On Tue, Jun 23, 2026 at 10:48 AM Evan Laforge <qdunkan@gmail.com> wrote:
On Tue, Jun 23, 2026 at 6:44 AM Zubin Duggal <zubin@well-typed.com> wrote:
Which platform/OS are you building on and how did you obtain GHC?
Oh I should have mentioned, it's OSX, 26.5.1. Obtained via ghcup, and using the "ghcup" channel rather than vanilla.
However, I just tested this with linux on a GCP VM and ghc 9.10.3 and I still see the issue. One thing, I see in your non-reproduction that it says "[1 of 3] Compiling BugA ( BugA.hs, BugA.o )", which implies -fobject-code is still on. The bug only seems to happen when you are in bytecode mode, but there are .o files available to load, so you'd have to restart ghci without -fobject-code.
Hate to nag but... has anyone managed to reproduce it? I can make it happen on linux and OSX, and I can verify that it doesn't happen in 9.2.8, and that it starts happening at 9.4. I believe this is when ghc got a new recompilation avoidance mechanism that was supposed to use hashes instead of mtimes, so that's my guess about what introduced it. I guess I can go ahead and file a bug on gitlab now. I'm pretty sure now it's a bug so I guess I don't need to wait for someone else to repro but it would be nice to verify... Since permanently leaving on -fobject-code seems to be a workaround and processors are so fast now, I may just leave that flag on now. I'm surprised more people haven't run into this problem in the years since 9.4.