Exception: expectJust upsweep1, reloading an hs-boot file in GHCi
I unfortunately don't have a reproducer for this bug, and it only occurred once, but I thought I should write it down anyway.
I had a package partially loaded in
GHCi, and changed the module
MyModule, which has an associated
hs-boot file. This forced recompilation of the
hs-boot file, giving the following error:
cabal repl MyPackage Preprocessing executable 'MyExecutable' for MyPackage-0.1.0.0.. GHCi, version 8.8.4: https://www.haskell.org/ghc/ :? for help [1 of 37] Compiling [...] [2 of 37] Compiling [...] [...] [29 of 37] Compiling [...] SomeOtherModule.hs: error: [some correct error message] Failed, 31 modules loaded. -- at this point I edit MyModule.hs and reload > :r [23 of 37] Compiling MyModule[boot] ( MyModule.hs-boot, interpreted ) *** Exception: expectJust upsweep1 CallStack (from HasCallStack): error, called at compiler\\utils\\Maybes.hs:56:27 in ghc:Maybes expectJust, called at compiler\\main\\GhcMake.hs:1528:32 in ghc:GhcMake > :r [ ... compiling modules ] Ok, 37 modules loaded.
As the above log shows, reloading made the error go away and I can't seem to reproduce it. The error message seems to point to
GHC version: 8.8.4
Operating system: Windows 10 x64