          src/JSONIOUtils.h
-          src/static_execute.h
-  )
-endif()
+target_sources(
+    RooFitHS3
+    PRIVATE
+    FILE_SET private_header_files
+    TYPE HEADERS
+    BASE_DIRS inc/ src/
+    FILES
+        ${RELATIVE_INC_HEADERS}
+        # LinkDef.h # seemingly not being used by ROOT_STANDARD_LIBRARY_PACKAGE call
+        src/Domains.h
+        src/JSONIOUtils.h
+        src/static_execute.h
+)
 
 ROOT_ADD_TEST_SUBDIRECTORY(test)

roofit/multiprocess/CMakeLists.txt

@@ -29,33 +29,31 @@ target_include_directories(RooFitMultiProcess
 
 target_link_libraries(RooFitMultiProcess PRIVATE nlohmann_json::nlohmann_json)
 
-if(NOT CMAKE_VERSION VERSION_LESS "3.23.0")
-  target_sources(
-      RooFitMultiProcess
-      PRIVATE
-      FILE_SET private_header_files
-      TYPE HEADERS
-      BASE_DIRS inc/ res/ src/
-      FILES
-        inc/RooFit/MultiProcess/Config.h
-        inc/RooFit/MultiProcess/HeatmapAnalyzer.h
-        inc/RooFit/MultiProcess/types.h
-        res/RooFit/MultiProcess/Channel.h
-        res/RooFit/MultiProcess/JobManager.h
-        res/RooFit/MultiProcess/Job.h
-        res/RooFit/MultiProcess/Message.h
-        res/RooFit/MultiProcess/Messenger.h
-        res/RooFit/MultiProcess/Messenger_decl.h
-        res/RooFit/MultiProcess/Poller.h
-        res/RooFit/MultiProcess/ProcessManager.h
-        res/RooFit/MultiProcess/ProcessTimer.h
-        res/RooFit/MultiProcess/Queue.h
-        res/RooFit/MultiProcess/util.h
-        res/RooFit/MultiProcess/worker.h
-        src/FIFOQueue.h
-        src/PriorityQueue.h
-  )
-endif()
+target_sources(
+    RooFitMultiProcess
+    PRIVATE
+    FILE_SET private_header_files
+    TYPE HEADERS
+    BASE_DIRS inc/ res/ src/
+    FILES
+      inc/RooFit/MultiProcess/Config.h
+      inc/RooFit/MultiProcess/HeatmapAnalyzer.h
+      inc/RooFit/MultiProcess/types.h
+      res/RooFit/MultiProcess/Channel.h
+      res/RooFit/MultiProcess/JobManager.h
+      res/RooFit/MultiProcess/Job.h
+      res/RooFit/MultiProcess/Message.h
+      res/RooFit/MultiProcess/Messenger.h
+      res/RooFit/MultiProcess/Messenger_decl.h
+      res/RooFit/MultiProcess/Poller.h
+      res/RooFit/MultiProcess/ProcessManager.h
+      res/RooFit/MultiProcess/ProcessTimer.h
+      res/RooFit/MultiProcess/Queue.h
+      res/RooFit/MultiProcess/util.h
+      res/RooFit/MultiProcess/worker.h
+      src/FIFOQueue.h
+      src/PriorityQueue.h
+)
 
 ROOT_ADD_TEST_SUBDIRECTORY(test)
 

roofit/roofit/CMakeLists.txt

@@ -175,18 +175,16 @@ endif()
 
 set(RELATIVE_INC_HEADERS ${ROOFIT_HEADERS})
 list(TRANSFORM RELATIVE_INC_HEADERS PREPEND inc/)
-if(NOT CMAKE_VERSION VERSION_LESS "3.23.0")
-  target_sources(
-      RooFit
-      PRIVATE
-      FILE_SET private_header_files
-      TYPE HEADERS
-      BASE_DIRS inc/ src/
-      FILES
-          ${RELATIVE_INC_HEADERS}
-          inc/LinkDef1.h
-          src/RooFit/Detail/Algorithms.h
-  )
-endif()
+target_sources(
+    RooFit
+    PRIVATE
+    FILE_SET private_header_files
+    TYPE HEADERS
+    BASE_DIRS inc/ src/
+    FILES
+        ${RELATIVE_INC_HEADERS}
+        inc/LinkDef1.h
+        src/RooFit/Detail/Algorithms.h
+)
 
 ROOT_ADD_TEST_SUBDIRECTORY(test)