Applications compiled on MacOS with -Wshadow report warnings from 14 ROOT headers

[kelseymh]

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Description

As reported in the ROOT forums in 2019, https://root-forum.cern.ch/t/shadow-warnings-when-compiling-against-root, when a user application is compiled against ROOT on MacOS (reported under 10.15.7/Catalina, still present with Tahoe 26.2), there are fourteen ROOT files which generate compiler warnings via -Wshadow, because they define local enumerator names which duplicate global namespace enums. For example:

<ROOTSYS>/include/root/TBranch.h:108:7: warning: declaration shadows a variable in the global namespace [-Wshadow]
  108 |       kBranchAny    = ::kBranchAny,    ///< Branch is an object*
      |       ^
<ROOTSYS>/include/root/TBranch.h:59:13: note: previous declaration is here
   59 | const Int_t kBranchAny    = BIT(17); // branch is an object*
      |             ^

Following the guidance from @pcanal in that post, I was able to suppress the warnings (but not fix the underlying potential conflict) by adding #pragma directives at the top and bottom of the affected files:

core/base/inc/TApplication.h
core/base/inc/TAttMarker.h
core/base/inc/TSystem.h
core/base/inc/TVirtualX.h
core/meta/inc/TClass.h
core/meta/inc/TInterpreter.h
gui/gui/inc/TGFrame.h
io/io/inc/TFile.h
math/matrix/inc/TMatrixT.h
math/matrix/inc/TMatrixTSparse.h
math/matrix/inc/TMatrixTSym.h
net/net/inc/TSocket.h
tree/tree/inc/TBranch.h

I have copied over from Forums user vaubee a minimal example to demonstrate the problem using TBranch.h.

Reproducer

#include
#include "TROOT.h"
#include "TBranch.h"

int main(int, char**) {
std::cout<<TROOT::GetMacroPath()<<std::endl;
return 0;
}

Comple this on MacOS with clang++ -o test test.cc $(root-config --cflags --libs) -Wshadow

ROOT version

All ROOT versions since at least 6.12/06. Reproduced most recently with 6.36.06.

Installation method

Homebrew (brew install root)

Operating system

MacOS Catalina through Tahoe

Additional context

No response

[aryansri05]

I have opened PR #20793 which implements the suggested fix for these files.

[dpiparo]

@kelseymh thanks for taking the time to report this issue.

[ferdymercury]

Thanks. Note that this is a general problem, not just for Wshadow on MacOS or clang.

For example, I have an application where I turn many other flag warnings. So I ended up using a custom CMake target when generating the dictionaries to avoid this:

ROOT_GENERATE_DICTIONARY(G__PulseSurfer ${CMAKE_CURRENT_SOURCE_DIR}/PulseSurfer.hpp)

add_custom_command(
  OUTPUT suppressWarnings3
  # https://unix.stackexchange.com/questions/43119/preserve-modified-time-stamp-after-edit
  COMMAND cp -p G__PulseSurfer.cxx G__PulseSurfer_.cxx
  COMMAND sed -i '1i_Pragma\(\"GCC diagnostic ignored \\\\\"-Weffc++\\\\\"\"\) _Pragma\(\"GCC diagnostic ignored \\\\\"-Wmissing-declarations\\\\\"\"\)' G__PulseSurfer.cxx
  COMMAND echo '_Pragma\(\"GCC diagnostic warning \\\\\"-Weffc++\\\\\"\"\) _Pragma\(\"GCC diagnostic warning \\\\\"-Wmissing-declarations\\\\\"\"\)' >> G__PulseSurfer.cxx
  #https://unix.stackexchange.com/questions/20573/sed-insert-text-after-the-last-line
  COMMAND touch -r G__PulseSurfer_.cxx G__PulseSurfer.cxx
  DEPENDS G__PulseSurfer.cxx
  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
)

add_library(mygui SHARED G__PulseSurfer.cxx suppressWarnings suppressWarnings3)

Full example: #8365 in the section "To Reproduce"