Regression: mex command failed to find mingw64 g++ even MW_MINGW64_LOC was defined

[fangq]

this seems to be a recent regression on setup-matlab (although I can't exclude the possibility that something in my script that has caused this, or github's windows-2019 runner).

previously, my github action script can build a mex file on windows without any issue using mingw64 g++ (by defining MW_MINGW64_LOC), see a successful build on Oct 7 (expand the section Build mcxlabcl for MATLAB)

https://github.com/fangq/mcxcl/actions/runs/6443229681/job/17494922687

however, I just made some changes in my C code without touching the github action script, mex failed with the following error:

Supported compiler not detected. You can install the freely available MinGW-w64 C/C++ compiler; visit https://www.mathworks.com/matlabcentral/fileexchange/52848-matlab-support-for-mingw-w64-c-c-compiler. For more options, visit https://www.mathworks.com/support/compilers.

switching matlab from latest to R2022a did not solve this problem

https://github.com/fangq/mcxcl/actions/runs/6684861633/job/18162546536 (using latest)
https://github.com/fangq/mcxcl/actions/runs/6684966422/job/18162772877 (using R2022a)

from the log, you can see MW_MINGW64_LOC was defined the same way as it was before.

I am not sure if this is caused by github runner image changes, or this is related to matlab changes.
Please let me know if have any suggestions.

[fangq]

I further confirm this issue by rerunning one of the previously successful jobs without changing anything, yet, the resubmitted job failed with the same error:

here is the failed job log:
https://github.com/fangq/mmc/actions/runs/6356350750/job/18163174446

here is the previous successful job
https://github.com/fangq/mmc/actions/runs/6356350750/attempts/1

no change was made to the code.

[mcafaro]

I would not expect setup-matlab to be involved here. latest switched to R2023b in mid-September and the original successful build was run long after that (Oct 7th), so I would not expect that switch to be involved either.

Have you tried to confirm chocolatey is still installing mingw64 in the same location?

[mcafaro]

Looking at some of the changes to the windows-2019 GitHub runner README, it looks like Mingw-w64 was removed from the list of preinstalled software recently: actions/runner-images@2ffd260#diff-816219d3c9f30fcc1c40f88ca826c1662bf99eded781c1b419dd2dfb577ae227L75

That seems like a potential culprit. You may need to install it manually now.

[fangq]

thank you so much for noticing this package change in the log! after installing mingw64 on windows, the issue is gone.

much appreciated!