Meaning of -i and -hidir

[Carter Schonwald]

I would assume the -i is for include c header search paths but I could be
wrong

On Sat, Oct 23, 2021 at 6:00 AM Oleg Grenrus <oleg.grenrus at iki.fi> wrote:

> 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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