root-project · ferdymercury · Sep 9, 2026
@@ -40,6 +40,7 @@ The following people have contributed to this new version:
 
 ## Deprecation and Removal
 
+* Starting from ROOT 6.42, the recommended way to include headers is to use e.g `<ROOT/TCanvas.h>` instead of the traditional `"TCanvas.h"`. The traditional variant will stop working in ROOT 7, a point at which you will need to either add that prefix in all your scripts, or alternatively add the extra ROOT/ folder to the global search include paths of your program.
 * The build options `vc`, `veccore`, `builtin_vc`, `builtin_veccore` and `rpath` that were deprecated are now removed and will result in configuration errors if used.
 * The option `fail-on-missing=OFF` is no longer honored for opt-in (ie OFF by default) build options requiring external dependencies such as `arrow`, `cocoa`, `daos`, `daos_mock`, `dcache`, `experimental_adaptivecpp`, `fcgi`, `fortran`, `gviz`, `mpi`, `pythia8`, `qt6web`, `tmva-cudnn`, `tmva-pymva`, `tmva-sofie`, `uring` or `vecgeom`. If the respective associated package dependency is not installed, ROOT will always raise a configuration error independent of the value of `fail-on-missing`. The user has to take action by either providing the dependency or manually disabling that option via `-Darrow=OFF`.
   Note that `all=ON` enables several of these options, so building with `-Dall=ON` now requires all of their dependencies to be installed, or the unwanted ones to be disabled explicitly.

@@ -22,98 +22,98 @@ set(BASE_HEADERS
   ROOT/TExecutorCRTP.hxx
   ROOT/TSequentialExecutor.hxx
   ROOT/StringConv.hxx
-  Buttons.h
-  Bytes.h
-  Byteswap.h
-  KeySymbols.h
-  MessageTypes.h
+  ROOT/Buttons.h
+  ROOT/Bytes.h
+  ROOT/Byteswap.h
+  ROOT/KeySymbols.h
+  ROOT/MessageTypes.h
   Riostream.h
-  Rtypes.h
-  TApplication.h
-  TAtt3D.h
-  TAttAxis.h
-  TAttBBox2D.h
-  TAttBBox.h
-  TAttFill.h
-  TAttLine.h
-  TAttMarker.h
-  TAttPad.h
-  TAttText.h
-  TBase64.h
-  TBenchmark.h
-  TBuffer3D.h
-  TBuffer3DTypes.h
-  TBuffer.h
-  TColor.h
-  TColorGradient.h
-  TDatime.h
-  TDirectory.h
-  TEnv.h
-  TException.h
-  TExec.h
-  TFileCollection.h
-  TFileInfo.h
-  TFolder.h
-  TInetAddress.h
-  TMacro.h
-  TMathBase.h
-  TMD5.h
-  TMemberInspector.h
-  TMessageHandler.h
-  TNamed.h
-  TNotifyLink.h
-  TObject.h
-  TObjString.h
-  TParameter.h
-  TPluginManager.h
-  TPoint.h
-  TPRegexp.h
-  TProcessID.h
-  TProcessUUID.h
-  TQClass.h
-  TQCommand.h
-  TQConnection.h
-  TQObject.h
-  TRedirectOutputGuard.h
-  TRefCnt.h
-  TRef.h
-  TRegexp.h
-  TRemoteObject.h
-  TROOT.h
-  TRootIOCtor.h
-  TStopwatch.h
-  TStorage.h
-  TString.h
-  TStringLong.h
-  TStyle.h
-  TSysEvtHandler.h
-  TSystemDirectory.h
-  TSystemFile.h
-  TSystem.h
-  TTask.h
-  TThreadSlots.h
-  TTime.h
-  TTimer.h
-  TTimeStamp.h
-  TUri.h
-  TUrl.h
-  TUUID.h
-  TVersionCheck.h
-  TVirtualFFT.h
-  TVirtualGL.h
-  TVirtualMonitoring.h
-  TVirtualMapFile.h
-  TVirtualMutex.h
-  TVirtualPadEditor.h
-  TVirtualPad.h
-  TVirtualPadPainter.h
-  TVirtualPerfStats.h
-  TVirtualPS.h
-  TVirtualQConnection.h
-  TVirtualRWMutex.h
-  TVirtualTableInterface.h
-  TVirtualViewer3D.h
-  TVirtualX.h
+  ROOT/Rtypes.h
+  ROOT/TApplication.h
+  ROOT/TAtt3D.h
+  ROOT/TAttAxis.h
+  ROOT/TAttBBox2D.h
+  ROOT/TAttBBox.h
+  ROOT/TAttFill.h
+  ROOT/TAttLine.h
+  ROOT/TAttMarker.h
+  ROOT/TAttPad.h
+  ROOT/TAttText.h
+  ROOT/TBase64.h
+  ROOT/TBenchmark.h
+  ROOT/TBuffer3D.h
+  ROOT/TBuffer3DTypes.h
+  ROOT/TBuffer.h
+  ROOT/TColor.h
+  ROOT/TColorGradient.h
+  ROOT/TDatime.h
+  ROOT/TDirectory.h
+  ROOT/TEnv.h
+  ROOT/TException.h
+  ROOT/TExec.h
+  ROOT/TFileCollection.h
+  ROOT/TFileInfo.h
+  ROOT/TFolder.h
+  ROOT/TInetAddress.h
+  ROOT/TMacro.h
+  ROOT/TMathBase.h
+  ROOT/TMD5.h
+  ROOT/TMemberInspector.h
+  ROOT/TMessageHandler.h
+  ROOT/TNamed.h
+  ROOT/TNotifyLink.h
+  ROOT/TObject.h
+  ROOT/TObjString.h
+  ROOT/TParameter.h
+  ROOT/TPluginManager.h
+  ROOT/TPoint.h
+  ROOT/TPRegexp.h
+  ROOT/TProcessID.h
+  ROOT/TProcessUUID.h
+  ROOT/TQClass.h
+  ROOT/TQCommand.h
+  ROOT/TQConnection.h
+  ROOT/TQObject.h
+  ROOT/TRedirectOutputGuard.h
+  ROOT/TRefCnt.h
+  ROOT/TRef.h
+  ROOT/TRegexp.h
+  ROOT/TRemoteObject.h
+  ROOT/TROOT.h
+  ROOT/TRootIOCtor.h
+  ROOT/TStopwatch.h
+  ROOT/TStorage.h
+  ROOT/TString.h
+  ROOT/TStringLong.h
+  ROOT/TStyle.h
+  ROOT/TSysEvtHandler.h
+  ROOT/TSystemDirectory.h
+  ROOT/TSystemFile.h
+  ROOT/TSystem.h
+  ROOT/TTask.h
+  ROOT/TThreadSlots.h
+  ROOT/TTime.h
+  ROOT/TTimer.h
+  ROOT/TTimeStamp.h
+  ROOT/TUri.h
+  ROOT/TUrl.h
+  ROOT/TUUID.h
+  ROOT/TVersionCheck.h
+  ROOT/TVirtualFFT.h
+  ROOT/TVirtualGL.h
+  ROOT/TVirtualMonitoring.h
+  ROOT/TVirtualMapFile.h
+  ROOT/TVirtualMutex.h
+  ROOT/TVirtualPadEditor.h
+  ROOT/TVirtualPad.h
+  ROOT/TVirtualPadPainter.h
+  ROOT/TVirtualPerfStats.h
+  ROOT/TVirtualPS.h
+  ROOT/TVirtualQConnection.h
+  ROOT/TVirtualRWMutex.h
+  ROOT/TVirtualTableInterface.h
+  ROOT/TVirtualViewer3D.h
+  ROOT/TVirtualX.h
 )
 
 set(BASE_SOURCES
@@ -222,6 +222,7 @@ endif()
 
 target_include_directories(Core PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc>
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc/ROOT> # bw compatibility
 )
 target_include_directories(Core PRIVATE ${CMAKE_SOURCE_DIR}/core/utils/inc)
 

@@ -17,6 +17,7 @@ set_property(TARGET Core APPEND PROPERTY DICT_HEADERS
 
 target_include_directories(Core PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc>
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc/ROOT> # bw compatibility
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/res>
 )
 
@@ -35,10 +36,15 @@ target_include_directories(ClingUtils PRIVATE
    ${CLING_INCLUDE_DIRS}
    ${CMAKE_SOURCE_DIR}/core/foundation/res
    ${CMAKE_SOURCE_DIR}/core/foundation/inc
+   ${CMAKE_SOURCE_DIR}/core/foundation/inc/ROOT # bw compatibility
    ${CMAKE_SOURCE_DIR}/core/base/inc
+   ${CMAKE_SOURCE_DIR}/core/base/inc/ROOT # bw compatibility
    ${CMAKE_SOURCE_DIR}/core/clib/inc
    ${CMAKE_SOURCE_DIR}/core/meta/inc
-   ${CMAKE_BINARY_DIR}/ginclude)
+   ${CMAKE_SOURCE_DIR}/core/meta/inc/ROOT # bw compatibility
+   ${CMAKE_BINARY_DIR}/ginclude
+   ${CMAKE_BINARY_DIR}/ginclude/ROOT # bw compatibility
+   )
 
 # Register the llvm include directories after clangs. This instructs the compiler to resolve
 # headers from our builtin clang. That's an issue when we are building with bultin_llvm=Off

@@ -10,34 +10,34 @@
 
 set_property(TARGET Core APPEND PROPERTY DICT_HEADERS
   ROOT/TSeq.hxx
-  TArrayC.h
-  TArrayD.h
-  TArrayF.h
-  TArray.h
-  TArrayI.h
-  TArrayL64.h
-  TArrayL.h
-  TArrayS.h
-  TBits.h
-  TBtree.h
-  TClassTable.h
-  TClonesArray.h
-  TCollection.h
-  TCollectionProxyInfo.h
-  TExMap.h
-  THashList.h
-  THashTable.h
-  TIterator.h
-  TList.h
-  TMap.h
-  TObjArray.h
-  TObjectTable.h
-  TOrdCollection.h
-  TRefArray.h
-  TRefTable.h
-  TSeqCollection.h
-  TSortedList.h
-  TVirtualCollectionProxy.h
+  ROOT/TArrayC.h
+  ROOT/TArrayD.h
+  ROOT/TArrayF.h
+  ROOT/TArray.h
+  ROOT/TArrayI.h
+  ROOT/TArrayL64.h
+  ROOT/TArrayL.h
+  ROOT/TArrayS.h
+  ROOT/TBits.h
+  ROOT/TBtree.h
+  ROOT/TClassTable.h
+  ROOT/TClonesArray.h
+  ROOT/TCollection.h
+  ROOT/TCollectionProxyInfo.h
+  ROOT/TExMap.h
+  ROOT/THashList.h
+  ROOT/THashTable.h
+  ROOT/TIterator.h
+  ROOT/TList.h
+  ROOT/TMap.h
+  ROOT/TObjArray.h
+  ROOT/TObjectTable.h
+  ROOT/TOrdCollection.h
+  ROOT/TRefArray.h
+  ROOT/TRefTable.h
+  ROOT/TSeqCollection.h
+  ROOT/TSortedList.h
+  ROOT/TVirtualCollectionProxy.h
 )
 
 target_sources(Core PRIVATE
@@ -70,7 +70,8 @@ target_sources(Core PRIVATE
 )
 
 target_include_directories(Core
-  PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc>)
+  PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc>
+  PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc/ROOT>) # bw compatibility
 
 ROOT_INSTALL_HEADERS()
 

@@ -48,9 +48,12 @@ target_include_directories(Dictgen PRIVATE
   ${CMAKE_SOURCE_DIR}/core/foundation/res
   ${CMAKE_SOURCE_DIR}/core/clingutils/res
   ${CMAKE_SOURCE_DIR}/core/base/inc
+  ${CMAKE_SOURCE_DIR}/core/base/inc/ROOT # bw compatibility
   ${CMAKE_SOURCE_DIR}/core/clib/inc
   ${CMAKE_SOURCE_DIR}/core/meta/inc
+  ${CMAKE_SOURCE_DIR}/core/meta/inc/ROOT # bw compatibility
   ${CMAKE_SOURCE_DIR}/core/foundation/inc
+  ${CMAKE_SOURCE_DIR}/core/foundation/inc/ROOT # bw compatibility
   ${CMAKE_BINARY_DIR}/ginclude
   ${CLING_INCLUDE_DIRS}
 )

@@ -9,9 +9,9 @@
 ############################################################################
 
 set_property(TARGET Core APPEND PROPERTY DICT_HEADERS
-  ESTLType.h
-  TClassEdit.h
-  TError.h
+  ROOT/ESTLType.h
+  ROOT/TClassEdit.h
+  ROOT/TError.h
   ThreadLocalStorage.h
   ROOT/BitUtils.hxx
   ROOT/RError.hxx
@@ -20,6 +20,7 @@ set_property(TARGET Core APPEND PROPERTY DICT_HEADERS
   ROOT/RRangeCast.hxx
   ROOT/RSpan.hxx
   ROOT/RStringView.hxx
+  ROOT/RtypesCore.h
   ROOT/StringUtils.hxx
   ROOT/span.hxx
   ROOT/TypeTraits.hxx
@@ -35,13 +36,16 @@ set(FOUNDATION_SOURCES
   src/TError.cxx
 )
 
-set(FOUNDATION_HEADER_DIRS inc/)
+set(FOUNDATION_HEADER_DIRS inc/
+inc/ROOT/ # bw compatibility
+)
 
 target_sources(Core PRIVATE ${FOUNDATION_SOURCES})
 
 target_include_directories(Core
   PUBLIC
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc/ROOT> # bw compatibility
   PRIVATE
     res
 )
@@ -51,6 +55,7 @@ ROOT_OBJECT_LIBRARY(Foundation_Stage1 ${FOUNDATION_SOURCES}) # used by rootcling
 target_include_directories(Foundation_Stage1
   PUBLIC
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc/ROOT> # bw compatibility
   PRIVATE
     $<$<BOOL:${MSVC}>:${CMAKE_SOURCE_DIR}/core/winnt/inc>
     ${CMAKE_BINARY_DIR}/ginclude res