[core] no longer provide transitive unused includes

README/ReleaseNotes/v642/index.md

@@ -85,6 +85,14 @@ The `TMVA_SOFIE_GNN` tutorials have been migrated to this workflow and produce i
 
 ## Build System
 
+### 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 are now removed in ROOT 6.42.
+For instance, `#include "TBuffer.h"` was removed from `TKey.h`. This change may cause errors during compilation of ROOT-based code if one was implicitly relying on this transitive include on downstream code using TBuffer without actually including `TBuffer.h`. Another example: `TStyle.h` no longer includes internally `TArrayI.h`.
+To fix it in downstream code, provide the missing includes if you were using those classes from transitive includes without explicitly including them.
+This improves compile times and reduces code inter-dependency; see https://github.com/include-what-you-use/include-what-you-use/blob/master/docs/WhyIWYU.md for a good overview of the motivation.
+The macro `R__LESS_INCLUDES` no longer has an effect since it's the new default behavior.
+
 ### Moving from builtin dependencies to system-provided packages
 
 * The general direction of the ROOT project is to become more and more reliant on system packages. It is *recommended* to make the packages required by ROOT available on the system, e.g. via a package manager, and not with the builtin mechanism. This allows for timely updates and reduces the size of the installed binaries.

cmake/modules/RootConfiguration.cmake

@@ -388,11 +388,6 @@ if(dataframe)
 else()
   set(hasdataframe undef)
 endif()
-if(dev)
-  set(use_less_includes define)
-else()
-  set(use_less_includes undef)
-endif()
 if(root7)
   set(hasroot7 define)
 else()

config/RConfigure.in

@@ -51,7 +51,6 @@
 #@hascurl@ R__HAS_CURL  /**/
 #@hasdataframe@ R__HAS_DATAFRAME /**/
 #@hasroot7@ R__HAS_ROOT7 /**/
-#@use_less_includes@ R__LESS_INCLUDES /**/
 #define R__HARDWARE_INTERFERENCE_SIZE @hardwareinterferencesize@ /*Determined at CMake configure to be stable across all TUs*/
 
 #@usezlibng@ R__HAS_ZLIB_NG /**/

core/base/inc/Rtypes.h

@@ -23,13 +23,6 @@
 #include "RtypesCore.h"
 // #include "DllImport.h" // included via RtypesCore.h, not used here
 
-#ifndef R__LESS_INCLUDES
-#include <cstdio>
-#include "strtok.h"     // provides R__STRTOK_R with <cstring> include
-#include "strlcpy.h"    // part of string.h on systems that have it
-#include <type_traits>
-#endif
-
 #include <typeinfo>
 #include <atomic>
 

core/base/inc/TDirectory.h

@@ -26,14 +26,7 @@
 #include "TUUID.h"
 #include <atomic>
 
-#ifdef R__LESS_INCLUDES
 class TList;
-#else
-#include "TList.h"
-#include "TBuffer.h"
-// #include "TDatime.h"
-#endif
-
 class TBrowser;
 class TKey;
 class TFile;

core/base/inc/TFileInfo.h

@@ -23,16 +23,9 @@
 #include "TNamed.h"
 #include "TList.h"
 
-#ifdef R__LESS_INCLUDES
 class TUrl;
 class TUUID;
 class TMD5;
-#else
-#include "TUrl.h"
-#include "TUUID.h"
-#include "TMD5.h"
-#endif
-
 class TFileInfoMeta;
 
 

core/base/inc/TProcessID.h

@@ -24,15 +24,10 @@
 
 #include "TNamed.h"
 
-#ifdef R__LESS_INCLUDES
-class TObjArray;
-#else
-#include "TObjArray.h"
-#endif
-
 #include <atomic>
 #include <type_traits>
 
+class TObjArray;
 class TExMap;
 
 namespace ROOT {

core/base/inc/TStyle.h

@@ -20,10 +20,6 @@
 #include "TAttAxis.h"
 #include "TColor.h"
 
-#ifndef R__LESS_INCLUDES
-#include "TArrayI.h"
-#endif
-
 class TBrowser;
 
 class TStyle : public TNamed, public TAttLine, public TAttFill, public TAttMarker, public TAttText {

core/base/inc/TTask.h

@@ -23,15 +23,9 @@
 
 #include "TNamed.h"
 
-#ifdef R__LESS_INCLUDES
 class TList;
-#else
-#include "TList.h"
-#endif
-
 class TBrowser;
 
-
 class TTask : public TNamed {
 
 protected:

core/base/inc/TVirtualMonitoring.h

@@ -22,14 +22,8 @@
 
 #include "TNamed.h"
 
-#ifdef R__LESS_INCLUDES
 class TList;
 class TMap;
-#else
-#include "TList.h"
-#include "TMap.h"
-#endif
-
 class TFile;
 
 class TVirtualMonitoringWriter : public TNamed {

core/foundation/inc/RtypesCore.h

@@ -38,10 +38,6 @@
 
 #include "DllImport.h"
 
-#ifndef R__LESS_INCLUDES
-#include <cstddef> // size_t, NULL
-#endif
-
 //---- Tag used by rootcling to determine constructor used for I/O.
 
 class TRootIOCtor;

core/gui/inc/TContextMenu.h

@@ -15,12 +15,7 @@
 
 #include "TNamed.h"
 
-#ifdef R__LESS_INCLUDES
 class TContextMenuImp;
-#else
-#include "TContextMenuImp.h"
-#endif
-
 class TMethod;
 class TFunction;
 class TMethodArg;

core/gui/inc/TToggle.h

@@ -36,13 +36,8 @@
 
 #include "TNamed.h"
 
-#ifdef R__LESS_INCLUDES
 class TMethodCall;
 class TMethod;
-#else
-#include "TMethodCall.h"
-#include "TMethod.h"
-#endif
 
 class TToggle: public TNamed {
 

core/meta/inc/TClass.h

@@ -24,16 +24,6 @@
 #include "TString.h"
 #include "TSchemaRule.h"
 
-#ifdef R__LESS_INCLUDES
-class TObjArray;
-#else
-#include "TObjArray.h"
-// Not used in this header file; user code should #include this directly.
-// #include "TObjString.h"
-// #include "ThreadLocalStorage.h"
-// #include <set>
-#endif
-
 #include <cstddef>
 #include <map>
 #include <string>
@@ -42,6 +32,7 @@ class TObjArray;
 #include <vector>
 #include <atomic>
 
+class TObjArray;
 class TBaseClass;
 class TBrowser;
 class TDataMember;

core/meta/inc/TMethodArg.h

@@ -24,12 +24,7 @@
 #include "TDictionary.h"
 #include <string>
 
-#ifdef R__LESS_INCLUDES
 class TDataMember;
-#else
-#include "TDataMember.h"
-#endif
-
 class TFunction;
 class TMethod;
 

core/meta/inc/TProtoClass.h

@@ -20,11 +20,7 @@
 class TClass;
 class TList;
 class TRealData;
-#ifdef R__LESS_INCLUDES
 class TDataMember;
-#else
-#include "TDataMember.h"
-#endif
 
 //////////////////////////////////////////////////////////////////////////
 //                                                                      //

core/meta/inc/TSchemaRuleSet.h

@@ -9,12 +9,7 @@
 #include "TClassRef.h"
 #include <vector>
 
-#ifdef R__LESS_INCLUDES
 class TObjArray;
-#else
-#include "TObjArray.h"
-#endif
-
 
 namespace ROOT {
 

core/thread/inc/TThread.h

@@ -28,12 +28,7 @@
 #include "TTimer.h"
 #include <cstdarg>
 
-#ifdef R__LESS_INCLUDES
 class TCondition;
-#else
-#include "TCondition.h"
-#endif
-
 class TMutex;
 class TThreadImp;
 

geom/geom/inc/TGeoCache.h

@@ -15,13 +15,8 @@
 
 #include "TGeoNode.h"
 
-#ifdef R__LESS_INCLUDES
-struct TGeoStateInfo;
-#else
-#include "TGeoStateInfo.h"
-#endif
-
 // forward declarations
+struct TGeoStateInfo;
 class TGeoManager;
 class TGeoHMatrix;
 

geom/geom/inc/TGeoMaterial.h

@@ -16,14 +16,9 @@
 #include <TAttFill.h>
 #include <TList.h>
 
-#ifdef R__LESS_INCLUDES
+// forward declarations
 class TGeoElement;
 class TGeoElementTable;
-#else
-#include "TGeoElement.h"
-#endif
-
-// forward declarations
 class TGeoExtension;
 class TGDMLMatrix;
 

graf2d/gpad/inc/TControlBar.h

@@ -14,12 +14,8 @@
 
 #include "TControlBarButton.h"
 
-#ifdef R__LESS_INCLUDES
 class TObjArray;
 class TControlBarImp;
-#else
-#include "TControlBarImp.h"
-#endif
 
 class TList;
 

graf2d/gpad/inc/TPaveClass.h

@@ -14,11 +14,7 @@
 
 #include "TPaveLabel.h"
 
-#ifdef R__LESS_INCLUDES
 class TClassTree;
-#else
-#include "TClassTree.h"
-#endif
 
 class TPaveClass : public TPaveLabel {
 

graf2d/graf/inc/TGraphPolar.h

@@ -14,11 +14,7 @@
 
 #include "TGraphErrors.h"
 
-#ifdef R__LESS_INCLUDES
 class TGraphPolargram;
-#else
-#include "TGraphPolargram.h"
-#endif
 
 class TGraphPolar : public TGraphErrors {
 

hist/hist/inc/THStack.h

@@ -24,13 +24,9 @@
 #include "TNamed.h"
 #include "TObjArray.h"
 
-#ifdef R__LESS_INCLUDES
 class TH1;
 class TList;
 class TAxis;
-#else
-#include "TH1.h"
-#endif
 
 #include <limits>
 

hist/hist/inc/TSpline.h

@@ -12,14 +12,10 @@
 #ifndef ROOT_TSpline
 #define ROOT_TSpline
 
-#ifdef R__LESS_INCLUDES
 #include "TNamed.h"
 #include "TAttLine.h"
 #include "TAttFill.h"
 #include "TAttMarker.h"
-#else
-#include "TGraph.h"
-#endif
 
 class TH1;
 class TH1F;

io/io/inc/TFile.h

@@ -31,11 +31,6 @@
 #include "ROOT/RConcurrentHashColl.hxx"
 #include <optional>
 
-// Not a part of TFile interface; provide a forward declaration instead of #include.
-// #ifndef R__LESS_INCLUDES
-// #include "TMap.h"
-// #endif
-
 #ifdef R__USE_IMT
 #include <mutex>
 #endif

io/io/inc/TFilePrefetch.h

@@ -22,13 +22,8 @@
 #include <condition_variable>
 #include <mutex>
 
-#ifdef R__LESS_INCLUDES
 class TSemaphore;
 class TFPBlock;
-#else
-#include "TSemaphore.h"
-#include "TFPBlock.h"
-#endif
 
 class TFilePrefetch : public TObject {
 

io/io/inc/TKey.h

@@ -15,13 +15,9 @@
 #include "TNamed.h"
 #include "TDatime.h"
 #include "TClass.h"
-#ifdef R__LESS_INCLUDES
-class TBuffer;
-#else
-#include "TBuffer.h"
-#endif
 
 class TBrowser;
+class TBuffer;
 class TDirectory;
 class TFile;