Description
Describe the bug
cabal 3.4.0.0 uses the use_process_jobs flag for all created processes. See: #6529 and #6536
The problem is that hsc2hs.exe also uses the use_process_jobs flag to create its sub-processes (like when it calls gcc.exe)
See: https://github.com/haskell/hsc2hs/blob/24100ea521596922d3edc8370b3d9f7b845ae4cf/Common.hs#L43
This is a problem because on Windows 7:
A process can be associated only with a single job. [...] If a process is associated with a job, all child processes it creates are associated with that job by default.
which is documented by Microsoft here: https://docs.microsoft.com/en-us/windows/win32/api/jobapi2/nf-jobapi2-assignprocesstojobobject (Note that on Windows 8 and above there is no problem)
What ends up happening is that inside hsc2exe.exe, inside createProcess, the call to the Win32 function AssignProcessToJobObject fails:
"C:\ghc-8.10.3\bin\hsc2hs.exe" "@C:\Users\bitc\myproject\dist-newstyle\build\x86_64-windows\ghc-8.10.3\myproject-0.6.2.3\build\My\Module\hsc258F.txt"
hsc2hs.exe: C:\ghc-8.10.3\lib\../mingw/bin\gcc.exe: createProcess: permission denied (Permission denied)
Explanation: hsc2hs.exe is running inside a "job" (that was created by cabal.exe). hsc2hs.exe launches gcc.exe and now gcc.exe is also running inside the same "job". Immediately after launching gcc.exe, hsc2hs.exe creates a new "job" and tries to put gcc.exe into this new job (AssignProcessToJobObject) but this call fails because gcc.exe already is part of a "job" (the one it inherited from hsc2hs.exe).
AssignProcessToJobObject is called here: https://github.com/haskell/process/blob/5a0cbd46eca6d30b78726688058b7fd258a2253d/cbits/runProcess.c#L742
Solution
When cabal calls hsc2hs.exe it should set use_process_jobs = False, so that hsc2hs.exe will be able to use this flag. This is valid because hsc2hs.exe doesn't use exec, it properly awaits on its own children.
When cabal calls ghc.exe, gcc.exe, or other tools, it may set use_process_jobs = True (because they themselves don't set the use_process_jobs flag)
Another Solution
It may be possible to utilize CREATE_BREAKAWAY_FROM_JOB somehow (either in cabal or in hsc2hs). See: https://docs.microsoft.com/en-us/windows/win32/api/jobapi2/nf-jobapi2-assignprocesstojobobject
Alternative Solution
cabal should officially drop support for Windows 7 (a shame)
System information
- Windows 7
- cabal 3.4.0.0
Thank you