Compile failure on MacOS w/ GLFW

[asivitz]

The current version does not build for me on MacOS (m1, GHC 8.10.7). I'm using the GLFW flag, but I suspect I might get other failures even with different flags.

022-08-23 13:59:47.286836: [info] dear-imgui  > [ 2 of 17] Compiling DearImGui.GLFW
2022-08-23 13:59:47.636796: [warn] dear-imgui  >
2022-08-23 13:59:47.637035: [warn] dear-imgui  > /private/var/folders/f6/yyydf8_149gg2pc9pm3wvgcw0000gn/T/stack-5c40579330f2d8c1/dear-imgui-2.1.0/In file included from /var/folders/f
6/yyydf8_149gg2pc9pm3wvgcw0000gn/T/ghc7845_0/ghc_16.cpp:2:0: error:
2022-08-23 13:59:47.637096: [warn] dear-imgui  >
2022-08-23 13:59:47.637128: [warn] dear-imgui  >
2022-08-23 13:59:47.637319: [warn] dear-imgui  > /private/var/folders/f6/yyydf8_149gg2pc9pm3wvgcw0000gn/T/stack-5c40579330f2d8c1/dear-imgui-2.1.0/imgui/imgui.h:252:5: error:
2022-08-23 13:59:47.637363: [warn] dear-imgui  >      error: unknown type name 'constexpr'
2022-08-23 13:59:47.637384: [warn] dear-imgui  >         constexpr ImVec2()                      : x(0.0f), y(0.0f) { }
2022-08-23 13:59:47.637402: [warn] dear-imgui  >         ^
2022-08-23 13:59:47.637417: [warn] dear-imgui  >     |
2022-08-23 13:59:47.637433: [warn] dear-imgui  > 252 |     constexpr ImVec2()                      : x(0.0f), y(0.0f) { }
2022-08-23 13:59:47.637450: [warn] dear-imgui  >     |     ^
2022-08-23 13:59:47.637496: [warn] dear-imgui  >

As far as I understand, DearImGui.GLFW has this inline-c call:

C.include "imgui.h" -- I think it's from this line? Not sure.

and we should be using a c++ compiler with -std=c++11. But we're not (only on MacOS I assume).

The cabal library has

  cxx-options: -std=c++11

but that doesn't seem to be enough.

I am actually able to fix the issue by adding

 ghc-options:
    -optcxx-std=c++11
    -optcxx-Wall

as I did in this commit: https://github.com/haskell-game/dear-imgui.hs/commit/e6c40ff93da1bf748aa08af47f5bcb1b8601cb76

I got this idea from https://github.com/fpco/inline-c/blob/master/inline-c-cpp/inline-c-cpp.cabal#L46

But I'm not sure exactly what the fix should look like for this package.

Would be happy to make this a PR if it seems like a reasonable solution. (Side note: do we support GHC < 8.10?)

[dpwiz]

Please do. The only missing thing is a os flag:

if os(darwin)
  ghc-options:
    -optcxx-std=c++11
    -optcxx-Wall