This looks like a bug. -hidir documentation says
Redirects all generated interface files into ⟨dir⟩, instead of the default. Please also note that when doing incremental compilation (by ghc --make or ghc -c), this directory is where GHC looks into to find interface files.
And documentation for -i doesn't mention looking for interface files. So by doing % ghc -dynamic-too -c lib/Lib.hs -odir odir -hidir hidir_Lib % ghc -dynamic-too -c Main.hs -odir odir -hidir hidir_Main -ihidir_Lib 1 % ghc odir/Lib.o odir/Main.o -o Demo % ./Demo True everything compiles, TH is run, and demo works. The result files are % find . . ./Demo ./Main.hs ./hidir_Main ./hidir_Main/Main.dyn_hi ./hidir_Main/Main.hi ./odir ./odir/Main.dyn_o ./odir/Main.o ./odir/Lib.dyn_o ./odir/Lib.o ./hidir_Lib ./hidir_Lib/Lib.dyn_hi ./hidir_Lib/Lib.hi ./lib ./lib/Lib.hs --- The confusing error is caused by Lib module in libiserv: https://hackage.haskell.org/package/libiserv which GHC picks! If we rename your Lib module to Library, the error is way better: Could not find module ‘Library’ I also tried using same -hidir when compiling both modules, then GHC still cannot find the Library interface, even the documentation says it should. Please open a GHC issue at https://gitlab.haskell.org/ghc/ghc/-/issues - Oleg On 22.10.2021 19.16, Domínguez, Facundo wrote:
Dear devs,
I'm confused about the meaning of -hidir and -i. Here's my experiment with both ghc-9.2.0 and ghc-8.10.4.
$ find ./Main.hs ./lib/Lib.hs
$ ghc -dynamic-too -c lib/Lib.hs -odir odir -hidir hidir_Lib
$ ghc -dynamic-too -c Main.hs -odir odir -ihidir_Lib -hidir hidir_Main
Main.hs:3:1: error: Bad interface file: hidir_Main/Lib.hi hidir_Main/Lib.hi: openBinaryFile: does not exist (No such file or directory) | 3 | import Lib | ^^^^^^^^^^
If I only use -hidir, it still fails with another error
$ ghc -dynamic-too -c Main.hs -odir odir -hidir hidir_Lib
Main.hs:7:29: error: Variable not in scope: f | 7 | main = print $(runIO (print f) >> [| True |]) | ^
If I use both -i and -hidir pointing to the same folder, then it works!
$ ghc -dynamic-too -c Main.hs -odir odir -ihidir_Lib -hidir hidir_Lib
Now, is this behavior a bug or a feature? And if it is a bug, what is the expected behavior?
Programs copied below.
Thank you! Facundo
$ cat lib/Lib.hs module Lib where
f :: Int f = 1
$ cat Main.hs {-# LANGUAGE TemplateHaskell #-}
import Lib import Language.Haskell.TH http://language.haskell.th/
main :: IO () main = print $(runIO (print f) >> [| True |])
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