[bug#64213] [PATCH] gnu: imgui-1.86: Fix build for mangohud.

[John Kehayias]

Hi guix,

The mangohud package was broken (corrupted display) with commit 
<https://git.savannah.gnu.org/cgit/guix.git/commit/?id=0d5746ee7ca337dcc82553ca6dd794b04bb6563d>
 I'm not sure why that change in build option does it, but trying to run 
"mangohud glxgears" exits immediately with

--8<---------------cut here---------------start------------->8---
❯ guix time-machine --commit=0d5746ee7ca337dcc82553ca6dd794b04bb6563d -- shell 
mesa-utils mangohud -- mangohud glxgears
amdgpu: unknown (family_id, chip_external_rev): (145, 1)
libGL error: failed to create dri screen
libGL error: failed to load driver: radeonsi
amdgpu: unknown (family_id, chip_external_rev): (145, 1)
libGL error: failed to create dri screen
libGL error: failed to load driver: radeonsi
[2023-06-21 Wed 21:01]  [MANGOHUD] [info] [config.cpp:118] skipping config: 
'/gnu/store/25y85hj066crw9kqd4c1jlg6yifd2wiv-mesa-utils-8.4.0/bin/MangoHud.conf'
 [ not found ]
[2023-06-21 Wed 21:01]  [MANGOHUD] [info] [config.cpp:118] skipping config: 
'/home/john/.config/MangoHud/glxgears.conf' [ not found ]
[2023-06-21 Wed 21:01]  [MANGOHUD] [info] [config.cpp:118] skipping config: 
'/home/john/.config/MangoHud/MangoHud.conf' [ not found ]
amdgpu: unknown (family_id, chip_external_rev): (145, 1)
libGL error: failed to create dri screen
libGL error: failed to load driver: radeonsi
amdgpu: unknown (family_id, chip_external_rev): (145, 1)
libGL error: failed to create dri screen
libGL error: failed to load driver: radeonsi
[2023-06-21 Wed 21:01]  [MANGOHUD] [error] [loader_nvml.cpp:42] Failed to open 
64bit libnvidia-ml.so.1: libnvidia-ml.so.1: cannot open shared object file: No 
such file or directory
[2023-06-21 Wed 21:01]  [MANGOHUD] [error] [nvml.cpp:43] Failed to load NVML
[2023-06-21 Wed 21:01]  [MANGOHUD] [info] [overlay.cpp:768] Uploading is 
disabled (permit_upload = 0)
glxgears: imgui.cpp:7475: bool ImGui::DebugCheckVersionAndDataLayout(const 
char*, size_t, size_t, size_t, size_t, size_t, size_t): Assertion `sz_idx == 
sizeof(unsigned int) && "Mismatched struct layout!"' failed.
--8<---------------cut here---------------end--------------->8---

The last line usually indicated a mismatch in imgui versions somewhere, but for 
some reason it comes from this build option. I guess mangohud somewhere assumes 
a different type. (All the previous lines are present when working correctly.)

I've tested this builds and fixes the problem, I just didn't push it directly 
as I wasn't sure if there was a better way to do this change in a package 
inheritance. Anything clever? I would guess not since it is a custom build 
phase with 'invoke', but thought I'd give it a chance for any quick comments in 
case there's something cleaner.

Thanks!
John

0001-gnu-imgui-1.86-Fix-build-for-mangohud.patch
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