Compiling mujoco with MinGW fails because of thread-safe localtime

[maximilian-maisel-bl]

Intro

I'm compiling Mujoco for different targets in a Linux-based CI.

My setup

• Ubuntu 24.04 amd64
• Mujoco 3.4.0

What's happening? What did you expect?

Building Mujoco with MinGW fails because it doesn't recognize thread safe localtime implementation.

[  6%] Building C object CMakeFiles/mujoco.dir/src/engine/engine_util_errmem.c.obj
/home/user/mujoco/src/engine/engine_util_errmem.c: In function ‘mju_writeLog’:
/home/user/mujoco/src/engine/engine_util_errmem.c:107:6: error: #error "Thread-safe version of `localtime` is not present in the standard C library"
  107 |     #error "Thread-safe version of `localtime` is not present in the standard C library"
      |      ^~~~~
make[2]: *** [CMakeFiles/mujoco.dir/build.make:532: CMakeFiles/mujoco.dir/src/engine/engine_util_errmem.c.obj] Fehler 1
make[1]: *** [CMakeFiles/Makefile2:1457: CMakeFiles/mujoco.dir/all] Fehler 2
make: *** [Makefile:146: all] Fehler 2

I'd expect that it compiles without errors.

As a workaround, add a || 1 to line 110 #elif _MSC_VER or comment out the block that gets localtime and logs it.

Steps for reproduction

• Building Mujoco with mingw:
  cmake -DCMAKE_TOOLCHAIN_FILE=~/cmake-toolchain-mingw64-x86_64.cmake -DCMAKE_COMPILE_WARNING_AS_ERROR=false ..
• Patch problematic section from mujoco.rc file (Issue Build fails with gcc and mingw makefiles : Syntax Error #839)
• Run make

This is the content of the toolchain file:

set(CMAKE_SYSTEM_NAME Windows)
set(CMAKE_SYSTEM_PROCESSOR x86_64)

find_program(CMAKE_C_LINKER NAMES x86_64-w64-mingw32-ld)
find_program(CMAKE_C_COMPILER NAMES x86_64-w64-mingw32-gcc)
find_program(CMAKE_CXX_COMPILER NAMES x86_64-w64-mingw32-g++)

Minimal model for reproduction

This bug is independent of the model and code.

Code required for reproduction

This bug is independent of the model and code.

Confirmations

• I searched the latest documentation thoroughly before posting.
• I searched previous Issues and Discussions, I am certain this has not been raised before.