Can't build with C++26 due to removed deprecated arithmetic conversion on enumerations

[JohelEGP]

Version/Branch of Dear ImGui: Commit 5288687.

Back-end/Renderer/Compiler/OS

Back-ends: N/A.
Compiler: Clang 18, possibly GCC 14.
Operating System: N/A.

Issue:

C++26 will include "Removing deprecated arithmetic conversion on enumerations".
The listed compilers already implement those (https://en.cppreference.com/w/cpp/compiler_support#C.2B.2B26_features):

C++26 feature	Paper(s)	GCC	Clang	MSVC	Apple Clang
Removing deprecated arithmetic conversion on enumerations	P2864R2	14	18

Reproduction:

While building imgui_widgets.cpp:

/home/johel/Documents/C++/Forks/imgui/imgui_widgets.cpp:1682:55: error: invalid bitwise operation between different enumeration types ('ImGuiComboFlags_' and 'ImGuiComboFlagsPrivate_')
 1682 |         IM_ASSERT((flags & (ImGuiComboFlags_NoPreview | ImGuiComboFlags_CustomPreview)) == 0);
      |                             ~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/johel/Documents/C++/Forks/imgui/imgui.h:84:44: note: expanded from macro 'IM_ASSERT'
   84 | #define IM_ASSERT(_EXPR)            assert(_EXPR)                               // You can override the default assert handler by editing imconfig.h
      |                                            ^~~~~
/usr/include/assert.h:100:27: note: expanded from macro 'assert'
  100 |      (static_cast <bool> (expr)                                         \
      |                           ^~~~
/home/johel/Documents/C++/Forks/imgui/imgui_widgets.cpp:3429:67: error: invalid bitwise operation between different enumeration types ('ImGuiInputTextFlags_' and 'ImGuiInputTextFlagsPrivate_')
 3429 |     ImGuiInputTextFlags flags = ImGuiInputTextFlags_AutoSelectAll | ImGuiInputTextFlags_NoMarkEdited;
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/johel/Documents/C++/Forks/imgui/imgui_widgets.cpp:3477:48: error: invalid bitwise operation between different enumeration types ('ImGuiInputTextFlags_' and 'ImGuiInputTextFlagsPrivate_')
 3477 |     flags |= ImGuiInputTextFlags_AutoSelectAll | ImGuiInputTextFlags_NoMarkEdited; // We call MarkItemEdited() ourselves by comparing the actual data rather than the string.
      |              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/johel/Documents/C++/Forks/imgui/imgui_widgets.cpp:6472:50: error: invalid bitwise operation between different enumeration types ('ImGuiTreeNodeFlags_' and 'ImGuiTreeNodeFlagsPrivate_')
 6472 |         flags |= ImGuiTreeNodeFlags_AllowOverlap | ImGuiTreeNodeFlags_ClipLabelForTrailingButton;
      |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4 errors generated.

[JohelEGP]

Here you can see MSVC warn, and GCC provide an opt-out flag: https://cpp1.godbolt.org/z/Wqb5z4zjT.

[cfillion]

See #3040, that warning is from C++20: https://wg21.link/P1120R0.

P2864R2 for C++26 seems to actually be about undeprecating part of that (except the one about constants from different enums).

EDIT: Ah no never mind, I misread it.

Otherwise, if one operand is of enumeration type and the other operand is of a different enumeration type
or a floating-point type, the expression is ill-formed

That paper proposes using +TheConstant to promote it to an integer as a workaround.

[ocornut]

Closed by #7089, thank you.