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[cmake] raise warning about soon-obsolete CMake versions #23385

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[cmake] raise warning about soon-obsolete CMake versions #23385

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0bacec1
[cmake] raise warning about soon-obsolete CMake versions
ferdymercury Sep 16, 2026
21d0954
[nfc] mention cmake schedule in RelNotes
ferdymercury Sep 16, 2026
ed18824
[RN] add link to LLVM cmake version discussion
ferdymercury Sep 16, 2026
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12 changes: 12 additions & 0 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,18 @@
# For the list of contributors see $ROOTSYS/README/CREDITS.

cmake_minimum_required(VERSION 3.20 FATAL_ERROR)
if("${CMAKE_VERSION}" VERSION_LESS "3.23.0")
message(WARNING
"Your CMake version is ${CMAKE_VERSION}. Starting with ROOT 6.44, the "
"minimum version of CMake required to build ROOT will become 3.23.0, and "
"using an older CMake will raise an error. After ROOT 6.44, the CMake version "
"is expected to rise to 3.31.0 in sync with LLVM 24.")
elseif("${CMAKE_VERSION}" VERSION_LESS "3.31.0")
message(WARNING
"Your CMake version is ${CMAKE_VERSION}. After ROOT 6.44, the "
"minimum version of CMake required to build ROOT will become 3.31.0, and "
"using an older CMake will raise an error, in sync with LLVM 24.")
endif()

if(WIN32)
# Set CMP0091 (MSVC runtime library flags are selected by an abstraction) to OLD
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5 changes: 5 additions & 0 deletions README/ReleaseNotes/v642/index.md
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Expand Up @@ -86,6 +86,11 @@ The `TMVA_SOFIE_GNN` tutorials have been migrated to this workflow and produce i

## Build System

### CMake version

CMake versions below 3.31 will emit a warning during configure, since they will become obsolete soon: 3.23 will be minimum required in ROOT 6.44 and 3.31 after ROOT 6.44, to gradually stay in sync with the [minimum version of CMake required by LLVM](https://discourse.llvm.org/t/rfc-raising-minimum-required-cmake-version-to-3-31/91086).


### Optimization of ROOT header files

In ROOT 6.22, many (but not all) unused includes were removed from ROOT header files. The remaining unused includes will be removed after ROOT 6.44.
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